·Publication Number 397
AMERICAN LECTURE SERIES
A Monograph in
AMERICAN LECTURES IN LIVING CHEMISTRY
Edited by
1 NENI TO KUGELVASS MD Th D SCD
Consultant to the Departments of Health and Hospitals
Neu York City New York

·CHEMISTRY OF
HEART FAILURE
By
and
WILLIAM C HOLLAND, MD
Professor of Pharmacolog)
Un ersity of Mississippi School of Vedicine
Jackson 1fississippi
Forme ly Professor of Pharmacology
I ande bilt Inuersity School of Medicine
N shielle Tennessee
RICHARD L KLEIN, Ph D
Assists Professor of Pha macology
Unitersity of Mississippi
School of Medicine
Jackson Mf15525St PPI
I 774
CHARLES C THOMAS
Springfield Illinois
PUBLISHER
USA

·CELARIES CHOVAS IUBLISHER
BAWERSTOLE HOUSE
301 327 East Lasrence Avenue Springfield Illinois US!
I ublished simultaneously on the British Commanx ealth of Nations by
BLACKWELL SCIENTIFIC PUBLICATIONS LTD OXFORD ENGLAND
Published simultaneously in Canada by
THE REASOV PRESS TORONTO
This book is protected bs copyright No
part of it may be reproduced in any manner
truthout written permission from the publisher
O 1760 by CHRLES C THOVAS
PUBLISHER
Library of Congress Catalog Cart umbes 60 1891
Wach TUOVAS BOOKS carefast attention is given to alt details of
manufacturing and design It is the Publisher s desire to present booka
that are satisfactory ay 10 their physical qualities and artistic possibilities
and appropriate for their particular use TUOVAS BOOKS will be true
to those laws of quality that assure a good name and good will
Printed in the United States of America

·Dedicated to
Rosa Spence Abbey
and
Natalie Titus Bertonis

·No text on this page.

·PREFACE In this monograph we have attempted to gather in a few pages some of the extensive information pertinent to the mechanism of contraction in the normal and failing heart and the mode of action of digitalis The book has been written so that the medical student clinician and cardiologist with an elementary knowledge of physics and chemistry can learn of the many advances in this field in a few seisure hours Sufficient references on the subject are included so that the ambitious student may delve further if he chooses We feel the book will also appeal to the chemist and physicist who are curious about the development and application of their own subject in another very important field Every attempt has been made to give proper credit to first discoveries Important contributions which have been omitted represent gaps in the authors capacity to find or summarize all of the relevant material WC HOLLAND RI KLEIN

·No text on this page.

·ACKNOWLEDGMENTS
We would like to thank Dr A H Briggs for reading and
criticizing the manuscript Miss Patricia Little for her patience in
preparing the manuscript and Mr J Nelson for his reproduction
of figures
WCH
RLT

·No text on this page.

·CONTENTS Page ובץ Preface Acknou ledgments IX Chapter 1 INTRODUCTION References 8 Chapler II ELEMENTS OF THERMODYMAVICS Introduction Concept of Free Energy Equilibrium and Mass Action Coupling Mechanisms Concept of Energy Rich Bonds Relationship Between Free Energy and Oxidation Work of the Heart The Efficiency of the Heart References 10 10 11 12 13 15 15 16 17 18 Chapter III CHEMISTRY OF THE NORMAL HEART PART 1 FREE ENERGY RELEASE 20 Introduction 20 Reactions of Glycolysis 21 (1) Triose Phosphate Dehydrogenase Phosphorylglyceryl Kinase Reactions 21 (2) Phosphorylglyceryl Mutase Enolase Reactions 24 (3) Furuvate kinase 24 Krebs Citric Acid Cycle and the Electron Transport System 25 Energetic Considerations 28 Alternative Sources of Energy 29 (1) Fatty Acid Metabolism 29 XI ·XIZ Chemistry of Heart Failure (2) Amino Acid Metabolism Summary Localization of Enzymes in the Cell (!) Nucleus (2) Mitochrondria (5) Microsomes (4) Soluble Enzymes (5) Cell Membrane References 32 33 31 31 37 37 37 43 52 Chapter IV CHEMISTRY OF THE ORVAL HEART PART I FREE ENERGY UTILIZKTION Introduction Vlorphological Considerations Chemical Considerations (1) tosin (2) 4c1) (3) Tropomyosin (1) Delta Protein Interaction of Actomyosin and TP Relaxing Factor Localization of Contractile Proteins in Vuscle Theories and Models of Muscle Contraction References 53 59 55 55 56 60 69 Chapter 1 CHE\MISTRY OF THE WORVAL HEART PART III ELECTROLYTE METABOLISY Ion Transport Electrolytes and Cardiac Contraction Bioclectric Parentals Excitation Contraction Coupling The Vature of the Stimulus (!) klcctrochemical (radients ind Diffusion (2) Z Linc and Cool Actation Linkage (3) Sarcoplasmic Reticulum as an Dictation Conduction Votsor GO 66 69 G3 70 21 ·Chemistry of Heart Failure XI11 References 71 Chapter 11 CHEMISTRY OF THE FAILING HEART Disturbances in Free Energy Release (1) Anoxia (2) Coenzyme Lack and Hormonal Imbalance Disturbances in Free Energy Utilization Electrolyte Metabolism Hypertrophy Morphological Considerations Hypertrophy Chemical Considerations References 75 75 76 76 77 78 79 80 81 Chapter 111 85 86 87 ACTIONS OF DIGITALIS Overall Metabolism Free Energy Release Free Energy Utilization Electrolyte Metabolism References 88 89 91 97 Chapter VIII THE NATURE OF CONCESTIVE HEART FAILURE AND THE MODE OF ACTION OF DIGITALIS Theories of Congestive Failure The Mode of Action of Digitalis References 97 101 103 Chapter IX FIBRILLATION Theories of Fibrillation Ionic Mechanisms in Fibrillation Metabolic Events and Fibrillation References 101 105 106 108 108 Chapter Y PERSPECTIVES 111 Index 119

·No text on this page.

·CHEMISTRY OF HEART FAILURE

·No text on this page.

·Chapter 1 INTRODUCTION In order for the heart to perform its necessary function of propelling blood through the circulatory system it must contain the necessary metabolic machinery for the release conservation and subsequent transformauion of chemical potential energy of foodstuffs into mechanical worh During the past fifty years many advances have been made in our understanding not only of the chemical mechanisms involved but also of the physico-chemical events that underlie the conversion of chemical potential energy to mechanical work in both cardiac and skeletal muscle In fact we non have good eudence that one of the principal and final causes of the important forms of congestive heart failure is in essence a failure of the utilization of chemical potential energy These advances have been made possible by application of techniques of classical organic chemistry and physics and also by the development of muscle models such as the glycerinated psoas preparation of Szent Gyorgy11 The latter are of great importance because they stand half way between whole muscle which was the object of classical physiology and the protein and enzyme systems which were studied in the chemical laboratory In the present chapter we would like to revien briefly these major advances In this way the reader may approach the remaining chapters with an integrated ves of events associated with the contraction of the normal and failing heart The history of the chemistry of muscle contraction has been characterized by a relatisely slow evolution of concepts interspersed with periods of resolution in which existing theories were hastily abandoned and nen asenues of thought explored It was early evident that the contractile activity of heart and seletal muscle 1 ·Chemistry of Heart Failure depended upon oxygen consumption and metabolism of foodstuffs such as carbohydrates By the late twenties it was realized that the relation of these metabolic processes to the contractile process was an indirect ont Unul this time it was believed that lactic acid was the agent that drove the contractile machinery Lundsgtare s dis covery 3 that contraction persisted after all respiration and lactic acid formation was eliminated dispelled this idea quickly Hegave eudence that the chemical crent supporting contraction was the brealdoun of phosphocreatine lactic arıd production occurred after contraction was over HN = CNN POH OH N - CH, CH COOH Phosphocreatine I few ycars Inter Iohmannt proposed that plosplicurcacine 178 onlv indirectly unsolied and the essential role was assigned in adenosine triphosphate (ATP) ITP was broken down to adeno sine diphosphate (IDP) which in turn accepted phosplinte from phosphocrenuine In thuis muner 4 TP was thought to energize the contractilt mechanisin N = = NR CH CN 0 0 0 CH HH H NCMN CCCCCDP-ONPON POR K } RH 1 OH OH ON OH OH Adenosine triphosphate 1s (dence contimed to accumulnte it was soon realized that the prime full dron of glycolysis and respiration was to furnish TV by synthesis froin ADP and phosplizie the processes of respiratie ·Chemistry of Heart Failure 5 were relegated to the recovery phases of muscle activity Mechanı cal work was achieved at the expense of chemical bond energy of ATP with phosphocreatine acting as an additional reserve or source of phosphate bond energy Respiration and glycolysis then resynthesized ATP to replace that which was used up By 1939 a reasonably consistent picture of the energetics of muscle contraction had emerged The problems of the nature of the mechano chemical coupling whereby energy obtained from the breakdown of ATP drove the contractile machinery was left unansiered In 1859 huhne discovered that large quantities of a viscous protein could be extracted from muscle by strong salt solutions He named this protein myosin However it took more than 75 years for the full significance of this fundamental observation to be appreciated because of the inadequate techniques of the time Later optical studies of flowing solutions of myosin revealed a bırefringence which suggested it consisted of elongated molecules This made myosin a likely candidate for the structural component as well as the working substance of the myofibrıl With knowledge of the chemical nature of the working substance and of the energy source ATP the question arose as to whether a definite relation existed between the two entities It was indeed significant when Engelhardt and Ljubimowa in 1939 discovered that myosin was an enzyme adenosine triphosphatase which catalyzed the break down of ATP to ADP From these studies the concept arose that myosit was a contractile enzyme deriving its energy from the hydrolysis of ATP At about the same time Needham and coworkers' shoned that myosin underwent certain remarkable reactions with ATP The birefringence of myosin solutions disappeared or decreased on the addition of ATP Myosin threads prepared by squirting myosin into aqueous solutions contracted with ATP It was apparent that ATP affected the physico chemical properties of myosin und at the same time 175 enzymatically hydrolyzed to ADP These observations were reinterpreted in a difterent light when Szent yorgyı and collaborators showed that myosin was in ·6 Chemisin of Heart Farlure reality a complex of two proteins accin and myosin which they called actomyosin From their findings the idea arose that dur ing the resting state actin ind myosin were hept dissociated and that upon stimulation actin combined with myosin to form acto myosin Upon the adsorption of ATP actomyosin went into a con tracted state The molecular event #175 visualized as a folding or coiling of a polyelectrolyte strand containing actomyosin 10 It is important to note that in this proposed mechanism contraction was energized by the adsorption and not the hydrolysis of ATP Ques tions concerning the localization of these proteins in the muscle fiber and the relation of the chemical events during contraction to the known changes in muscle morphology were still not answered Since the late nineteenth century was known that muscle striations were in important clue to the mechanism of contraction In fact the changes in striations accompanying contraction were accurately and clearly described by the nineteenth century micro scopists 11 but unfortunately no coherent theory of muscle con traction emerged Thesc significant observations were neglected probably because of the rapid progress being made in muscle chemistry and energetics of contraction By 19 20 muscle chemistry had reached a stage in development where it was ready for correlation with structure Furthermore the mechanics and lieat production of muscle liad riso developed sufficiently to be linked with other lines of information on the contractile process By 1915 there was goodi evidence that the process wluch turned on contraction was a reduction of the resting membrane potential and that calcium in some is yet unknown minner played a crucial role in this process of excitation contre tion coupling By 1953 the techniques of thin sectioning for electron micro scopy as well as those for the specific extraction of actin ind myosin from intact muscle fibers were developed to a high (legree Using these methods the Huxleys and their collaborators! 13 were able to teach the problem of localization of the structural proteins in the muscle fiber They found evdence that the misotropic or A band was due to the presence of thich filaments containing myosin They were also able to show that a second set of filaments thinner ·Chemistry of Heart Carlure 7 than the first and containing actin extended from the Z membrane through the isotropic or I band into the A band There the thin actin filaments interdigitated with the thick A band filaments From these studies and a number of others they proposed a rather simple and radically different model of muscle contraction They postulated that the wave of depolarization induced changes which permitted the thin I filaments to slide past the stationary and thicher A filaments and shortening ensued This process was pic tured as being energized by the breakdown of ATP 1s a consequence of the many advances in our knowledge of the chemistry of the normal contractile process it was only natural that the new techniques and ideas were applied early to a study of the nature of the defects in congestive heart failure Much of what was known about the nature of heart failure was obtained from hemodynamic and mechanical considerations and was embodied in the Frank Starling Law of the heart This principle states that the energy of contraction of the heart is a function of the initial length of the myocardial fibers that is the diastolic volume of the heart Scarling showed that contraction energy increased up to a certain optimal length but with further lengthening of the fibers the energy of contraction diminished He felt that this resulted from the fiber being stretched beyond a critical length According to the views of Starling congestive fail ure could be thought of as resulting from excessive stretch of the muscle fibers It has become increasingly apparent that only in the case of failures resulting from anoxia vitamin deficiencies and hormonal imbılınces can a metabolic defect be demonstrated Here a failure of energy release is reasonably clear cut On the other hand in failures resulting from chronic hypertensive and valvular disease in humans as well as in spontaneous failures of the heart lung prepa ration the metabolic patterns appear to be perfectly normal The evidence available to date strongly suggests that the basic defect in these conditions is a failure to transform available metabolic energy into mechanical vork 1* It is only the latter type of failures that respond effectively and efficiently to the digitalis glycosides Several questions arise if we accept the concept proposed by ·8 Chemisiny of Heart Failure Frank and Starling that in final analysis congestive failure results from excessive stretch of the myocardial fibers Does excessile stretch lead to the development of abnormal contractile proteins a failure of excitation-contraction coupling the loss of essenti?? metabolites or electrolytes such as K and Ca or the partial or complete withdrau ai of the tiun actin filaments from the A band where they are normally interspersed among the thicker myosin filaments. The insers to these questions are not 11111?ble it the present time There is evidence that Czlons are somehon inialied in the genesis of congestive fulure It has long heen known that digitalis can in part subscrcute for Ca ions and that Ci sons are required for the beneficial effects of this drug Furthermore it has recently been shown that the digitalis glycosidesss increase the wailable myocardul Ca ions esther at sites in the membrane or in the myo plasm irrespective of any effect they might have on metabolic reactions Many of the problems presented above wll be discussed in some detail in the following chapters REFERENCES 1 Szcnt yorgve Irce energy relations and contraction of acto myosin Biol Bull 26 140 1919 2 Meyerhof o Die Energie umuandlungen im Muskel v Mich suurebildung und mechanische Arbeit Arch ges Physio 191 128 1921 3 Lundsgaard E Untersuchen uber Muskel kontraktionen oline Milchsaurebildung Biochem Zischr 217 162 1929 Lohınannh Uber die enzymatische Sufspuitung der Kretin phosphors inre zugleich ein Pestrz, zum Chemismus der Muskel kontraktion Rtochem Ztschir 271 261 1931 5 huhne Untersuchunger uber Bewegungen und Verandcrun gender contrahtilen Substanzen Arch rinat Pleystol tess med Terp is 564 1859 6 son Varalt A Land Cdsalt ) ? Studies in the physical clients try of muscle globulins II The anisotropy of myosin and the angle of socline J Biol Chem 89 315 1930

·Chemistry of Heart failure
9
7 Engelhardt A and Ljubimowa M N Myosine and adeno
sine triphosphatase Nature 114 668 1939
8 Needham J Shen SC Needham D M and Lawrence ASC
Myosın birefringence and adenylpyrophosphate Nature 147
766 1941
9 Szent Gyorgy: A ed Studies Inst Med Chem Szeged vols 111
1911 3
10 Riseman J and hırkwood JG Remarks on the physico chemi
cal mechanism of muscular contraction and relaxation J Am
Chem Soc 70 2820 1918
11 Foster M 1 Tert Book of Physiology 5th edit London Mac
Inillan 1888
12 Huxley A F and Viedergerke R Structural chinges in muscle
during contraction Vature 173 971 1954
13 Huxley H and Hanson ) Changes in the cross striations of
muscle during contraction and stretch and their structural
interpretation Vature 173 973 1954
14 Bing RJ The metabolism of the heart The Harvey Lectures
1954 5 New York Academic Press 1956
15 Holland WC and Sekul A A Effect of ouabain on Cat and
C130 exchange in isolated rabbit atria Am J Physiol 197 757
1959

·Chapter 17 ELEMENTS OF THERMODYNAMICS Introduction It is very difficult to grasp the full significance of the chemical inechanisms involved in the release and transfor mation of chemical potential energy of foodstuffs into work by the heart without haing an appreciation for the concept of enersy Hiscorically force is the basic concept in the consideration of energy Force is measured in tcrins of acceleration imparted in unit mass Work is defined as the action of force over unit length and energy as the ability or cap?ory to do nork Energy appears in various forms heat light Kinetic mechanical work electrual potential and chemical The First law of thermoclynainis states that energy can change its form but not its quantity In thermochemistry the chemical potential energy of a given substance is evpressed quinti rauncy is its lieu equialent (IN ET45 joules or calories) The Second Lant of thermodynimes places restrictions on the exchange and transformation of this hent ecur aleut Stated simply heal runot be transformed into work unlcss temperature difficiles exist in the systein as is the case with a heat enginc in isothermal systems such as the living cell where no temperature sliferentes exist exchange and transformation of energy can occur without wasteful loss is best only by a process of coupling berheen the reaching components Furthermore the exchange can only occur Thith high efficiency berst een substances of comparable chemu 1) potential Obviously the biological system is not lihe 2 hent engine and cannot convert heat and pressure Ganges into work for instance the utilization of enerb) from the chemical reaction C,H, 0. + 60 GCO + GH O + Energy ·Chemistry of Heart Failure 11 must be achieved by reactions designed to trap the energy released These reactions must be of such a nature that large quantities of chemical potential energy are broken up into smaller biologically useful pachets of the order of 10 to 12 kcal to accommodate the dimensions of the energy currency of the cell The chemical reactions involved in this constant flow of energy in biological systems are catalyzed by enzymes or biocatalysts A study of energetics provides an intimate knowledge of metabolic pathways and life processes Furthermore the principles of ener getics are of value in predicting whether or not a particular reaction is thermodynamically possible and the extent to which 1 reaction may proceed Enzymes only hasten the attainment of equilibrium and cannot catalyze energetically unfu orable reactions nor change the final equilibrium ratio of reactants to products Concept of Free Energy In chemistry it is well known that all chemical compounds contun potential energy This energy is in the form of forces that hold atoms together When chemical substances react part of that energy may be converted into work in other chemical systems It is therefore extremely important to know the amount of work that cin be obtained froin the reac tions of a given compound It is known from thermodynamical considerations that at a given temperature only a portion of the total energy of a system may be used for work This fraction avul able for work is known as the free energy It can be defined as the maximum amount of work that can be obtained from a system The symbol F is used to denote this quantity In actual practice not all of the maximum available energy of any particular system is used for work some of it is wasted as friction ind heat The efficiency of the system a measure of the fraction of the maximum available energy that is converted to work Most biological systems have efficiencies of the order of 30 to 60 percent Thus if it were possible to carry out a reaction under ideal conditions the work that reaction could do is the free energy For any specific system we cannot specify the absolute value of free energy Horvever if the system undergoes a change there will be a change in free energy AF which can be measured That fraction of the total energy of a system that is unarul ·12 Chemistry of Heart Iailure able for work is called entropy and has been guten the syinbol $ Agın only changes in S AS can be measured There is a relatnely simple relation betneen the total energy the free energy and entropy of any given system HSF + TS or when the system undergoes change AH=AF + TAS AHK a change in internal energy or for practical purposes the toral energy and T is the absolute temperature at which the trans formation occurred from these considerations it can be seen that of the total energy change accompmyung a chemical trinsformation at a given temperature Al is that tvailable for work and AS 15 that unavailable it is evident from the equation that the sign and size of AF will reflect contributions from both the changes in in ternal energy and the changes in entrops during the transformation Changes in free energy AF other than providing 2 incasure of the maumum amount of energy which may be obtained as work in the course of a material change also provides a quinnitatile indication of the potential ability of the chemical substance to undergu transformation Depending upon the sign (=) of free energy chinge reactions may be classified as exergonic or euder gonic Exergonko rezcions kase a - AF and tend to proceed spon taneously such as hydrolytic reactions On the other hand in endergonic reaction with a +AF must be coupled with an exer gonic reaction in order to proceed spontaneously Vany biosyn thetic reactions fall into tius group Due to the difficulties in estimating changes in entropy AS changes in frce energy can be determined by other methods such as froin equlibrium dat? by the following reloon AF-2303RT log K uliere R is the fis constant (1 98 calories per degree per mole) T the absoluc cemperature and h the equlbrium constant for the reaction Equilibrium and Hae trtion The above expression leads ils immediately to a cliscussion of the Law of Vass Action in a general ·Chemistry of Heart Failure 13 way the law of mass action is an expression of the fact that (1) the rates of chemical reactions are proportional to the active masses of the substances reacting and (2) in a reversible reaction the ultimate position of equilibrium is determined by the ratio of the active masses of the reaction products and reacting substances In 1 reaction such as A+B=C+D at equilibrium the following relation holds (C) (D) AF=AF +2 303RT log (A) [B] where the concentrations are those at equilibrium The ratio of the concentrations of products to reactants is known as the equi librium constant The term AF 15 1 constant for the reaction and is called the standard free energy change when the reactints and products are all present in their standard states oi unit con centrations (1 atmosphere pressure for gases pure liquids or solids and one molal for solutes) AF- AF° The necessity for having such a constant for any reaction is apparent since we cannot record AFs for all possible concentrations of reactants and products In a reaction which has reached equilibrium the reactants and products are exchanging molecules at the same rate Therefore AF - O and the equation becomes AF = -2 303RT log K It should be apparent from this relation that the sign of AF is a measure of the spontaneity of chemical change for example if k is greater than I (more products than reactants) the log of his positive and Afº is negative On the other hand if k is less than I the log of k is negative and AF will be positive When K= 1 the log of K=O AF° = 0 and the reaction is freely reversible with no net accumulation of reactants or products Coupling Mechanisms At first glance it might appear that a reaction with a +AF° cannot occur at all Many such reactions however are known to occur in nature The reason they occur lies in the fact that living systems provide a coupling mechanism whereby energy of an exergonic reaction (that is one with a -AF) ·12 Chemistry of Heart I ailure able for work is called entropy and has been gien the symbol S Again only changes in S AS can be mersured There is ? relatively simple relation between the total energy the free energy and entropy of any guen system HF + TS or when the system undergoes change AHEAF+TAS AH is a change in internal energy or for practscal purposes the total energy and T is the absolnte temperature at which the crans formation occurred from these considerations it can be seen that of the total energy change acompanying a chemical transformation at a given temperature AF is that available for work and AS 15 that unavailable it is evident from the equation that the sign and size of AF will reflect contributions from both the changes it in ternal energy and the chinges in entropy during the transformation Changes in free energy AF other than providing a measure of the maximum amount of energy wluch may be obtained as work in the course of a material change also provides a quitaine indication of the potential ability of the chemical substance 10 undergo transformation Depending upon the sign (*) of free energy change reactions may be classified as exergonic or ender gonic Exergonic reactions have a - AF and tend to proceed spon treously uch as hydrolytic reactions On the other hand an <ndergonic reaction with a + at must be coupled with an exer gonic reaction in order to proceedi spontaneously Vany brosyn thetic relations fail into this толір Due to the difficulnes in estimating changes in entropy as changes in free energy can be determined by other methods such as from equilibrium data by the following relation AF=-2 303RT logh Where R is the gas constant (1 98 calories per degree per mole) T the absolute temperature and I the equilibrium constant for the Tenction Fqutlılırium and Maes (chon The above expression leads us immediately to z discussion of the Law of Vase Action In general ·Chemistry of Heart failure 15 nine phosphate in intertebrates The mechanism of exchange is known as the Lohmann' reaction creatine + ATP = ADP + phosphocreatine This reaction has a sery small A F° which means that the energy of ATP exchanges smoothly and with high efficiency Concept of 'Energy Rich' Bonds It will be noted that ATP contains pyropliosphate bonds Such chemical bonds liberate rela tively large amounts of free energy upon hydrolysis Lipman referred to these bonds as high energy bonds and designated them with the symbol 1 in contradıstinction to those bonds which release relatively small amounts of free energy upon hydroly sis such as simple phosphate esters The symbol is not also used for other high energy bonds not involving phosphate In Table I a number of such subst inces are listed with their standard free energies of hydrolysis Relationshup Between Free Energy and Oxidation It is now known that 60 to 80 per cent of the total free energy available in ſoodstuffs is released during the oxidative phase of metabolismı 3 Oxidation may be defined as the loss of electrons and reduction as the gain of electrons A typical oxidation reduction system may be written as reduced form = oxidized form + ne where n is the number of electrons (e) involved in the reaction The maximum available work thit can be obtained from such a reaction in which a transfer of electrons occurs may be described in terms of the potential difference or electromotie force All oxidation reduction reactions of which there are many in nature may be so described Tlie equation relating A F to the electro motive force is AF=--OFE where n is the number of electrons taking part in the reaction F is the faraday (23 068 calories per solt equivalent) and C is the potential or experimentilly measured quantity E is related to ·16 Chemistry of Heart Failure TABLE 1 STANDARD FREE FNERTIFS OF 115 DROLSSS OF SOME 1 TORTAVE POSTITATE COVOLANDS Compound Rond Type AF Colt 9200 --3000 3000 - 12000 a Glycerophosphate Clucose 6 phosphate Fructose 6 phosphate Adenosine triphosphate Inorganic pyropfrosphate Creatine phosphate Phosphorylenolpyrusate Acetylphosphate Acetyl cocnzyme A ester phosphace estes phosphate ester phosphate pyrophosphate pyrophosphare nitrogen prosphate cnal phosphate acyl phosphate hof phosphale --000 11.800 -1 15 000) - IX concentration of the oxidized and reduced forms by the following relation RT (oxid) EE° +2 303 log nF (red) where E is the standard electrode potential and equal to 1 when the system is half reducec! Work of the leart The mechanical stork performed by the heure during each contraction has customarily been calculated from the sum of the pressure energy and Linerre energy imparted to the volume of bloos ejected The differences bet een pressures in aorta and pulmonary artery makes necessary to perform calcu lations for the left and right ventricles indsidually The user of atr11 is usually neglected The work for each sentricle is expressed ly W OP+ POV 2G «here is the volume of blood ejected P the mean ſerial pres sure Vthe velocity of ejection indo the density of blood is the grafitsonal constant ·Chemistry of Heart I arlure 17 For the left ventricle q = 60 crn? P = 100 mm Hg = 136 cm Water V = 50 cm/sec and p = 106 in the human at rest then 106 X 60 X 50 W = 60 X 136 + 2 X 980 8 160 + 80 = 8 240 g cm For the night sentricle q = 60 cm, P = 20 min Ho = 27 cm water V = 50 cm/sec then = 1 620 + 80 = 1700 g-cm = The total work under resting conditions = W + W 9 910 g-cm or approximately 100 g m per beat For 1 heart rate of 70/min this amou als to 7000 g m/min or 420 hg m/hr In hard exercise the total work per hour may reach 4 000 kg m/hr In heat equivalents thuis amounts to 983 9 cal/hr during rest and 9 370 8 cal/lır during hard exercise The Efficiency of the leart The overall efficiency of the heart can be pictured is comprising the purely mechanical effi ciency as a pump and the efficiency of conversion of chemical energy derived from the fuel supplied into external mechanical work done on the blood circulation The efficiency of conversion of chemical energy into mechanı cal work by the muscle fibers can only conveniently be estimated by comparing the cheniical energy released and the external work developed over a given period it is (isually calculated indirectly by comparin, the work performed with the myocardial usage of o In the past calculations were made neglecting the contribution of anaerobic metabolism to energy production and consumption of the resting non beating heart There is no evidence to indicate that anterobic metabolism contributes much to energy production On the other hand recent studies have shown that the consump tion of the non bcauing heart is 20 to 35 per cent of that of the beat ing heart. In the case of the dog heart Bing has shown that the O usage of the beating heart is 25 11 ml/min and 4 83 ml/min for the arrested heart The O, utilization of the latter is 20 percent of that of the former Therefore 20 per cent of the total O usage ·18 Chemistry of Heart I ailure of the left ventricle is used for basal metabolic processes exclusive of work The efficiency during contraction is work of heart X 100 usage/mın x 2 059 X 08 where 2 059 is the energy equn alent of 1 ml of O at an RQ of 082 and 0 8 is the fraction used in contractile work Viking the suggested corrections Bing calculates myocardial efficiency to be 37 per cent in the dog and 39 per cent in man He further esti mates that 87 per cent of the energy stored in ATP is converted into mechanıcıl work by the heart REFERENCES Lohman konstitution der Idens lpyrophosphors wure und Adenosindiphosphorsaure Biochem Ztschr 282 120 193) 2 Lipman F Vietabolic generation and utilization of phosphate bond energy ddtances In mol 1 99 1911 3 Ramirez ) Oxidation reduction changes of cytochromes follow mg stimulation of amphibian cardiac muscle J Physiol 117 11 1959 Bing R J and Michal G Myocardial efficiency Ann Vew lork Acad Sc 72 555 1959 General Readings Clarl + V Topics in Physical Chemistry I altimore Williams and Wilkins 1918 Daniels F and Alberty RI Physical Chemistry less Jork Tliley 1959 Dixon and Webb LC Inimes New York Icademic Press 1998 Edsall J T and Ilyman J Brophysical Chemistry lol I leu Sork Academic Press 1958 Classtones Thermodynamics for Chemists Nes jock Von los trand 1917 Guggenheim E A Thermodynamics 2nd edit New York Inter science 1930

·Chemistry of Heart Failure
19
Klotz I \ Energetics in Biochemical Reactions Seu Jork Academic
Press 1957
Neilands J B and Stumpf I Outlines of En.)me Chemistry
\cu Tork Illey 1937
Rutgers J Physical Chemistry Ves Tork Interscience 1991

·Chapter III CHEMISTRY or THE NORMAL IICART PART I FRCE ENCRGY RELEASE Introduction The heart is a compret muscle muss with the fundamental function of converting chemical potential energy into mechanical work As in skeletal muscle lieart derives its energy from the breakdown of certain essential foodstuffs by a complex series of enzyme catalyzed reactions The purpose of these reactions is to release free energy in such form that it can be stored in energy rich compounds ATP is the prototype The free energy is even tually utilized by the contractile apparatus to perform mechanical vorh There is every reason to beliese that the fundumental process connected with energy production is the oxidation of foodstuffs the essential substrates are carbohydrate in the form of glucose und fatty acid Oxidation of foodstuffs is a step wise process which being diverse for the various substances inually is quite uniform as the substrates reach the final stages of free energy release The reactions proceed simult ineously under the influence of enzynies The activity of these enzymes in turn is dependent upon smaller organic substances called coenzymes Coenzymes are in large part derivatives of the well known vitamins of the B complex and con stitute a means by which the nutritional stite may influence metabolism Hormones are another important class of chemical regulators They appear to exert their effects on metabolism by controlling the transport of essential metabolites across biological membranes For example it has been shown that insulin enhances the entry of glucose into the cell independent of any effect on metabolic Terctions 1 20 ·Chemistry of Heart Failure 21 In the present chapter we shall briefly outline what is known of the intermediate steps involved in free energy release in the normal heart Much of what is to be said concerns free energy metabolism as we know it in skeletal muscle Recent studies strongly indicate that both heart and sheletal muscle derive their energy for con traction in the same manner and from the same foodstuffs Information has been obtained necessarily from studies on tissue slices homogenates and isolated enzymes However investigations on the intact heart both in vivo ind in vitro lene no doubt that metabolic patterns to be disc ussed are of physiological significance 3 As pointed out earlier the prime function of metabolism is the release and subsequent trapping of free energy in the form of energy rich compounds for eventual utilization by the contractıle apparatus in the performance of work There is strong evidence that one of the primary sources of free energy is carbohydrate in the form of glucose The ultimate breakdown of glucose can be classified into several types of transformations glycolysis krebs citric acid cycle and the electron transport system Reactions of Glycolysis Glycolysis can be defined as the sum total of enzyme catalyzed reactions in which glucose is degraded to two molecules of lactic acid In order for glucose to enter this pathway it must be phosphorylated to glucose 6 phosphate by ade nosinetriphosphate and the enzyme hexokinase Once formed glu cose 6 phosphate may be incorporated into glycogen by way of glucose 1 phosphate or it can enter the main glycolytic series of reactions ultimately to be broken down into two molecules of pyruvate or lactate Under anaerobic conditions pyruvate is con verted to lactate In Figure I we have outlined some of the major reactions involved Lven though this is not the proper place to discuss every step of glycolysis in great detail certain of the steps are very important to our understanding of free energy release These reactions illus trate in a most elementary way how chemical potential energy is released and conserved in the form of high energy compounds (1) Triose Phosphate Dehydrogenase Phosphorylglyceryl kinase Reaction The oxidation of 3 phosphoryl D glyceraldehyde formed by the cleavage of fructose 1 6 diphosphate is an extremely ·22 Chemistry of Heart Failure Glycogen 11 Glucose l-phosphate Glucose 1 6 diphosphate 11 Glucose 6 phosphate Glucose - ATP ADP Fructose +Fructose 6 phosphate ATP ADP ATP ADP Fructose 1 6 diphosphate 11 3 Phosphoryl D glyceraldehyde Glycerol Dihydroxyacetones phosphate 13 Diphosphoryl D glycerate ADP K ATP 3 Phosphoryl D glycerate 11 (2 3 Diphosphoryl D glycerate) 12 2 Phosphoryl D glycerate 11 Phosphorylenolpyruvate ADP ATP Lactic Pyruvate+KREB S CITRIC ACID CYCLE Acid Figure 1 Quiline of the glycolysis reaction ·23 Chemistry of Heart Failure important reaction It Illustrates in a clear manner those chemical events associated with rearrangement of bond energy of the original substrate glucose whereby it is transferred and conserved in energy rich compounds The nature of this reaction was estab lished in Warburg s laboratory CH 0 –H PO 1 CH,0 –H P0, CHOH SHR + H3PO, Снон +DPNH CHO + DPN COO - H PO, 3 phosphoryl D glyceraldehyde 1,3 diphosphoryl D glycerate DPN is the oxidized form of diphosphopyrıdıne nucleotide a derivative of the B vitamin nicotinamide The mammalian en zyme contains DPN in an enzym itically active form One mole of the enzyme contains two moles of firmly bound DPN Cysteine or another SH compound is required for full activity & At the present time there is good evidence that essential SH groups are involved in the binding of DPN The product of the reaction 13 diphos phoryl D glycerate contains an acyl phosphate bond a high energy phosphate bond (see Table I Chapter II) The acyl or carboxyl phosphate of 13 diphosphoryl D glycer ate is transferred to ADP by the enzyme phosphorylglyceryl Linase CH 0 - H P06 CHO – H PO3 Mg++ CHOH + ADP CHOH + ATP COO-H PO, COOH 13 diphosphoryl- 3 phosphory1 D D glycerate glyceric acid This illustrates how free energy is conserved The enzyme has been crystallized from yeast by Bucher and appears to be specific for all components of the reaction Like other kinases this enzyme requires magnesium ions ·24 Chemisin of Heart Failure (2) Phosphorylglyceryl Mutase Enolase Reactions By the action of these two enzymes 3 phosphoryl D-glyceric acid is con verted to the phosphate ester of enol pyruvate phosphorylenolpy ruvate by the following reactions CH 0 – H PO. CH 0 – H,Pog CH OH CHO – H PO, JP CHO – CHOH H,PO, COOH COOH COOH 3 phosphoryl D glyceric acid 2 phosphoryl D glyceric acid Enolase dehydrates 2 phosphoryl Dolyceric acid to phosphoryl enolpyruvic acid CH OH CH Mg++ ICO - H,PO3 + HO CHO H PO, COOH COOH 2 phosphoryl D glyceric acid phosphorylenol pyruvic acid Both phosphorylglyceryl mutases and enolase have been crys tallized Enolase requires magnesium ions and is inhibited by fluoride shuch forms a Mg F PO, complex that competes 1111 magnesium ions 10 (3) Pyruvate kinase The product of the above sequence of reaccions phosphorylenolpyruvic acid contains an enol phosphate bond The phosplite group is transferred to ADP by private Linase The equilibrium is greatly in the direction of ATP formation ·Chemistry of Heart I ailure 25 CH II CO - H PO, CH Mg++ K+ SC=0 + ATP COOH +- ADP COOH Phosphorylenol Pyruvic acid pyruvic acid The enzyme has been crystallized from human musclell and requires potissium ions in addition to magnesium ions It is quite non specific in its nucleotide requirement in that the diphosphates of adenosine uridine cytıdıne and guanosine can all accept phos phate from phosphorylenolpyruvic acıd? Another importa feature of the glycolysis reaction is the key role played by phosphate and phosphate acceptors such as ADP In glycolysis the metabolism of glucose is tightly coupled with that of phosphate In order for the several reactions to occur phosphate is required as well as phosphate acceptors If the level of ADP falls the overall rate of glycolysis decreases A sudden increase in the level of 4DP as might occur following vigorous muscle activity where large amounts of ATP are hydrolyzed to PO, and ADP could increase the overall rate of glycolysis Such a mechanism might serve to explain how muscle function controls the rate of release of free energy or why after vigorous muscular activity the metabolism of carbohydrates increases hreb's Citric Acid Cycle and the Electron Transport System Since the heart is essentially an aerobic organ13 richly endowed with respiratory enzymes pyruvate is transformed rather rapidly by pyruvic oxidase in the presence of certain coenzymes (thiamine pyrophosphate and lipoic acid) to acetyl coenzyme A 14 Acety1 coenzyme A is a derivative of pantothenic acid and has the follow ing structure 15 In the presence of a condensing enzyme the two carbon frag ment of acetyl coenzyme A is attached to oxalacetate to form citrate thereby initiating a cyclic process of reactions known as hrebs citric acid cycle 16 The net result of this cyclic process is the release of two molecules of co and 8 hydrogen atoms by enzymatic ·26 Chemistry of Heart Failure =C-NH2 HC-N II I-C-N CH 0 HH C-C-C-C- CH2 Η | Ι Η OH H PO3 OH OH CH3 0 ro 1 JIH н н ! -O-P-O-P-OCH-C-CHOH-C-N-CH-CH2-C-N-CH2-CH-S-C- 6 Сн, 1 8 Acetyl Coenzyme A decarboxylation and dehydrogenation respectively Oxilacetate is regenerated to react with another molecule of acetyl coenzyme А (see Figure 2) The CO released can tahe part in fixation reactions' or enter the general circulation It should be noted that carbon never reacts directly with oxygen to forin CO The protons and accom panying electrons enter a series of oxidation and reduction reac tions Inown collectively is the electron transport system This sequence of events is gnen in Figure 3 The proper arrangement of the components in the electron transport system has been estab lished from thermodynamic spectroscopic and chemical considera tions At the level of the cytochromes the protons enter the solent phase and the electrons are transported on by this system to O Oxygen is thereby activated and reacts with protons to form HO The free energy made available by electrons which drop from their high potential at the substrate level in the citric acid cycle to that at the level of 0 1 trapped and conserved in the form of ITP The sum total of these reactions is known asosdatne phos phorylation in contradistinction to phosphorylation at the sub strate level ishuch occurs during the glycolysis reaction From a knon ledge of the potential drop from the substrate level to molecular oygen it is possible to estimate the free energy released durin, this process from the following relation AF = -FE (see Chapter II) ·27 Chemistry of Heart Failure Glycolysis Pyruvate Acetyl COA Cod Oxalacetic Acid Cit ic Acid ci. Aconitic Acid 2H Malic Acid Juocitric Acid Elect on Transport 1 System ZH Fumaric Ac d Oxalosuccinic Acid ZH r 2H 11 COA H2O CO2 CO2 Su cinic Acid Succinyl COA Ketoglutaric Acid ATP ADP +Ph Figure 2 Outline of hreb s citric acid cycle Belitserls showed that the AF for the transfer of a pair of electrons from the substrate level in the citric acid cycle to molecular oxygen was approximately -55 000 cal/mole of oxygen Since the forma tion of 1 mole of ATP requires an input of 12 000 cal it is evident that approximately 4 moles of ATP may be generated in the trans port of each pair of electrons to oxygen providing suitable coupling mechanisms exist Calculationsld reveal that approximately 80% of the total free energy obtained from the degradation of glucose is conserved by ·28 Chemistry of Heart Failure OXIDATIVE PHOSPHORYLATION Subott te Level Electo Tunspt Sytm Kr b Citri Acid Cycle X ADP 1 27 XNPO4 ATP DPN OPNH2 PO4 + FAD FADH2 Cytom (7) ATP •-•--PO4 - Po 1 Cyto hom e Cyt hom a NPO4 Cythema • 1/2 O2 H20 Figure 3 Outline of the electron transport system the process of oxidative phosphorylation The remaining free energy is trapped by phosphorylation at the substrate level The detailed mechanism of the oxidative phospliorylation reaction is not known with certainty at the present time Tlus is probably due to the fact that it has been extremely difficult to 156111e the individual enzymes in a high state of purity Energetic Coneiderations An analysis of the energetics of the following reaction CH, 0% - 60 = 6CO + 6H 0 indicates that the free energy change in olsed in the con crsion of I mole of glucose to CO and I is approximately – 688 000 cal ·Chemistry of Heart Parlure 29 If one N PO, represents a AF byd 1 of – 12 000 cal we have 688 000/12 000 or approumately 57 N PO, theoretically available from the complete oxidation of glucose When glucose is degraded to pyruvic acid some 50 000 cal of free energy are theoretically available: An analysis of Figure 1 will show that in the anaerobic breakdown of glucose to pyruvate a total of four ATP molecules are synthesized Honerer of these four one is utilized in the phosphorylation of glucose and one in the conversion of fructose 6 phosphate to fructose 1 6 diphosphate Hence a net synthesis of only 2 ATP molecules occurs There fore the efficiency is 2 x 12 000 X 100 = 48% 50 000 In the complete oxidation of pyruvate approximately 630 000 cal of free energy are made available Accompanying this process approximately 38 molecules of ATP are synthesized 3 Therefore the efficiency of oxidative phosphorylation would be 38 X 12 000 X 100 72 630 000 and the overall efficiency would be (38 + 2) (12 000) (100) = 700 688 000 Alternative Sources of Energy Recent studies indicate that when the concentration of glucose in the blood falls below a cer tain level the myocardium has the capacity to utilize fatty and amino acids for free energy sources * In fact there is some evidence that the major free energy source for the heart may well be fatty açıds 5 Fatty acid metabolism is of co interest since mole for mole the complete degradation of a fatty acid males available considerably more free energy than glucose breakdown (1) Fatty Acid Metabolism knoop e first showed that fatty acids were degraded by Boxidation from the carboxyl end of the molecule in the following manner C, Cz R- COOHR-CC-COOH-R-COOH

·30
Chemistry of Heart Failure
R CH2 CH2 COOH
COA ATP
(1) Activation
R CH2 CH2-CO COA
FAD
(2) Dehydrogenation
R CH CH CO COA
(3) Hydration
R CHOH CH2 CO COA
DPNH
(4) Dehydrogenation
R CO CH2 CO COA
COA
(5) Cleavage
RCO COA + CH3 CO COA
Krebs Citric Acid Cycle
Figure 4
Outline of fatty acid degradation
It is nous known that in animal tissues all the enzymes neces
sary for the activation and degradation of free fatty acids exist
A typical sequence of reactions is presented in Figure 4
It can
be seen from the figure that in the Boxidation of 1 mole of fatis
acıd only 1 mole of ATP is utilized regardless of the chain length
Once the fatty acid is in the form of the acyl coenzyme i derivatie
the thiol ester group is preserved until it condenses with oualacctate
to enter the citric acid cycle for further metabolisin
The total free energy release accompanying the complete

·Chemistry of Heart Failure 31 degradation of a fatty acid such as palmitic acid has been deter mined The reaction is as follous C&H O +230 + 30H 016CO + 46H O AF = -2 230 500 cal The release of free energy occurs in the major steps (1) palmitic acid = 8 acetyl coenzyme A +34ATP (2) 8 acetyl coenzyme A + 16H 0 + 160 = 16C0 + 24H 0 + 104ATP Thus a total of 138 molecules of ATP are synthesized per mole of this fatty acid metabolized and the efficiency for the process is (138 1) 12 000 X 100 =71% 2 230 500 (2) Amino Acid Metabolism The reversible transfer of an amino group from an amino acid to a Leto acid was first described by Braunstein and Iritsman » This reaction is catalyzed by a group of enzymes called transaminases These enzymes require deriva tives of pyridoxal phosphate as coenzymes Two of these enzymes are of considerable interest and will be discussed briefly as they illustrate how certain amino acids enter the hreb s citric acid cycle (1) Glutamate aspartate transaminase This enzyme catalyzes the following reaction COOH COOH CH2 COOH CH COOH 1 CH, + CH, CH, + CH CH - NH 1 1 C=0 C=0 CH – NH I COOH COOH COOH COOH 1 glutamic acid oxalacetic acid a hetoglu taric acid 1 aspartic acid ·32 Chemistry of Heart Failure (2) Glutamate alanate transaminase the following reaction This enzyme catalyzes COOH COOH 1 CH CH - CH CH, CH CH, CH - NH + c=0 C=0 + CH – NHA COOH COOH COOH COOH 1 glutamic acid pyruvic acid a ketoglu taric acid I alanine The highest concentration of glutamate aspartate trusamındse is found in the myocardium and liver 30 Apparently in severe liver or myocardial diseuse this enzyme is released into the serum and serum levels of this enzyme are thought to measure the extent of damage 31 Summary In the above considerations tle fave seen that the release of free energy by the combustion of foodstuffs in the myocardium occurs in two major phases In the first plase small inolecules such as glucose fatty and amino acids are incompletely metabolized to one of three constituents acetyl cocnzyme A a ketoglutarate or oxalacetate Acetyl coenzyme A constitutes the greater amount Two thirds of the carbon atoms of carboliyelrates all the carbon atoms of the common fatty acids and approximately one half of the carbon atoms of amino acids yield acetyl coen zyme A) The three end products of the first phase are metabolically similar They take part in the second major phase of free energy release the hreb s citric acid cycle and the electron trinsport sys tem The latter systems may be considered as the final common pathu y for the complete combustion of all foodstuffs In Figure 593 we have attempted to summarize in a diagrammatic form the major metabolic events associated with free energy release and its sulise quent trapping in the forn of ITP ·Chemistry of Heart Failure 33 LIBERATION CONSERVATION UTILIZATION (PV) For Act) frecent you Lacto Pet CUT CETO 1 ACTATOS CP CARDIAC FUEL ATP CARDIAC WORK A OA Succ/ MAL FUM P ADP ACTN KYOSN CYTOCHROME o Figure 5 Schema of free energy release conservation and utilization in cardiac muscle Reproduced by permission Olson and Patnel Inn A Y Acad Sc. 1959 Localization of Enzymes in the Cell There are a number of factors that influence the rate of enzymic reactions within the cell These include temperature pH coenzymes redox potentials con centration of reactants and the presence or absence of inhibitors Another extremely important factor is the intracellular organiza tion of enzymes Organization facilitates a rapid utilization of the products of one enzymatic reaction by another The complex series of reactions discussed in the present chapter require participation of many enzymes whose activities are interrelated and coordinated The formation of pyruvate from glucose requires the coordinated and sequential action of at least ten enzymes As a result of this action a portion of the chemical potential energy of glucose is consered Although we are now fully aware that many cell enzymes as well as enzyme systems function quite well in simple solution the living cell cannot be considered to be simply a bag of enzymes Histology and electron microscopy tell us that the living cell has a beautıfully elaborate structure Classically the cell contents have been divided into cell membrane cytoplasm and nucleus The cell cytoplasm is a heterogenous system containing many particulate ·31 Chemistry of Heart Failure structures such as mitochondria microsomes glycogen granules myofilaments and endoplasmic reticulum 31 Due to the development of the technique of homogenization and differential centrifugation by Bensley and Hoers 3 Cluude36 and Hogeboom 3 we have been able to establish considerable infor mation concerning the distribution and localization of enzymes tithun the cell (1) Nucleus It was earlier thought that a number of enzymes were located within the nucleus or on its limiting membrane However modern isolation and purification techniques have estab lished that the nucleus is primarily the center of nucleotide metabo Iism and that all enzyme systems involved in free energy release are absent If the nucleus does play a role in free energy release it is probably an indirect one There is good eudence that nuclear desoxyribonucleic acid and ribonucleic acid control the synthesis of the cytoplasmic enzymes involved in the release of free energy The studies of Vazia3 indicate that the glycolytic and respiratory enzyme systems remain intact for long periods after enucleation (2) Witochondria Vitochondria consume oxygen and con tain all of the enzymes necessary to catalyze the reactions in the Krebs citric acid cycle fatty acid oxidation electron transport sys tem and oxidatne phosphorylation 39 The major role of these organelles in aerobic metabolism and ATP production have estab lished them as the policr houses of the cell Irrei ersible damage 10 isolated mitochondria occurs after periods of ageing inoxsa ind exposure to certain surface active agents ATPase activity usually increases under these conditions and the esterification of inorganic phosphate into high energy phosphate compounds is diminished Los concentrations of certain chemical agents such as 24 dini trophenol and congeners are also knonn to couple oxidate phosphorylation in mitochondria almost completely shule actually stimulating (up to 100%) or having little effect on respiration These agents appear to stimulate an ATPase or phosphritaselile The addition of ATP partially reverses thur action Other uncouplers include azide dicoumarol43 and 1fyroxine" activity 111

·Chemistry of Heart Failure
32
Figure 61
In electron micrograph of rat venucle X50 200 Reproduced by
permi sion Suelesitz in A Y Acad Sci 1999
None of these chemical agents interfere with phosphorylation at
the substrate level as occurs during glycolysis
Vany authors have presented evidence that mitochondria may
function in cellular differentiation' and cell membrane transport
In Figure 6a we have presented an electron micrograph of
typical mitochondria" from heart muscle (sarcosomes) A diagram
41

·36 Chemistry of Heart Failure fc Figure 6L I tri dimensional model of a mitochondrion C crista b branched cristae fc intramitochondrial space o limuting double salled membrane Reproduced by permission Histochem Cytochem 7 188 1993 (Palade) matic sketch is shown in Figure Gb 19 The typical mitochondrion has been shown by a number of investigators Claude ind Fullam ** Dalton 49 Palade and Sjostrınd and Rhodm 'to possess a double walled limiting membrine approximately 80 i thich Invagina cions continuous with the inner of the illo membrınes partially occupy the intramitochondrial space These have been called cristae mitochondriales by Palacle The dimensions of mitochon dria from heart muscle range from 0 3 to 17 u in length and 0 2 to 10 p in diameter It is well known that these particulates have certain osmotic or colloidal properties in that they snell und shrink reversibly in various media 3 Permeability studies indicate a more or less func cional inembrine The dense inner matrix of folded cristie present ? very lurge surface area for adsorption of substrates and metabolic reactions ·Chemistry of Heart Failure 37 The exact localization of the various enzymes in the mitochon drion is not established Upon fragmentation (by sonic vibration or surface active agents) insoluble submitochondrial units have been shown to possess the ability to transport electrons or to medt ate oxidatne phosphorylation 5 Vost studies indicate that the citric acid cycle and fatty acid oxidation enzymes ire in a more soluble state within the intramitochondrial matrix 3 (3) Microsomes Vicrosomes are much smaller particles than mitochondria and sediment in higher gravitational fields Micro somes probably form a part of the fine tubular network in the cytoplasm called the endoplasmic reticulum. These structures contain large amounts of lipids and ribonucleic acids 5 Studies on the incorporation of amino acids suggest that protein synthesis occurs he 59 69 (4) Soluble Enzymes Many of the intracellular enzymes appear to be present in simple solution in the cytoplasm Enzymes involved in the glycolysis reaction are found in the cytoplasmic fraction 6 However for full activity of this multi enzyme system the mitochondrial and microsomal fractions are required 61 Many of the enzymes catalyzing ATP requiring reactions are also in the soluble fraction as well as those catalyzing the urea cycle ? (5) Cell Membrane Two enzymes of great physiological importance are present in the cell membrane at least in the case of red cells and squid axon cholinesterase6 63 which hydrolyzes acetylcholine and an ATPase 66 There is strong evidence that cholinesterase controls the rate of passive transport of cations in excitable tissue of while ATPase is involved in actie transport of these electrolytes 67 REFERENCES 1 Levine R Goldstein M D Huddlestun B and Klein SP Action of insulin on the permeability of cells to free hexoses Am J Physiol 163 70 1950 2 Bing RJ The metabolism of the heart The Harley Lectures 1954 5 New York Academic Press 1956 ·38 Chemisiry of Heart Failure 3 Bing R } Siegal A Vitale AG Balboni, F A Spasks E klapper M and Eduards S Metabolism of the human heart inuo I Carbohydrate metabolism Am J Afed 15 284 1923 4 Ilirburg Ond Christian 1 Isolierung und krisulisation des Proteins des owdierenden Girungsferments Biochem Ztschr 303 40 1939 5 Raphine L Raphine S Mind Trpinac P Effct de la protce tion contre cytosomase des groupes su}flydriles des delydrogen ases Compt rend Soc biol 209 253 1939 6 Racher E and brinishy I The mechanism of action of glycer aldehyde 3 pliosphate dehydrogenase Vature 169 1013 1952 7 Bucher 1 Uber cin Phosphatuber tragendes Garungsferment Biochem et Biophys Icta 1 -92 1917 8 Congill RW and Przer L T Purification and sonic properties of phosphoglyccric acid muise from rublit shcleri muscle Biol Chem 22, 885 1956 9 Warburg and Christian " Isolierung und kristillisation der Enolasc Valuru is 29 589 1911 10 Tarburg und Christian 11 Chemische Wirkun, der Flour deninhibition der Hefe laturu 159 29 390 1911 11 kubowitz Find Out P Isolierung von Garungsfermenten aus menschlichen Muskeln Biochem Zischir 17 193 1911 12 Strominger | L Enzymıc synthesis of guanosine and cytidine triphosphates note on the nucleotide specificity of the pyru 171c phospholinisc rerction Biochem et Bioplys fra 16 616 19.5 13 Bing RJ Castellanos 4 Gridel [ Lupton C und Siegel A Lxperimental myocardial infarction circulatory biochemical ind pathologic changes Am J A Sci 2, 533 1956 11 Reed L ) and DcBush B G Lipothamide and its relation to 1 thiaminc coenzyme required for oxidatile decarboxylation of a leto acids 1 dm Chem Soc 74 3157 1952 1. Lynen F and Reichert L Zur chemischen Structur der alts sierten Essigsaure Ançew Chem 63 47 1931 16 hrebs HA The intermediary stages in thc biological oxidwuon of carbohydrate ddiances En ymol 3 191 1913 17 Oclio S Biological mechanisms of (ubo slation and decirboxy 17tion Physiol Rer 31 56 1951 18 Belitser VA The role of thermodynamics in biochemici intesti gations l'hrain Brokhum Zhur 18 279 1916 ·Chemistry of Heart Failure 39 19 Lelninger AL Respiratory energy transformation Rev Mod Physics of 136 1999 20 Green DC Studies in organized enzyme systems The Harvey Lectures 19567 New York Academic Press 1998 21 Dickens F The En ymes ed by J B Sumner and K Vyrback New York Academic Press 1951 22 Burton hand hrebs H A The free energy changes associated with the individual steps of the tricarboxylic acid cycle glycoly sis and alcoholic fermentation and with hydrolysis of the pyro phosphate groups of adenosinetriphosphate Biochem , 54 91 1993 23 krebs H A Ruffo A Johnson M Eggleston L V and Hems R Oxidative phosphorylation Biochem 1 54 107 1993 24 Bing R J Sregal A Ungar I and Gilbert M Metabolism of the human heart II Studies on fat ketone and amino acid metabolism Am J Med 16 501 1954 25 Visscher M B and Mulder AG Carbohydrate metabolism of the heart Am J Physiol 94 630 1930 26 knoop F Der abbau aromatischer Fettsauren im Tierkorper Bertr chem Phys Path 6 150 1904 27 Dixon M and Webb EC En ymes New York Academic Press 1958 28 Lynen F Acetyl coenzyme A and the fatty acid cycle The Harvey Lectures 1952 3 New York Academic Press 1954 29 Braunstein AE and Kritsman V G Preparation and prelım inary purification of the coenzyme of aspartic aminopherase Biokhimiya 8 I 1913 30 Wroblewski F The clinical significance of alterations in trans aminase activities of serum and other body fluids In Advances in Clinical Chemistry I Ed by H Sobotka and C P Stewart New York Academic Press 1958 31 Burstein ) and Harjanne 1 Glutamic oxalacetic transaminase and C reactive protein in myocardial infarction with special refcrence to the electrocardiographic pattern Acta Med scan dinat 163 175 1959 32 Krebs HA Some aspects of the energy transformation in living matter Brit M Bull 9 97 1993 33 Olson RE and Piatneh DA Conservation of energy in cardiac muscle Ann New York Acad Sc 72 466 1959 ·40 Chemistry of Heart Failure 31 DeRoberts EDP Noru Inskı WV W and Saez F A General Cytology 2nd edit Philadelphia Saunders 1991 35 Bensley R R and Hocrr NL Studies on cell structure by the freczing drying method VI The prepiration and properties of mitochondri Anal Rec 60 4 19 1931 36 Claude A Frontiers of chemistry Biol Symposia 10 111 1913 37 Hogeboom G H Separation and properties of cell components Federation Proc 10 610 1931 38 Mazia D Physiology of the cell nucleus In Modern Trends in Physiology and Biochemistry ed by E S Guzman Barron New York Academic Press 1952 39 Neilands ) Pind Stumpf Pk Outlines of En zme Chemistry New York Wilcy 1935 40 Tyler D B Some factors affecting the action of 2 1 dinitrophenol on the ovygen uptake of excised rat liver Brol Chem 184 711 1990 41 Tepley L J Studies on the cyclophorase system VIV Mechan ism of action of 24 dinitrophenol Arch Brochem 24 383 1919 42 Hunter F E The relationship of dinitrophenol activated adeno sinetriphosphatase to uncoupling mechanisms and possible phos phorylation of electron transfer catalysts Proc Intern Cong Biochem 3rd Congr Brussels 1955 New York Academic Press 1956 43 Martius C and Nitz Litzow D Mechanismen der Vmink Wirkung Brochem Zischt 327 1 1935 14 Judah J D The action of 2 1 dinitrophenol on oxidzie phos phorylation Biochem , 49 271 1971 1. Gustafson T and Lenique P Studies on mitochond in the developing sea urclun egs Exper Cell Research 3 201 1952 46 Batcy Darcs RE and hrebs HA Active transport in animal tissues and subcellular particles Proc Roy Soc London, SB 142 187 1951 47 Sichcuitz P Oxidative phosphorylation in muscle mitochondrit and its possible regulation Ann New Tort Acad Sc 72 500 1959 48 Claude A and Fullam F F An electron microscope study of 150 lated mitochondria | Exper Afed 83 199 1916 19 Dalton A, hahler H hells V1 G Lloyd B J and Strichoch TJ Some observations on the mitochondria of normal and ·Chemistry of Heart Failure 41 neoplastic cells with the clectron microscope | Nat Cancer inst 9 439 1919 50 Palade G C Thc fine structure of mitochondria Anat Rec 114 427 1952 51 Sjostrand rs and Rhodın) The ultrastructure of the proximal convoluted tubules of the inouse kidney as revealed by high reso lution electron microscopy Exper Cell Research 4 5 426 1993 52 Moore DH and Ruska H Electron microscope study of mam mulian cardiac muscle cells Bioplus Brochem Cytol 3 261 1957 53 Raathrub J Die Schwellung isolierter Leberzellmitochondrien und ihre physikalishe chemische Beeinflussbarkeit Helvet physiol et pharmacol acta 11 142 1953 54 Cooper C Deslin TM and Lehninger AL Oxidative phos phorylation in an enzyme fraction from mitochondrial extracts Brochum et Brophys Acta 19 159 1955 55 Chantrene H Heterogeneite des granules cytoplasmiques due foie de souris Biochim et Biophys Acta 1 437 1917 56 Porter KR Observations on a submicroscopic basophilic com ponent of cytoplasm Exper Med 97 727 1953 57 Barnum G P and Huseby R A Some quantitative analyses of the particulate fractions from mouse liver cytoplasm Arch Bio chem 19 17 1918 58 Zamecnik PC and heller E B Relation between phosphate energy donors and incorporation of labelled amino acids into protein) Biol Chem 209 337 1954 59 Siekevitz P Uptake of radioactive alanine in vitro into the proteins of rat liver tractions J Biol Chem 195 519 1952 60 de Duve C and Berthet J The use of differential centrifugation in the study of tissue enzymes Internal Rev Cytol , 225 1934 61 Schneider C Structural factors in metabolic regulations Proc Intern Cong Biochem 3rd Congr Brussels 1955 New York Academic Press 1996 62 Holland WC and Greig N E Scudies on permeability VI Increased permeability of dog erythrocytes caused by cholines terase inhibitors Arch Biochem Biophys 32 428 1951 63 Boell E J and Nachmansohn D Localization of choline esterase in nerve fibers Science 92 513 1910 61 Post RL Relationship of an ATPase in human erythrocyte

·42
Chemistry of Heart Carlure
membranes to the active transport of sodium and potassium
Federation Proc 18 121 1999
65 Libet B Localization of adenosine triphosphatase in the grant
nene fibers of squid Biol Bull 93 219 1917
66 Holland TV C and Auditore GV Effect of acetylcholine on
rate of uptake and equilibrium distribution of physostigmine
in human erythrocytes J Appl Physiol 9 147 1956
67 Skou JC Influence of some cations on an adenosinetriphospha
tase from peripheral nerves Brochim et Brophys Acta 23 391
1957

·Chapter IV CHEMISTRY OF THE NORMAL HEART PART II FREE ENERGY UTILIZATION Introduction In the preceding chapter we have discussed some of the chemical mechanisms involved in free energy release from essential foodstuffs In the present chapter we intend to review the known physico chemical events associated with the utilization of free energy for the performance of work There is now good evidence that the free energy utilizing system in the myocardium is the protein complex actomyosin ATP serves as its major energy source A mere knowledge of the physico chemical properties of actomyosin and its interaction with ATP is not suffi cient to describe completely the events accompanying muscle con traction A coherent and integrated visualization of the events in contraction requires additional information necessary to answer the following questions What is the nature of the stimulus (excitation contraction coupling)? What is the chemical and physical nature of the com ponents actually participating in contraction? What changes occur between the participating components during the shortening process? What is the nature of the physico chemical events whereby the free energy of hydrolysis of ATP is utilized in the performance of mechanical work? The first two questions may be answered with some degree of certainty Numerous models have been proposed to explain the contrac tion process but the subject remains highly speculatie This is only natural in view of the wide variety of techniques and pro cedures employed by investigators with diverse backgrounds Cach has his olin vien point It should be pointed out at this time that the authors have little confidence in chemical theories which make ·44 Chemistry of Heart Tarlure no attempt to account for morphological or plıysiological cient accompanying the contractile response As was mentioned previously the information in the presen chapter in large part concerns skeletal muscle because most of ou Inon ledge has been obtained from studies on this tissue How ever there is little reason to doubt that cardiac muscle is supila to sheletal muscle There are difterences in morphology and chemistry but these are of a quantitive and not of a qualitativniture Morphological Considerations The histological structure o both striated and cardiac muscle as well as changes that occur dur ing the contractile response were well described by 1900' With the rapid advances in muscle chemistry the contributions of the 18th century microscopists were soon forgotten The desclopment of the techniques of electron microscopy x ray diffraction optica rotation and others has stimulated reinvestigation of muscle struc ture and activity The unit of structure in both striated and cardiac inuiscle is the muscle fiber which measures 10 to 100 p in diameter and whose length varies considerably (a fex millimeters to several centimeters) In cardiac muscle there is considerable branching and anastomos ing of muscle fibers guing the appearance of a syncytium (Figure 7) Each branch of the cardiac muscle fiber terminates at an inter calated disc wluch according to recent electron microscope studies represents a portion of the cell border or membrane 3 The inter calated discs are actually continuwions of the inner and functional layer (plasma membrane) of the cell membrane (sarcolemma) Lach disc measures 130 to 150 ( wide It is composed of tho opposing thickened segments of the plasma membrines of two cells separted by a narrou interspace The muscle fiber contains bundles of myofibrils the contrac dile units of the cell The myofibril mestres 05 to 20k in diameter 3 Flectron micrographs shou that there is no boundary membrane separating the myofibril from the various substances in the sarcoplasm free access of substrates coenzymes and sons is entirely probable In Figures 81 ind b typical electron micrographs of striated

·45
Chemistry of Heart Failure
$
Figure 7 in electron micrograph of rabbit myocardium X4800
D inter
calated disc N nucleu z hrauses membrane (Z line) Reproduced by per
mi son J Projhys Biochem Cytol 1997 (Vuir)

·46
Chemistry of Heart Failure
A."
1.
Figure 87 In electron mingtaph of strated muscle (crul miotome
Ambhse na list) 1800 er endoplasmic reticulum i hrauss mein
brane (Z line V V line in II 7onc II band i land keproduced by
I crnisson / Bilis Pochem (tol 191 (I orter and Jala)

·Figure 81) In electron micrograph of rit ventricle X 15 500 er endoplasmic reticulum I band 1 I band H I zone z krauses membrane (2 line) I lipid body Note large number of sarcosomes (mitochondria) between myo fibrils Reproduced by permission ) Diophys Brochem Cytol 19,7 (Moore and Ruska) ·48 Chemistry of Hearl Carlure M Z Figure 9 In electron mictograph of an isolated myofibrul X 50 000 Reproduced by permuassion | Brophos Brochem Cylol 1997 (Husicy) and cardiac muscle3 ure presented! They illustrate the essential structural features as well as the differences which exist in the two tissues Figure 96 is an electron micrograph of an isolated myofibril The cross striations along the long axis of the fibrul are due to differences in optical and staining properties These strations give the appearance of a series of discs or bands lined up side by side The darker or anisotropic regions are referred to as A binds the lighter or 1sotropic regions are referred to as I binds In the center of the I band there appears a thin highly refracule zone (kruses membrue)' called the 2 line 7 lines of adjacent myofibrils are interconnected by continu ous membranes & They appear to diside the whole muscle fiber transiersely but in an ascending and descending step lıhe fashion They eventually merge with the plasma membrane (inner layer of the surcolemma) at the outer border of cach fiber ·Chemistry of Heart failure 19 In the middle of the Abund there is a less dense region called the H zone which is particularly event in stretched fibers In the center of the H zone inother thin region of somewhat greater density is observed The latter is referred to as the line There is some evidence that adjacent M lines are continuous similar to tlie Z lines # The surcomere is the longitudinal unit of the myofibrıl and is delineated by tho 7 lines Therefore it includes one half of an { band at either side of an A bid in heart it is ! I to 24 u long" On closer examination of electron micrographs one can see that each myofibril is composed of a number of myofılaments arranged in parallel (see Figure 9) These are basically of t11o types a thin tenuous filament and a much denser one The thin fila ments begin at the 2 lines extend through the I band into the A band and end in the H zone in the A band the thin I bind fila ments interdigitte with the thicker 4 bind filaments In a cross section (Figure 10) through the 1 band it can be seen that the thin filaments (diameter 40 A) are loc ited in a regular Figure 10 An electron micrograph cross section through band region X 150 000 Reproduced by permission Brophys Brochem Cytol 1997 (Fluxley) ·48 Chemistry of Heart Tarlure Z Z A Figure 9 In electron micro,raph of an isolated myofibril X 50 000 Repro duced by permission | Biophys Brochem Cytol 1947 (Huxley) and cardic muscle tre presented They illustrate the essential structural features as well as the differences which exist in the tho tissues Figure 99 is in electron micrograph of an isolated myofibril The cross striations along the long txis of the fibril are due to differences in optical and stuning properties These striations gue the appearance of a series of discs or bands lined up side by side The darker or anisotropic regions ure referred to as A bands the lighter or isotropic regions are referred to as I bands In the center of the I band there appears a thun lughly refractıle zone (hrauses membrane)' called the 2 line Z lines of adjacent myofibrıls are interconnected by continu! ous membranes & They appear to diude the whole muscle fiber transversely but in an ascending and descending step-like fashion They eventually merge with the plasma membrane (inner layer of the surcolemma) at the outer border of each fiber ·51 Chemisin of Hearl Failure % m 120 S 28M A 150 | 134 100 $ 234 A 150 10811 sec 100 S 234 A 15p 10-8 90 S 2011 A 1541 1051 80 $ 1841 A 15 1 0-3 60 S 144 Figure 11 Diagrammatic longitudinal sections of sarcomeres during stretch and contraction S sarcomere width 4 bund width II band widths elastic component in H zone sec series elastic component near line 1 thuck bind filament a thin I band fuament contraction band Repro duced by permission Symposia Soc Exp Bol 19,5 (Hanson and Huxley) ·52 Chemistry of Heart Inilure These findings led the Huxleys to propose the slıdıng model of contraction to be discussed later in the chapter Chemical Considerations Almost 2 century ago huhne ex tracted a protein from muscle by treating the tissue with strong salt solutions ! He gave the name myosın to his preparation For the next one hundred years the name myosın 7s used to denote the substance or substances which could be extracted from muscle by solutions of relatively high ionic strength in 1930 von Mural and Edsallı showed that these solutions exhibited a strong double refraction of flow suggesting the presence of elongated and rather large molecules During the late thirties and early forties a number of investi gators18 17 showed that ATP had profound effects on the physico chemical properties of myosi On the addition of ATP to myosin solutions the double refraction disappeared and the vis cosity decreased Furthermore threads prepared by squirting myosin solutions into water contracted in the presence of ATP In 1939 Engelhardt and Ljubimoszt showed that myosin con cained ATPase which split off the terminal phosphate of ATP forming free phosphate and ADP Thus it was only natural to assume that these reactions might be the chemical basis of muscle contraction In the early forties it was discovered that classical myosin was in reality a mixture of two proteins myosin and actin" Icon exists in the forms 'globular or Gactin and 1 fibrous or I 1011 F actin interacts with myosin to form a neu protein actomyosin Thus the myosin of huhne c?n be considered to be actomyosin From the many sided evidence accumulated in the last hfiecu yeirs these discoveries encompass 1/1 that seem basically essential in the chemistry of muscle contraction thit is myosin acting as an 4 TPase ctin and ATP (1) Wyosin 18 The protein myosin can be extracted from muscle with about half molar salt solution at pH 65 It has 3 molecular weight of the order of 400 000 10 120 000 Wyosin is an elongated particle being approximately 1600 X long and 50 i wkle Well purified myosini splits the terminal phosphate group of ATP ·Chemistry of Heart Failure 53 and related nucleotides Vyosin ATPase is activated by calcium ions and inhibited by magnesium ions By the action of trypsin each myosin molecule can be degraded into one heavy fragment (H meromyosin) and tuo light fragments (L meromyosin) · The heavy fragment possesses all of the ATPase activity There have been only a limited number of studies on the physico-chemical nature of heart contractile proteins According to Gergely myosin obtained from heart muscle has essentially the same molecular weight and shape as that of skeletal muscle and its reactions with 4TP are similar However Ellenbogen and collaborators present values for the molecular weight of myosin which are considerably less (223 000) The ATPase actity of heart myosin is about one third that of skeletal muscle myosin and it appears more resistent to trypsin and chymotrypsin degradation (2) Actin 19 ° Actin is an unusual protein in that it exists in two forms a globular and a fibrous form. Gactin has a molecular weight of approximately 70 000 and contains approximately one mole of ATP per mole of G actin G actin readily polymerizes to form Factin Only the latter is capable of specific interaction with myosin Upon interaction ATP is split into ADP and inorganic phosphate (3) Tropomyosin Tropomyosin comprises approuimately 4% of the myofibrıllar protein and it has been crystallized by Bailey At low salt concentrations tropomyosin exists as a highly viscous thread in solution it is largely depolymerized at 0 16 M KCI (intracellular concentration) and has a particle weight of 120 000 Actin and tropomyosin combined have a similar amino acid composition to myosin in all species tested « Tropomyosin has been interpreted as a precursor for some subunit of myosin an elastic component of the myofibrıl and as the substance in cross bridges (1) Della Protein Delta protein 8 a 30 can form a complex with myosin and cause dissociation of actomyosin It is believed to be a derivative of actin and may serve as the underlying struc tural component which facılıtates proper orientation of actin myosin and tropomyosin in the myofibril It may also represent as ·54 Chemistry of Heart Failure MYOSIN ACTIN ACTIN TROPOMYOSIN+(A and 'X'?) PROTEIN Z M A Figure 12 Gencial distrslition of the myofibrallar proteins m the streamer un elastic component (Sfilaments)'s in the H zone At leist part of the 15% of myofibrıldır protein wluch remains after extration of myosin un ind tropomyosun is believed to consist of delta protein Figure 12 diagrammatically illustrates the general costribution of the myofibrillar proteins in the sarcomerc Interaction of Actomyopan and ATP 1 Ictomyosin 15 forned readily by the reacuion of Fictm and myos. The viscosity of actomyosin solution is inych lugher than the sum of the sascosities of the two indadural components Ictomyosin ATPase activity is activated by both magnesium ions and calcium ions In the presence of magnesium ions its activity far exceeds that of anyosin Striking physico-chemi il changes are induced when ATP is added to solutions of actomyosin or in actomyosin threads The double refraction of flou disappears and the viscosity of the solu cions decreases markedly ITP causes contraction of the thread ·Chemistry of Heart Failure 55 These changes have been interpreted as resulting from the action of 1TP to dissociate actomyosin into actin and myosin Relaxing Factor The existence of a surcoplasmic component in muscle which could induce relaxation in isolated systems was first shown by Varshl und Bendall 3 They and other workers have tried to identify this component with various phosphate transfer ring enzyme systems such as myokinase creatine phosphokinase and phosphoenol pyruvate pyruvic kinase All of these transfer phos phate to ADP and their relaxing effect is activated by Mg ions and inhabited by Ca ions The fact that muscle ATPase activity is depressed concurrently with the relaxing effect suggests a direct correlation of the former with tension development Recent evidence indicates that relaxation depends on a criti cal level of ATP in the center of the muscle fiber which could be effected by any of the enzyme systems mentioned However in single muscle fiber preparations these systems do not always cause relaxation and may increase tension of the ATP concentration 15 low enough It is now believed that the relaxing system consists of at least two components a particulate component and a dialyzable labile substance which is readily absorbed on charcoal Neither of these is one of the transphosphorylatin, systems mentioned Pyrophosphate muy replace the dialyzable factor but it is not identical with it The answers to the important questions of whether such sys tems are operable in intact muscle and especially in the myocardium are only speculative Localization of Contractile Proteins Muscle In recent years with improvement in physical and chemical techniques there have been a number of attempts to relate the molecular compon ents of muscle with the ultrastructure of the cell and the actual process of contraction The most elaborate of these studies have been those of H E Huxley & 11 13 13 A F Huxley? 34 and collabo rators By the use of optical and electron microscopy ray dif fraction techniques and specific chemical methods for extracting various proteins from isolated muscle fibers they reached the fol lowing conclusions about the distribution of contractile proteins ·56 Chernisty of Heart Failure Striated muscle (including cardiac) is built up of tio oser lupping interdigitating myofilaments One is a set of thin fila ments extending in either direction from the Z line to the boundary of the H zones and the other is 7 thicher set extending from one end of the A band to the other When muscle fibrıls are treated with solutions that are knonn 10 remove myosin 60 to 70% of the protein material is selectively removed from the 4 band Approxı mately 70% of this protein is actually myosin the remainder is protein 35 The material or myofilaments left are the thun filaments which extend from the Z membrane to the former border of the H zone When the treated myofilaments are examined with the electron microscope the thick filaments which formed the A band are missing and only the thin filaments remun When the myosin extracted preparations are treated with solutions that remore actin an additional 15% of the original myofibrıllar protein is removed The fibrils lose all their visible material between the 7 lines and the H zones The 7 lines and some substance (delta protein?) which muntains structural integrity remain Thus 1 remarhably simple picture emerges of two overlapping sets of faliments built primarily from two structural proteins actin and myosin The thin filaments are composed of zein and the thich dense filaments are composed of myosin Neither citends through the entire length of the surcomere The thun filaments are present both in the I and part of the A binds the thick foluments are in the A bind only The two interdigitate in the 4 bund Suchi a system gives the bunded appearance to the inuscle fibril A number of recent stuclies suggest that the A bud contains ATP and mıny of the enzymes essential for oxidative phosphory] tion independent of muscle mitochondria 36 Theories and Vodels of Muscle Contraction At the present time there are the basic theories that attempt to correlate the molecular and physiological esents accompinying the contractile response The first may be called the one filament hypothesis of the flexible polyelectrolyte theory The second may be called the tho filament lrypothesis or the sliding model of muscle contrac tion. The first attempts to correlate data obtained from studies ·Chemistry of Heart Failure 57 of the chemistry of contractile proteins while the latter attempts to correlate information attained from physical studies of muscle with limited number of chemical observations In the one filament hypothesis contraction is considered to result from physico-chemical changes in a contractile unit consisting of a single filament or molecular strand The clearest and earliest statement of this hypothesis was from a H Meyer 37 He proposed a number of models in which attraction and repulsion of charged groups on a helix were responsible for contraction and relaxation The concept has been developed in a more quantitative manner by Riseman and hırknood38 and later by Morales 39 Molecular chains may extend from one Z line to another Assuming free rotation about chemical bonds and some internal flexibility the chun would tend to form a coil (see Figure 131 b -N- Mg+*- (a) + (ĀTE Mg* (ATP) (d) Mg++- ATP Ru Mg++ (b) (c) Figure 13 Schema of the one filament or polyelectrolyte model of contrac tion Reproduced by permission Peuters of Alodern Physics 1959 (Morales) ·58 Chemistry of Heart Failure (d) 39 Honever if charges were distributed along the fiber the tendency to form a coil (entropic forces) would be opposed by an electrostatic force tending to maximize the distances between charges The resting state or equilibrium is represented by a bol Ince between entropic forces tending to shorten the filament and electrostatic forces tending to keep tlie molecular chun extended Magnesium calcium or potassium myosinates might be so ex tended Contraction or collapse of such a polyelectrolyte is thou,lit to be the result of a discharge of the fiber by the quadrnnlent mions of ATP The resting state is restored by hydrolisis and disorption of ADP Inherent in the polyelectrolyte model is the issumption that the adsorption of ATP and not its hydrolysis is the driving force responsible for changes in the physical properties of the Izlament One of the main objections to such a model is the difficult in explaining the observation that apparently one molecule of ATP can affect as much as 10 g of myosin This seems to be 100 large a sphere of action for electrostatic forces It prompted Szent Gyorgy) to invoke long range quintum mechanical forces of energy transmission and excitition He proposed that in the resting state actomyosin contained stable filled electronic energy levels winch were separated from higher unfilled electronic energy levels (semi-conductor) Upon interaction with ATP certain stable elec trons were excited into the high i acant energy levels (conducting level) The spread of this event caused the whole structure to become excited to depolarize and to go into the contracted state Another shortcoming of the polyelectrolyte theory is that it fails 10 take into account the heat work generalization of Hill" and Fenn' It is for this reason that it should be discarded its simplest form The isso {ılament or sliding model operates on a radically chil ferent principle ** This model atteinpts to take into 1ccount olcs sations on the organization of proteins within the snizofibrıl and the morphological changes fuch occur during contraction Sciter! 111 its simplest form upon excitation the thin filaments in the 1 band slide past the relinely fried thick filaments in the 1 band Illien the muscle is passicly stretched the I bind filiments slide ·Chemistry of Heart Failure 59 out again This hypothesis is in keeping with the observation that the width of the A bind remuns essentially constant at different degrees of stretch and contraction and that the changes in sarco mere length are primarily due to changes in the width of the I band (see Figure 11) This directed slıdıng motion during contraction is presum ably brought about through the mediation of cross links between the filaments Such interaction is the structural basis for the reac tion between actin and myosin It is proposed that ATP reacts with the cross linhages and enables the two filaments to crawl or slide past one another One of the problems with this model is that during contraction it does not explan why the filaments slide only in one direction and not in the other The reaction scheme is actually quite symmetrical Huxley attempts to solve this problem by invoking 1 spatially asymmetric probability of reaction between the sliding filaments Recently Podolshyt has attempted to resolve the differences between the two major theories He accepts the basic sliding model of the Huxleys but assumes that the thin actin filament is a poly electrolyte If discharged the actin filament would coil or fold as the result of entropic forces thereby causing the filaments to slide past each other He reasons that at rest the actin fılament is a positively charged polyelectrolyte and upon excitation some sys tem is activated which deposits ATP molecules on the actın fila ment This discharges the filament and it begins to contract develop tension and draw the two Z lines together Simultaneously the ATPase on the relatnely fixed myosin filament begins to pick off the 4TP molecules which tends to restore the charge on the actın filament Therefore the tension developed and the energy released will reflect an equilibrium between the charging rate and the rate of ATPase activity. This in turn is a function of the rela the velocity of motion between the interacting sites on the two filaments The models of the Huxleys and Podolsky predict that the work output developed during muscle contraction should increase with a decrease in the relative motion between the two filaments (greater probability of interaction between sites) In this manner ·60 Chemistry of Heart Failure they take into account the well known relationships established by Fenn and Hill for intact muscle However neither model accounts for the heat of activation of the contractile process It is well known that in increase in the initial length of the myocardial fiber ss paralleled by 33} increase in the energy of con traction Thus it is probable that the initial length determines the velocity of contraction and thereby the excent of interaction betn een sites on the two filaments REFERENCES 1 Foster M d Text Bool of Physiology 5th edit London Mac millan 1888 2 Muir A R An electron microscope study of the embryology of the intercalated disc in the heurt of the rabbit | Bioplus Bio chem Cytol 3 193 1957 S Moore DH and Ruska H Electron microscope study of mim malıan curdiac muscle cells J Biophys Biochem C1101 3 261 1957 4 Perry S V The components of the myofibril and their sclarion to its structure and function imposia Soc 1 eper Biol 9 203 1955 5 Porterk Rand Pal de GE Studies on the endoplastic reticulum Ul Its form and distribution in suriated muscle cells I Biophys Brochem Cytol 3 269 1937 6 Hurley HE The double arr iy of filaments in cross strinted muscle 1 Bioplus Brochem Cytol 3 631 1937 hrause 1 Die motorischen I ndplatten der quergestreiften Vus kelfasern Hannover Hahn 1869 8 Draper MH und Hodge 1 Studies on muscle with the cloc tron microscope I The ultra structure of tord striated muscle Australian J Exper Biol c V Sc 27 165 1919 9 Bennett HS and Porter KR An electron microscopx sturly of secuoned breast muscle of the domestic fond Am ) Anal 93 61 1923 10 Il einstein II į An electron microscope study of cardiac muscle reper Cell Research 7 130 191 II Hanson ) and Huxley 11 E Structural basis of contrition 11 strued muscle Symposia Soc. Ieper Brol 9 229 1970 7 ·Chemistry of Heart Failure 61 12. Huxley A F and Niedergerhe R Structural changes in muscle during contraction Mature 173 971 19. 1 13 Huxley HE and Hanson ) Changes in the cross striations of muscle during contraction and stretch and their structural inter pretation Valure 173 973 1954 14 kuhne W Untersuchungen uber Bewegungen und Verander ungen der contraktilen Substanzen Arch Inal Physiol z 15$ med Liep ig 564 1859 15 von Muralt A L and Edsall J I Studies in the physical chemis try of muscle globulins III The anisotropy of myosin and the angle of isocline | Biol Chem 89 315 1930 16 Necdliam J Shen SC Needham D M and Lawrence ASC Myosin birefringence and adenylpyrophosphate Nature 147 766 1911 17 Engelhardt WA and Ljubimowa M N Myosin and adenosine triphosphatase Nature 144 668 1939 18 Szent Gyorgyi Aed Stud Inst Med Chem Seged Tols 111 1911 3 19 Bailey Muscle proteins Brit M Bull 12 183 1956 20 Hodge AJ Fibrous proteins of muscle Rev Mod Physics 31 409 1999 21 Szent Gyorgy A Chemical Physiology of Contraction in Body and Heart Muscle New York Academic Press 1953 22 Gergely J Muscle proteins and cnergy utilization Ann Neu Yori icad Sc 72 538 1959 23 Ellenbogen E Izengar R and Olson R E Properties of myosin from normal and failing dog hearts Tederation Proc 18 221 1959 24 Tsao T C The molecular dimensions and the monomer dimer transformation of actin Biochim et Biophys Acta 11 227 1953 25 Barley Tropomyosin a new asymmetric protein component of the muscle fibrıl Brochem J 13 271 1918 26 Kominz DR Hough A Symonds rand Lakı k The amino acid composition of actin myosin tropomyosin and the mero myosins Arch Biochem 50 148 1954 27 Philpott D E and Szent Gyorgyi AG The series elastic com ponent in muscle Brochim et Biophys Acta 12 128 1959 28 Amberson 1 R White J I Bensusan H B Himmelfarb S and Blankenhorn B E A protein a new fibrous protein of skeletal muscle preparation dm Phys10! 188 205 1957 ·62 Chemistry of Heart Failure 29 White ) I Bensuisan HB Himmelfarb S Blankenhorn B E ind 1mxrson WR protein 2 nou fibrous protein of skeletal muscle properties im J Physiol 188 212 1957 80 Bensusan HB 11 hute } I Himmelfarb S Blankenhorn B E and Amberson WR protein a new fibrous protein of shelct: muscle complex formation with myosin Am Physiol 198 219 1957 31 Minrsh bB 1 factor modifying musclc libre synacrusis Valure 167 1065 1951 32 Bendall h Llicct of the Mursh Factor on the shortening of muscle fibre models in the presence of adenosine enphosphate Vatnie 170 1058 1952 33 Huxley HE Ultra structure of striated muscle Brill Bull 12 171 1056 31 Huxley AF Interpretation of muscle striation (udence from visible light microscopy Brit A1 Bull 12 167 1966 35 Seent ( yorgyi A G Mazia D and Srcnt (yorgy: 1 On the enzyme nature of the cross striation of body muscle Biochim el Biophys Acta 16 339 1955 36 Bergman RA tud Taller Do Thic cytochenu u localır ihon of oxidative enzymatic activity and glycogen in fron strited mus. cle Bull Johns Hopkins Hosp 104 179 19.9 37 Veyer hH Uber Feinblu Festigkeit und kontrakultit Turis cher Geriche Brochem Zische 214 259 1929 38 Rosemun / incl hirhnood IC kemarks on the physico chiemi cal mechanism of muscular contriction and reizxation fin Chem Soc 70 2820 1918 99 Morales VF Mechanisms of muscle contracuon Ret Tod Pimsics 31 420 1999 40 Szent (Forg A Bioenergetics Mens Tork Academic Press 1997 Hill IV I he heat of shortening and the dynamic constants of muscle I roc Roy Soc London s B 126 136 1938 12 bonn I he re!ition betucen tark zucrlamed and cherk? libcrtu in muscular contraction / 115101 5987 1921 13 Hayley 1 Vuscle structure and theories of contraction Prog in Brophysics and Biophys Chem 1 239 1937 11 Podolski RĮ The chemical thermodynimics and motor mechanism of muscular contraction ann leu Jork frad 72 522 1929 ·Chapter V CHEMISTRY OF THE NORMAL HEART PART III ELECTROLYTE METABOLISM Ion Transport Another aspect of the chemistry of the heart which has received considerable attention in recent years is the transport and accumulation of electrolytes The heart is similar to other tissues in that the intracellular potassium concentration (h) is relatively high and the sodium (11,) and chloride (CI) concentrations are low There are very good reasons to believe that the quantity of k or Na within the cell is the result of two fundamental unin directional processes an inflon (influx) and an outflos (efflux) "The quantity of h in the cell may be stated in a rather simple mın ner by the following relation dh, dt =kh-kh, where dh,/dt is the quantity of h in the intracellular phase at any time th, he defines influx and I h, defines efflux When the con centration of k in the extracellular phase (k) and h, are unity the transfer coefficients h, and I are the rates of influx and efflux respectively During the steady state when h, remains constant the differential dk,/dt = 0 and efflux equals influx provided all h, is exchangeable The influx and efflux of k may have ictive or pissive com ponents or both Active indicates that metabolism is involved or that ions are transported against or in excess of an electrochemical gradient Passive indicates that the drivin, force is simple diffusion or a fuorable electrochemical gradient In heart recent studies hoe shown that efflux is essentially passite while k influx has both passive and active components 3 At lou k (1 35 mM or less) 63 ·61 Chemistry of Heart Failure h influx appears to be purely passive in response to an actre extrusion of N? At hugher concentrations of active transport components of influx are stimulated Studies using helium cocaine and changes in temperature shon that at 5 4 to 108 mm ho approu mately 430, of k influx is active and 57% 15 passare The chemical mechanisms involved in passate trinsport or in the preferential accumulation of h and extrusion of Va are not Inonn at the present time There is good evidence that oxidatne metabolism maintains actre transport by 1 ay of high energy phos pliate compounds in particular ATP In recent years two specific enzymes have been implicited in cation transport ATPase and cholinesterase The latter enzyine hydrolyzes the chemical transmitter acetylcholine Slous luas studied in ATPase isolated from Carcinus maenas nerve He shoned that the substrate most readily attacked by the enzyme was a sodium magnesium 4TP complex An increase in the concen tration of Na or a decrease of k led to an increase in ATPase activity He reasoned that as Na, increased or K, decreased active transport mechanisms were stimulated The relatively large hyd olyu was necessary to drive the process since acuve transport was essentially an endergonic reaction Vore recently Post has suggested that a membrane ATPase as part of an actue trinsport carrier in the human erythrocyte There is not good endence that cholmesterase plays a role in passie electrolyte transport and thereby is intimately involsed in the genesis of the electrical properties of excitable tissue Acetylcholine the substrate for thuis enzyme has long been known to affect the passtie electrical and permeability properties of the heart It is interesting to note that 50% of this enzyme is located ia the L meromyosin fragment of in osin Barrnett and Palades suggested that thus enzyme was localized in the V line The signifi cance of these observations is not obvious at this time it should be recalled that ATPase was associated with the II meromyosin fragment ATPase and cholinesterase both catalyze hydrolytic reactions and have been localized in cell mumbranes Whether these to enzymes are part of a large molecular complex (myosin like see AF ·Chemistry of Heart Failure 65 above) in the membrane which transports electrolytes is not known with certainty at the present time If it existed such a complex could be referred to as 1 cation transport particle analogous to the electron transport particle isolated from mitochondria by the action of sonic sibrations or detergents (Chapter 3 Mitochondria) In Table lI we have summarized analyses for several important electrolytes in striated cardiac and smooth muscle 11 Cardiac tissue contains more water sodium and chloride and less potassium than skeletal muscle This suggests a larger extracellular space The concentrations of magnesium (Mg) and calcium (C1) in the heart tre comparable to those of other tissues Most evidence indicates that intracellular calcium exists in 1 bound unionized form 1 15 The distribution of electrolytes in nodal tissue atria and ven tricles differ The analyses of Davies et al 16 and Mazel and Hol land'? show that the nodes and AV bundles appear to have 1 sur prisingly large cation excess which is primarily due to the large amount of Na, Mazel and Holland concluded that the intrinsic rhythm of the various regions of the heart was directly proportional to their la content and inversely related to their h content Isotope studies hue revealed that myocardial , Cl and Mg are completely exchangeable within a period of 2 to 4 hours while Na exchanges at a somewhat slower rate? 18 Ca exchange is of a very slow heterogeneous type and cannot be characterized in a simple manner 13 i This suggests that ca exists in several different forms or compartments TABLE II FLECTROLYTE DISTRIBUTION I SKELETAL CARDIAC AND SMOOTH MUSCLE $keletal (Dog) mFq/Liter Gad (D0%) Stomach (Steer) HOU- Na 20 K. 96 80 (0) 39 91 30 3F 8 96 16 CL. 16 Mg 15 2 2 ·66 Chemistry of Heart failure The intracellular distribution of these ions withm the myo cardial fiber is still a matter of conjecture Mitochondria contun hind smaller mounts of V2 Míg und Cz Histochemical studies hre shown that his localized in the A binds of cardiac and strated muscle Upon excitation of muscle ? redistribution of h occurred and the ion moved from the A binds into the I bunds und iccum luted at the cell surface Microincineration studies # hare localized Cr and/or Mg in membranes 4 bands and 7 lines but not in the I bands Electrolytes and Cardiac Contraction That clectrolytes rre essential for ind modify <ardia contraction has been known site the time of Ringer Heuts perfused with isotoma 171 solutions mpidly cease to beat and remun in diastole s The addition of a delnys the 11 effect ud tempor rily restores cadene contraction Chin the absence of h increases the duration of mechanical systole at the expense of dizstole ind eventuully produces a contructure k in excess prolon,s diastole and causes inhibition and arest It is not known that normal ordinc excitation and contraction requires a Vi mnd (1 in appropune concentrations \125 involved in the process of excitability and depolarization h detta nimes the magnitude of the nestin, potentul and ( 7 plus 7 role in excitability and excitation contraction couplin, Bioelectric Potentials In the restin, state a potential differ ence crists between the inside ind outside of all cratible cells the interior being negative wuth respect to the exterior 7lirs potential referred to as the resting or membrınc potential is extul> Irshed across 7 thun barrier (plasma membrane) the thu hness of nach is of the order of 50 40 200. The heart is no excepro and resting potentials of 70 to 80 millivolts have been recorded from single cells in various types of myocardıil tissue 43 A typical transmenbrune resting and action potential recorded froin 7 suigle atrul and ventricular cell ure presented in Figure 11 These jxxentius liere recorded by inserting ? capillary glas uttı? HUCIO clectrode (05 1 0 4 tip diameter) filled with 3 V1 Clinto single myokardulcells There are distinct fertures of the transmembrane resting and action potentials thit requne description The rising phrase or ·Chemistry of Heart I ailure 67 +30 А B OS KPI Imy) Depol- + Repol 80 Jooms 100 ms Figure 14 Typical transmembrane potentials recorded from a single atrial cell (1) and ventricular cell (B) Em membrane potential in millivolts ms millisecond Depol depolarization Repol repolarization Os overshoot 11 plateau upstroke is referred to as depolarization That phase where the sign of potential difference is actually reversed is called the over shoot At the pezh spike potential repolarization begins with an initial rapid phase followed by a plateau where the potential is nerrly zero and terminates with a faster phase of recovery Thie plateru is particularly evident in ventricular cells Figure 15 shows a transmembrane potential and surface ECG recorded simultane ously from closely adjacent sites It can be seen that the QRS complex coincides with the upstroke and initial phase of repoları zation of the transmembrane action potential The isoelectric line coincides with the plateau and the T wave with the terminal phase of repolarization There is not good evidence that the resting potential of excitable cells results from an asymmetric distribution of K and a membrane selectively permeable to h ions The membrme is relatively impermeable to other ions In electrochemical terms the cell may be pictured as a h electrode The magnitude of the resting membrine potential can be estimated from the Nernst equation ·68 Chemisin of Heart failure -80 n t QRS T Figure 15 A typical transmembrıne potential and LCG recorded simultane ously from ndjicent sites E2 303 RT к, log where Er is the resting potential or the k equilibrium potenti R the gas constant F the fıraday n the vzlence und T the absolute temperature When the appropriate units ire substituted at 37 C the equation reduces to Em = 61 millivolts log hy K The ratio h/h, is of the order of I 16 to 1 22 in heart muscle which give alculated values of Ed of 73 to 82 millasolts The measured E. is usually less than the calculated value: This made cates that the resting membrane is permeable to jons other than h such as Ni and CI 33 Upon excitation the membrane suddenly becomes much more permeable to N? ions than to k or Clind the cell momentarily becomes 7 11 electrode is a result of the opposite oricuitation of the Nigridient the interior becomes positie (overshoot) with ·69 Chemistr of Heart failure respect to the exterior The membrue potential gradually returns to that of the resting state (h electrode) by an initial rapid inacti? tion of the inrush of Ni in increased out ard movement of Lions and possibly by an inward movement of Cl ons All three of these processes acting singularly or in combination will restore the potential to that of the resting state Apparently in the heart the plateau results from a delayed inactivation of the inrush of Nz or a delayed increase in outward movement of k or a combination of both It is thought that the duration of the refractory period is determined by the ease of which the inward movement of Na is turned on (availability of the inward Na current) and the rate at which the outward movement of a restores the membrane potential to the resting level During the interval between each action potential the normal Na, and b, are re established by active transport mechanisms Excitation Contraction Coupling The Nature of the Stimulus The mechanism whereby the action potential propagated along the muscle fiber surface activates the contractile elements is not known with certainty There is no question that 1 depolarızation or decrease in resting membrane potential is one of the prime factors involved Hon this event penetrates into fibers and myo fibrils to excite the myofilaments is certainly not clear It is well known that accompanying activation there are distinct changes in the mechanical properties of the muscle before there is any external sign of tension development These changes are character ized by an increase in muscle stiffness resistence to stretch increase in optical transparency increase in pH latency relaxation and heat of activation 34 Whether these changes represent the association of actin and myosin adsorption of ATP mobilization of ions (Ca h Mg) or hydrolysis of ATP is a matter of speculation During recent years a number of theories all involving electrical forces have been proposed to account for some of the changes observed (1) Electrochemical Gradrents and Diffuston On numerous occasions there have been attempts to explain the events of excita tion by assuming the occurrence of diffusion of some essential sub stance such as Ca k or Na from the membrane to the sarcoplasm ·70 Chemistry of Heart Farlure These theories all based on diffusion suffer from a common defect diffusion is not rapid enough } (2) Z Line and Ca dotiation Linkage Recent studies dis cussed in the preceding chapter indicate that the striations of skeletal and heart muscles are specialized to permit the action of depolarization at the surface to be transmitted quekly inward ro the center of the fiber Tiegye in 1934 postulated that the 7 line may transmit surface membrane excitation into the interior By placing fine electrodes along different points of the sarcomere Huxley and Taylor 38 shoned that only depolarization along the I line wis effective in causing shortening of the I band They pointed out that the extent of spread of the contruction in the ? bund was directly proportional to the degree of depolarization This suggested a graded spread of the excitatory process from the 7 line and possibly along the thin utin filaments in addition only cert un loc dlong the conunuous / lines were sensitive to depolarization Bianchu und Shanes proposed that certain sensite patches along the Z line corresponded to sites siturited with culorum which was released into the sarcoplasın during excitation The quantity and rate of release and its subscquent diffusion longitudinally in the I band my wel be related to the magnitude of depolarization It was pictured as a chain reaction Calcitim is the only known plıysiological con that (niscs shortening when injected into the muscle fiber nt lou concentri trons 39 Since there is ourence inot Ca is lacking in one I bam is not unreasonable to assume that the sudden appearic of ionized Cu in this region could either alter the charge or lend 10 3 deposition of ATP on the then actin myofilaments (Podolsky model) The latter may cause these filaments to fold or oil into the 1 band though there is no experimental evidence for a translocation of Ca in the sarcoplasın during excitation there are considerable dati which show that stimulation increases (1 inflon The fact that there is (1 710 ble in die hond suggests that the release of the son lucre might permit interiction with the por tion of the thin clin filaments which overlap the thicker myosin 1 ·Chemisin of Heart Failure 71 filaments and eliminate the necessity of diffusion into the I bind As the I bund filaments are drawn into the Aband more interaction can occur As early (3) Endoplasmic Reticulum as an excitation Conduction Met icorh Brief mention las been made of the presence in the sarco plasm of a fine tubular or vesicular network clearly revealed by electron micrographs called the endoplasmic reticulum as 1881 Retzius suggested an excitatory function for the latter Porter und Paladesl proposed that the membrane component of the tubular network might behave as typical cell membranes and relay the action potential from the sarcolemma into the interior of the fiber In herrt Moore and Rushat have shown that the endo plasmic reticulum appears continuous with the Z lines and extends to intracellular projections of the plasma membrane The reticu lum may not only serve to transmit impulses transversely from the plasına membrane to the Z lines but also longitudinally along the myofibrils to the intercalated discs + 13 REFERENCES 3 1 Kauman Rand Lieclermin PH Lrun potassium cxchange in normal ndult and immature rats am 1 Physiol 175 263 1993 2 Holland WC and hlein RL Cffects of temperature Nz and k concentration and quinidine on transmembrane flux of K+ and incidence of atrial fibrillation Cuc Research ( 516 1938 Holland w Chlein RL ind briggs I H Factors affecting uction of cetylcholine on transmembrane flux of 1n isolated rabbit urnt Am | Pliosiol 196 478 1939 1 Schatzmann II J Herz, lyhoside als liemmstoffe fur den aktuen halium und Naturumtransport durch die Erythrocytenmem Isrun Ielu physiol et pharmacol Acta 11 316 1953 5 Skou JC I be influence of some cations on an adenosine tri phosphatase from peripheral nerves Biochim et Bioplys Acta 2, 391 1997 6 l'ost RL Relationship of an ATPase in human erythrocyte membrines to the active transport of sodium and potassium Tederation Proc 18 121 1959 ·72 Chemistry of Heart Failure 7 burgen ASV and I crrou a G On thc negative inotropic effect in the cits curicle Physiol 120 149 1998 8 Holland WC Dunn CE and Greig ME Studies on perme ability VII Role of acetylcholine metabolism in the genesis of the clectrocardiogrım Am J Phasol 170 939 1952 9 Varga I Cholinesterase activity of contractile protein Zhur Abshchei Biol 20 3 1959 10 Barrnet R } und Palade GŁ The M band cnrımc / Histo chem and Cytochem 6 396 1938 11 Manery ) F Water ind cicctrolyte metabolism Phasol la 4 331 1954 12 Chambers Rund k10 CI The clfcct of electrolytes on the physical state of the nerve axon of the squad and of stentor 1 protozoan Crper Cell Research > 561 19,2 13 Harris [ ] The output of C7from frog muscle Biochem el Biophus dcta 33 80 1957 14 Hodgkin AL and hencs RD Movenients of labelled calciun in squid grunt zxons / Plusio! 138 203 1997 15 Sehul A A inel Holland TIC C138 and C++ cyclinge in ur fibrillation 4m J Physiol 197 752 1959 16 Ducs Dues RL Trancis E TI and 11 hittim R I he sodium and potassium content of cardic and other orsstres al the ox / Physiol 11$ 276 1952 17 Muzel P and Holland WC Acetylcholinc mod clectrolyte metabolism in the various chambers of the frog ind turtle heire Circ Research 6 684 19,8 18 Klein RL and Holland WC Mziundh exchange in atrial fibrillation Am | Physiol 193 239 1938 19 Rayner B und Tlentherall M Digoxin oltabun and potassium movements in rabbit auricles Bot ] Pharmacol 12971 1937 20 Rogers T A and Mahn P E Exchange of radionic Vg in the rit Pror Joc Erper Biol Med 100 239 1959 21 Bianchit P and Shines A V Calcium infini in skeletal muscle at rest during actisit; ind during potassium contructure j Gen Physiol 42 803 1939 92 Griswold RL und Pace I le intracellular distribution of metal ions in rat her loper Cell Research 11 362 1951 23 loerdemann VI Demonstration of microscopic preparations of muscle tissue and of the clectric organ of the thormbuck ·Chemistry of Heart Failure 73 treated with potassium reagent of Vaccallum Nederl tijdschr geneesk 65 779 1921 24 Bureau V The repartition of potassium in the cells and the dis placements it undergoes in the course of excitation phenomena Arch internal physiol 39 311 1934 20 Scott G H Distribution of mineral ash in striated muscle cells Proc Soc Exper Biol Aled 29 319 1932 26 Carey E J and Zeit Vicroincineration of active smooth transitional and skeletal muscles Proc Soc Exper Biol - Med 11 31 1939 27 Ringer S and Burton DW Upon the similarity and dissimi larity of the behaviour of cardiac and skeletal muscle when brought into relation with solutions containing sodium calcium and potassium salts Physiol 8 288 1886 28 Starlıng EH Principles of Human Physiology Philadelplua Lea and Febiger 1926 29 Weidmann S Electrophysiology of the Heart Muscle Fiber Pern Huber 1996 30 Cranefield PF and Hoffman BF Electrophysiology of single cardiac cells Physiol Ret 38 41 1938 31 Hecht HH Vormal and abnormal transmembrane potentials of the spontaneously beating heart Ann Neu Jork dead Sc 65 700 1957 32 Prooks C McC Holman BF Suckling EE and Orias o Excitability of the Heart New York Grune and Stratton 1995 33 Huxley AF and Stampflı R The effect of potassium and sodium on resting and action potentials of single myelinated nerve fibers J Physiol 112 196 1951 34 Gelfan S Muscle Ann Rev Physiol 20 67 1998 - 35 Hill A V The abrupt transition from rest to activity in muscle Proc Roy Soc London s B 136 399 1949 36 Tregs 0 W Observations on the structure of striated muscle fibre Proc Roy Soc London SB 116 38 1931 37 Huxley AF and Taylor RE Function of Krauses membrane Nature 176 1068 1935 38 Huxley AF and Taylor R E Activation of a single sarcomere J Physiol 130 49P 1995 39 Heilbrunn L V and Wiercinski F J The action of various cations on muscle protoplasm J Cell + Comp Physiol 29 15 1917 ·74 Chemistry of Heart Tailure 40 Retzius G Biologische Untersuchungen Stockholm Lauder 1881 41 Porter AR ind Palade G E Studies on thc endoplasmic reticulum ll Its form in distribution in striated muscle culs | Biophys Brochem Cytol 3 269 1937 42 Moore DH and Rusk? H Electron microscope study of mani malian cerdi ic muscle cells Brophys Brochem (lol 3 261 1957 43 Vur AR An electron microscope study of the embryology of the intercalated disc in the heart of the rabbit / Biophys 10 chem Cyiol 3 193 1957 ·Chapter VI CHEMISTRY OF THE FAILING HEART Optimum ptimum cardic work can be performed only when the chemical reactions responsible for the release transformation and utilization of metabolic free energy proceed at adequate rates Interruption of the normal sequence of events at any point may result in cardiac failure Therefore from the point of view of energetics the problem of where the defect underlying a given type of failure is located in the energy cycle reduces itself to the following question does the defect concern the release of metabo lıc free energy or does it concern the utilization of metabolic free energy? In the preceding chapters we have developed the thesis that in final analysis energy metabolism in the heart revolves around the synthesis and utilization of ATP and like substances There fore the problem of the cause of heart failure can be re asked in a somen hat different fashion is the failure a result of impairment of the generation or of the utilization of free energy of these energy rich phosphate compounds? Much of the information to be discussed on these and other features of the metabolism of the failing heart can be found in several excellent reviews 16 We shall limit our discussion to those findings which have a firm experimental foundation Much research in this field is either irrelevant fraught with technical problems or carried out under conditions in which its validity at the phy lological level 15 certainly questionable Disturbances in Free Energy Release It is only in failures resulting from disturbances in free energy release that a metabolic defect has been reasonably clearly established Included in this category are failures resulting from anoxia (either due to oxygen 75 ·76 Chemistry of Heart failure lack or metabolic inhibition) coenzyme lack and hormonal imbalance (1) Anoxia Both acute and chronic inoxia lead to heart failure These failures are usually characterized by relatnely lugh cardiac outputs with lost mechanical efficiencies Many of the oxidative enzymes associited with the Kreb s citric acid cycle and the electron transport system deteriorate rather rapidly following periods of relative anoxia? These changes are usually associated nith fragmentation skelling ind distortion of the normal ultra structure of the myocardial sarcosomes & o A number of studies have shonn that the decline in work capacity associated with anoxia is roughly proportional to the decline of phosphocreatine content and later to a fall in ATP concentration 10: Upon rendmission of oxygen both the work capacity and content of energy rich phosphate compounds return to normal Furthermore failures resulting from metabolic inhibi tion (cyanide 2 4 dinitrophenol) are also characterized by a fall of phosphocreatine and later by a decline of ATP 13 (2) Coenzyme Lach and Hormonal Imbalance Probably the most important example of myocardial failure resulting from coenzyme lack is that seen in the disease beriberi resulting from inadequate amounts of thiamine in the diet 16 The heart and other tissues undergo a depletion of cocarboxylase one of the coen zymes concerned with the conversion of pyruvate to acetyl coen zyme A" In this condition the oxidation of carbohydrates cannot proceed to completion As would be expected in thiamine deficiency the myocardia} extraction of pyrunate and lactate is depressed 16 Lactate extraction is apparently inhibited more than pyruvate probably as a result of the adverse effects of clevated pyri ate lcsels on lactic acid dehydrogenase Glucose extraction is also reported to be abnor mally lon Another type of failure of considerable academic and clinical interest is that resulting from thyrotoxicosis The inechanism of the metabolic derangement in thyrotoxic heart disense is not known The arzılıble evidence points to ? defect in frec energy release Oxygen consumption of the heart is usually clei ned last ·Chemisty of Heart Carlure 77 pyruvate and energy utilization is not improved and the overall efficiency is lou 17 The threshold for glucose extraction by the intact thyrotoxic heart is elevated and the extraction coefficients for lactate are reduced Observations on fatty acid metabolism suggest that the heart in thyrotoxicosis depends to a great extent on the uilization of these substances for energy production Myocardial ATP and phosphiocreatine are also exhausted in thyrotoxicosis 18 • The decrease in ATP is probably related to thyroxine s effect on oxidative phosphorylation 1 As with cardiac failure induced by anoxia that resulting from thiamine deficiency and thyrotoxicosis are relatively resistant to the action of the cardiac glycosides Disturbances in Free Energy Utilization There is consider able evidence that congestive heart failure may occur even in the presence of normal free energy release Classical congestive heart failure may be thought of as resulting from a defect in free energy utilization It is characterized by a low cardiac output despite a normal or increased oxygen consumption and substrate utilization and normal contents of phosphocreatine and ATP 3 Such a situa tion is found in failures resulting from chronic valvular and hyper tensive heart disease in man spontaneous failures in the heart lung preparation and failures induced by ion excess and certain nar cotics (nembutal ethyl urethane etc ) 3 They all respond to the digitalis glycosides The basic defect in congestive heart failure appears to be an inability of the myofibril to assimilate phosphate bond energy Whether this is a result of abnormal physico chemical properties of the contractile protein actomyosin or to the loss of essential electrolytes or metabolites has not been clearly established The failure to demonstrate a defect in free energy release in these failures served as stimulus for the search for causes at the molecular level of the contractile apparatus During the past decade a number of reports have appeared dealing with the extractability and physico-chemical properties of actomyosin obtained from hearts in congestive farlure Kovats was the first to develop methods for the extraction of myosin and retomyosin from the heart The techniques have ·78 Chemistry of Heart failure been refined by Benson et al ' ' und later by Deitli and Bing Benson et al report that in dogs with chronic heart failure second ary to surgically produced valvular disease the concentration of actomyosin is decreased These changes were found in both ventri cles despite the fact that the increased nork load 11 7$ usually limited to the left ventricle A decreised viscosity per unit of actoinyosini as well as a reduced response of the viscosity of actomyosin solutions to 4TP was also reported they felt that these changes resulted from actomyosin existing in a partially lissociated state which could be the result of excessive stretching of the myocardul fibers Somen hat similar findings have been reported by Detthi and Bing and Olson et al More recently Ellenbogen et al report further studies on the physicochemical characteristics of myosin Cardiac miyosin iso lated fron dogs in congestive failure 1 75 found to have a molecular height three times (740 000) that of normal hearts (223 000) and the longitudinal dimension of the pirticles was approximately twice that of norinal myosin (1200 Å compared to 680 A1 Apprrently during the desclopment of failure myosin molecules aggregate to form large molecular complexes These authors also interpret their findings as resulting from chronic stretch of the myocarduum which leads to irreversible changes in the size and shape of cardiac myosin More will be sud of these changes later Electrolyte Metabolism The possible relationship of electro lyte discurbances to the mechanism of heart fulure has engendered extensive discussion and prolific writing in recent years For some cime it has been known that conges in the clectrolyte composition of cells may occur in congestive heart fulure. They usually consist of an increase in cell sodium and a decrease in cell potas shim The question immcdutely arises as to whether the observed changes in the heart are of any 6,355C importance in the genesis of the failure or do they merely reflect the response of the heart to an abnormal volume and distribution of fluids and electrolytes 3 The situation is furtier coinplıcated in most clinical condi tuns since çlıgitalis usually has previously been administered in patients with myocardial fyılure Astie shall slios later the glyco sules cause a relerse of the gain of Aa in the heart Honcier ·Chemistry of Heart failure 79 the elaborate and careful studies of Clarke und Moscherzi clearly shon that an almormal distribution of electrolytes occurs in hearts of patients who inve received no glycoside therapy In light of the Anonin role of clectrolytes in inyocardial con traction it is conceivable that a defcrt in electrolyte metabolism may be a causatnic factor in congestie heart failure Honeser the wailable evidence to date suggests that the abnormil Na and k metabolism in this condition is secondary and does not plav a primary role in the genesis of fulure I demonstrable defect in calcium metabolism would be far more significant as this ion is absolutely essential for the process of contraction It is indeed significant that hapeller and hutschera Aichenbergen: demonstrated a diminished crktar con tent in hearts in congestne blure resulting from chronic valvular disease Part of the Ca was bound to the lipoid fraction The decreased ca content of the msufficsent heart was frequently most pronounced on the side bearin., lie greatest fractional load With the development of more refined techniques for estimating bivalen Cations these findings merit further study Jypertrophy Morphologscal Consulerations Probably the most important compensatory mechanism insolved in heart failure is that of hypertrophy The failed heart may increase its mass by as much as six times and its effective work by is much as twenty times 33 Harrison34 1175 postulated that a decise factor in the devel opment of congestive heart failure is anoxia of the myocardium resulting from compensatory hypertrophy He reports that the truckness of the hypertrophied fibers does not permit adequate oxygen chiffusion Weirn' reports that the total capillary CTOS sectional area per unit volume of hypertropluc lieart muscle is v as large as that in normal heirt muscle On the other hand Doch points out that the coronary flou in cardiac hypertrophy without coronary disease is more than adequate to provide oxygen in excess of the requirements of even the thickest fibers Bing et al 37 report that in patients isith con,estne heart failure tesulting from valtu lar discase oxygen consumption is either normal or slighulv elevated The most distincte morphologual feature of lrypertrophy is the increase in the diameter of the individual myocardul fiber with ·80 Chemistry of Heart Tailure little or no increase in capillary supply 33 Linzbach3 lirs shown that in mild hypertrophy there is probably no increase in the num ber of fibers This physiologic hypertrophy is usually seen in hearts weighing up to 500 grams Honever both Linzbuch and Lone and Bare34 pointed out that when this seiglie is exceeded the tluchened fibers split longitudinally producing a net increrse in the number of fibers Apparently with further hypertrophy the daughter fibers also increase in size and split after reaching ? critical width Recent electron microscopic studies have reverled some inter esting ultrastructural correlates to the changes described above Molbert and lijımıobserved that with increasing hypertrophy the myofilaments enlarged and became thicier At a critical size they split into daughter filaments These investigators also described changes in the surcosomes such as swelling diminution of the cristae and shrinking of the inner of the outer to surcosomal mem branes Further details on the endoplasmic reticulum 7 lines and intercalated discs have been described by Bryant er al" Hypertrophy Chemical Considerations It should le pointed out that many of the studies restened in the present chapter on energy metabolism in the failing heart flere carried out ou hyper trophuc hearts There have been only 1 limited number of stuches emphzsızıng the changes in the chemical composition accomping ing hypertrophy Schulze and Sudhofia report an increase in the phospholip & fraction and a decrease in glycogen Sobel and Cohen*l analyzed for a number of protein fractions in the hypertrophic rut hent Increases occurred in all fructions analyzed birt in a dispropor tionate manner The largest increises were observed in the myo globin actomyosin and mitochondrul frictions The authors sus gested that these changes represented an adaptation to the increased demands placed on the heart The increase actomyosin content may explain the obseried increase in ATPase activity reported by Rossi und Drinzını Vor* The latter appeared to be related to szrcosomal dimage hoseier oxidite phosphorylation as not changed during the period of obseration The same authors also report that an initial increase ·Chemisti) of Heart Failure 81 in ribonucleic acid occurred m the tissue homogenates and isolated mitochondria this returned to normal in four months The desoxyribonucleic acid per unit weight was not modified after observation for eight months but the total amount increased due to the increased number of nuclei Nowy et al* report only a slight increase in ribonucleic acid a slight decrease in desoxy ribonucleic acid and no changes in total phosphate or inorganic phosphate in rabbit hearts after six months of hypertrophy These findings suggest that an increase in protein synthesis occurs during the initial stage of hypertrophy as one would expect It is of interest to note that cardiac hypertrophy does not occur in hypophysectomized rats • Treatment of such rats with growth hormone restores the ability of the heart to undergo hypertrophy REFERENCES 1 Cruikshank EW H Cardiac mctabolism Physiol Rer 16 97 1986 2 Evans CL 'The metabolisin of cardiac muscle Recent drances in Physiology 6th edit Philadelphia Blakiston 1939 3 Wollenberger A The energy metabolism of the failing heart and the metabolic action of cardiac glycosides I Pharmacol Le per Therap 97 311 1919 1 Olson RE and Schwartz W BA[yocardial metabolism in con gestive heart failure Medicine 30 21 1951 5 Bing RJ The metabolism of the heart The Harvey Lectures 1954 5 New York Academic Press 1956 6 Gertler MM Consult ed Metabolic factors in cardiac contrac tility Ann New Fork Acad Sc 72 387 1959 7 Michal G Buren A Hogencamp CE and Bing RJ Effect of interruption of coronary circulation on metabolism of the arrested heart Am J Pliysiol 195 417 1928 8 Molbert E and Iijimas Beitrag zur experimentellen Hyper troplue und Insuffizienz des Hermuskels im electronenmikro skopischen Bild Naturwiss +5 322 1998 9 Bryant RE Thomas W A and O Veal RM An electron microscopic study of myocardial ischemia in the rat Cire Re search 6 699 1998 ·82 Chemisin of Heart Failure 10 Chang I Effect of asplıyari on the adenosinetriphosphate con tent of the rabbit s heart Quart | Leper I lysiol 29 3 1938 11 Clark A ) Eggleton MG und Eggleton P Phosphi,en in the perfused heart of the frog | Physiol 75 322 1932 2. Veicher B Uber den Chemismus des tatigen Herzmuskels Arch exp Pathol u Pharmakol 174 383 1931 13 Wollenberger I and harsh L Łffect of 2 cardic glyclosule (ou ibain) on the contraction and the energy rich phosphate con tent of the herri poisoncu path 2 1 dinitrophenol / Pharmacol - Exper Thesap 105 477 1932 Btu vell CS and Dexter L Berubcri heart disease try on Plisecrans 60 59 19 17 15 Oclioa and Peters R A Vitamin B3, ind cocarboxylase in inimal tissues Biochein 32 1501 1938 16 Hackel E B Goodale II 1 and kleinermin | Effect of the minc deficiency on myocadil metabolisın in intact doo Am Heart) 46 883 1993 17 Olson RE and Piatnck D 4 Conservation of energy in curdic muscle din lew l ork 4ond Sc 72 166 1999 18 Berg H Uber den Herzmuskeistoffwechsel bes Hyperthyreose und seine Reeinflussung durch Vorimin C sich eeper Pathol n Pharmakol 185 359 1987 19 Waltonet C Chemischer Beitrag zur Frage der Herzmuskel schadigung durch Iliyroun Etschr ges exper Med 90 237 1933 20 Schumann H Experimentelle Befunde nur Frist festo LEIKS Thyroxinemptindlichkeit des nicchisch vermehrt belasteten Herzmuskels Zischr ges exper Afed 105 577 1939 21 Lehninger IL Physiology of mitochondr2 relonslupes be tuccn mitochondrial structure oxid the phosphorylation end action of thyroxine Internal Symposium on Inymes 1955 (publ 1930) 22 hoiats ] Myosin and actomyosin content of the heirt musck Vature 163 606 1919 23 Benson ES Hallway B E and Frog Er Extraction and quantitative characteristics of actomyosin in cinine heart mus cle Circ Research 3 215 1995 24 Benson ES Composition and state of protein in die ist mu clo of normal dogs and dogs with experimental myocardial iuture Circ Research 1 221 1995 ·Chemistry of Heart Failure 83 23 Deuth L and Bing RJ Contractility and extracubility of heart actomyosin after death Cure Research + 519 1956 26 Olson R L Ellenbogen Ł Stern H and Liang VVL in abnormality of cardiac myosin associated sith chronic congestive heart failure in the do, J Clin Inu estigation 35 727 1956 ?, Flenbo,en I langar Rind Olson R E I roperties of myo sin from normal and fulin, dog hearts rederation Proc 18 221 1959 Calhoun J | Cullen Gk Claric G und Hurrison TR Stuclics in congestive licurt fulure VI I he effect of overwork and other factors on the potassium content of the cardic muscle J Clin Im estigation 9 393 1930 99 Iseri L1 Alexander I 6 VcCauglicy RS Boyle Jind Vyers CB litter and clectrolyte content of cardiac and skeletal muscle in licart failure and myocardial infarction ton Heart J 13 215 1952 30 Danowski IS Elcctrolytes and congestive heart failure dun Internal Med 37 153 1933 31 Clarke E und Voscher RE The water and electrolyte con tent of the human heart in congestive heart (tlure with and without digitaluation Circulation 5 907 1932 32 hapeller R and hutschcra lichenbergen H Uber den Calcium gelialt des Herzmuskels Brochem Ztschr 193 100 1928 33 Grint RP Ispots of cardiac hypertrophy im Heart / 46 151 1929 31 Harrison 1 R I alwe of the Circulati un 2nd edit Baltimore Tilliams and Wilhins 1939 32 leirn 1 Morphological ind functional alterations of the coronary circulation Bull Ten Torl Acad M 17 751 1911 36 Doch W (apacity of coronary bed cudiac hypertrophy I rx per Med 74 177 1911 37 Bing R) Hammond IV Handelsm in Iclouers SR Spencer F C Eckenhoff J ! Doodale 11 T Hafkelschiel JH and hcty s The measurement of coronary blood flow oxygen consumption and efficiency of the left ventricle in min Am Heart | 391 1919 38 Linzbuch Vikrometrische und lustologische Analyse lyper tropher menschlicher Herren fich pathol Anat Plyysiol 314 584 1916 ·841 Chemistry of Heart failure 39 Lowe 1 E and Bate E W Hyperplasia of cardıc niuscle fibres MJ dustralia, 1 618 1948 40 Schule G and Sudhof H Uber den Lipoidgehalt des lypertro pluerten Saugetierherzens Arch ges Physiol 358 211 1933 Sobel Hand Cohen F Proteins of heart and experimental car diac hypertrophy in the rat Proc Soc Exper Biol & Med 99 656 1958 12 Rossi G F and Diatani Mor MA Oxidative pliosphorylation and adenosinetriphospliatase in the sarcosomes in experimental hypertrophy of the heart Sperimentale 108 378 19,8 13 Rossi GF and Dianzanı Nor V4 Vucleic acids in experi mental hypertrophy of the heart Sperimentale 108 389 1958 11 Nowy H Frings HD and Rey h. On the nucleic acid content of normal and lıypertrophicd rabbit hearts Ieperientin 15,0 1999 15 Beznak M Effect of growth hormone preparations on cardiac hypertrophy and blood pressure of hypophysectomtzed rats am J Pliy stol 184 563 1996 ·Chapter VII ACTIONS OF DIGITALIS Witherings was the forst to recognize that digitalss had pro found effects on the mohons of the heart He actually developed successful methods for the urse of this agent in treating dropsy disease syndrome which we recognize toclay as congestive heart failure In 1882 Schmiedeberg determined the basic actions ol the digitalis substances and began a study of the action of purified glycosides Frrenkel introduced stroplantın m glycosidle therapy of heart disease in 1905 after preliminary animal experimentation* The rapid progress made in mascle chemistry and energetics of muscle contraction durmg the period 1910 to 1950 served as a stimulus for search for the mode of action of these agents at the chemical level During rf25 zmierzal a besuulderin, number of studies have appeared Interest is continuing at an accelerated raic From a chemical and pharmacological point of view the most important site of action of the castlac glycosides is unquestionably the myocardium The systolic force of muscle contraction of the failed or hypodynamic heart is increased In fact all the effects on the heart can be explained by an action on this parameter Idlmit tedly these agents have effects on cardiac reflexest and renal excre tion of electrolytes Honever the magnitude of the changes incluced are not sufficient to account for the therapeutic effectne ness of the drug in the preceding chapter we noted that failures resulting froin a defect in free energy release do not respond effectnely and efficiently to digitales Benefull effects of the drug were only obtained in failures resulting from disturbances in free energy italization These findings indicate that digitalis is active by virtue of its ability to improve the utilization of metabolic free energy 82 ·86 Chemistry of Heart Palme In the present chapter we shall brefly relies some of the pertinent evidence which substantiates the above hypothesis Overall Metabolism One of the most distinctive and easily reproducible effects of digitalis on overall metabolisın is its action on oxygen consumption of myocrrdial tissue In 1912 kohde und Ogals reported that strophanthin depressed consumption of the frog leurt In 1930 Eismayer and Quinche obtuned consider able mereises in Ouptihe mith 1 very low concentration of strophanthin which had no influence on the work output of the heart in the same year Daud noted that strophanthin caused 1 similar increase in respiration of frog atrı wuch n as later folloned by a decline to belon normal levels Since the frequency of bent was lowered and the amplitude of beat not greatly augmented this stimulation of oxygen consumption seemed to be a primary effect This effect on ouygen consumption has been observed on nuinerous occasions in steadily respırıng cardıc tissile sticesI The effect is observed at low pharmacologically active concentra tions Increises of ovygen consumption are usually observed in trilly (30 mutes to l hodir) folloncd later by a profound de pres This effect is blocked by increasing the h conceiurition "3 but occurs in the absence of Ca ! Significant changes in the respi ritory quotient have not been notcai "' In higher love concentra cions the glycosides increíse the O consumption of brain slices sa Tlie intact cardic muscle fiber is required for the abrua effect In concentrations 100 times those exertig in effect on cardiac tissue slices ouabuin has no effect on fortified or uintorufied horno genute respiration " Turthermore the drug has no effect on the respiration of normal mitochondrız or those whose respcion Inas been depressed with metabolic inhibitors' 16 This effect on respiration has not been universally nutpical For example Bing und associates have found that strophithin did not modify coronary blood floss or nerobic meraboly } either normal subjects or patients riith cardiac insufficiente It the present time there is no satisfactory explanahon fir this »CTEISC 2nd subscquent decrease in the rate of respiration Increased cell permeability 1* 19 either to exogenolis essential sul sion ·Chemistry of Heart Toilure 87 strates or to normal utracellular metabolites has been moled on several occasions Fillestein and Bodanshyl pomied out that the observed increase in ou gen consumption may well result írom the develop ment of a contrarture innat occurs in the presence of the glycosides In fact Victor reported that ourbun in rather high concentra trons greatly increased consumpron and he found reritricular muscle firmly contracted at the end of the experiment This hypothesis could not explain the increased ovsen consumption of brain slices induced by digitalis Recently it lias been shown that ourbain increrses Ca infi It is well knon that Cr is an actuator of ATPase particularly myosin ATI've The Incre ised 1TP1sc activity th 10 might occur under these condicions rould Icad to an accumulation of free PO, and ADP Both of these agents are activators of the glycolysis and oxidatne phosphorylation reactions The elevated oxygen consumption is tell be the result of such a sequence of reactions In Leeping with this fiy porlesis is the finding of a falt of creatine phosphate and later ATP in hearts after prolonged Treatment with ouabain On the other hand this idea u ould trot explain the subsequent decrease in respiration Free Energy Release An almost overwhelming and bewilder ang number of studies on the effects of digitalis on the retabolic patterns insolved in the release of free energy have appeared dur past 30 years Much of the data is conflicting and difficult to analyze Therefore we shall limit our discussion to studies that allustrate the problems involved Gremels reports that digitalis increases glucose utslization at constant work levels in the heart lung preparation Apparently a sharp rise in tactic acid uptake occurred after admunistration of nontoxic doses of ovabain to dog heart lung preparacions Follow ing the administration of digitalis myocardial glycogen content iras been reported to be increased #deutenged ? 8 or not signifu cantly altered 30 Bing and associates report that digitalis has no effect on myocardial exeraction of glucose lactate pyruvate or Letone bodies in the normal and failed heart $1 Averbeck states that cardiac glycosides accelerate the anaero ing the ·88 Chemistry of Heart Failure bic oxidation of glucose hexose diphosphate glycerophosphae and lactate Succinue ovdation was reported to be increased in minced cardiac muscle The cytochrome oxidase system appears to be unaffected by digitalis 103 Neither does the presence of cardırc glycosides late any influence on the electron trinsport system 19 nor on the effi ciency of oxidative phosphorylation 3 Theripeutic concentrations of these agents have no effect on the ATP and phosphocreatine content of the normal or failing heart · Higher toxic doses ciuse z rapid depletion of the energy rich phosphate stores 33+ This fall in enersy rich scores has been interpreted by some as resulting from in inhibition of ITP syn thesis relative to ATP breakdown However it was pointed out above that these agents have no demonstrable effects on oxidame phosphorylation It is highly probable that the loss of energy rich stores may be the consequence of an increase in the rate of breakdown of 4TP It is concentable that the actity of the Cactrizred myosin 4 TPase of heart might be increased by the glycosides perhaps through mobilization of calcium is pointed out earlier Free Energy Uulizaron There is considerable endence 11 uu] able which suggests that digitalis has effects on the physico-chemical properties of the ATP actomyosin system in 1949 Mallor and Robbs showed that the shortening of accomyosin threads induced by ATP was increased by digitalis This finding has been con firmed by Bonien 36 Horth et al " reported that the rate of poly merization of actin 17s enhanced by small amounts of digitovat Similar obserı 101ons lere made by Wollenberger 3who compared the effects of 1 number of active and incre glycosules Houcier he concluded that there was no correlation between the in uso action and the effect on isolated protein Waser391 found that pharmacologically actile glycosides decreasedi the thixotropy of actomyosin and increased the k binding capacity of this protem Inactie glycosides had no effect Waser and Volkarers reported that several glycosides reduced the viscosity of atomyosin solutions but not of myosin n did not affect the degradation of ATP by myosin solutions Detti and ·Chemistry oj Heart Failure 89 Bing i found that actomyosin bands prepared from heres i con gestie future shoned reduced contractility when compared to those prepired from normal hearts Both preparations were unaf fected by digoxın or by Ci alone However in the presence of digoxin plus (a (10 'V) the contriculity of the protein isolated from hearts in congestive frilure returned to normal The glyco side had no effect on the glycerol extracted heart fibers It should be pointed out that the latter preparations have no functional membranes anul tre electrically inexcutable Electrolyte Metabolism It luus long been knoun that the systolic action of digitalis » influenced by the ionit enuronment The NaCl content of the suspendmg medium docs not seem to affect the rettun directly for s may be reduced considerably with out changing the action of digitalis providing the osniouc pressure is maintained ith sucrose It is of interest to note that Daly and Clark observed that the cffects of decreased 17 showed remark able similarity to those of stroplianthin An increase of k lessens hule a decrease enhances the systolt action of digualis Appar ently in increase in pH frors the actions of strophanthin Special interest is attached to the relation of calunum to diga talis action It has long been known that ca increases the force of contraction and promotes the deselopment of contracture in a manner similar to digitalis Furthermore calened contractions of hearts bearing in La deficient media can be restored to normal by the addition of strophanthin When the calcium is reduced nearly to zero the systolic action is greatly impured In 1919 Konschegge rorking in I oems laboratory sugessed that strophanthin could substitute for Ca loent developed the thesis further and pointed out that the glycosides may activate the Cu of the heart or sensitive che muscle to the Ca si contains These obsersations suggest that digitalis might have actions on electrolyte metabolism Honeer it was not until the studies of Calhoun et al 4' that concerrell eftotts niere made to determine whether digitalis Ind demonstrable effects on electrolyte metabo lism in the heart Tlie finding that liearts of patients dying of congestie fulure were normally Jou in h content lead them to suspect the digitalis might have effects on h metabolism in the ·90 Chemistry of Heart Failure heart In ? well controlled series of experiments on dogs theobserved that toxic and frtal doses of digitalis markedly diminished the h concentration in the heart but not in skeletal muscle 50 Since these original observations a large number of piper have appeared which show that digitalis in therapeutic or toxic doses decreases myocardial Ki The loss of his accompanied by a corresponding increase of cell Na Wood and Moe showed a positive correl ruion between the increased mechanical efficiency and rate of loss of myocardial k This thesis has been expanded into a rather elaboruc theory by Hajdu to explain the mode of action of digitalis Recent studies on erythrocytes58 and cardiac muscle indicate that the loss of h and gain of Na result from an inhibition of active Na efflux and k influx Solomon et al B suggest that digitalis com petes in a reversible minner with Na and k for the active transport carriers Glynn & reports that digitalis also blocks passie trans port of Na and k while Holland and hleines present data suggest ing that digitalis under certain conditions increases passive memi brane permeability to these cations Recently Holland and Schui have shown that digitalis increases Cl influx The chemical mechanism ini olied in the action of cardin glycosides on active transport is at the moment incompletely under stood As pointed out in in eirlier chapter there is evidence that a membrane ATPase is part of the actie transport cotrier system Recently Posto observed that in hemoglobin free erythrocyte niem branes ATPase activity was approximately doubled by the delicion of both Na and k together but not by either ion separately The increase in activity was prevented by ouabain (10-7-1) Earlıer Holland Greig and Dunn" observed a similar coinpe tition between hand onabain in the acetylcholine cholinesterase system The concentration of ouabain used was higher by a factor of ten than that employed in the above studies in an earlier chap ter ut nas postulated that the two enzymes might be part of a large molecular complex in the cell membrane controlling active and passite movement of Na and h Therefore it is possible that the glycosides produce their effects on active and passive movement of cations by interaction with this molecular system ·Chemisty of Ileart Failure 91 Interest in C1 and its possible relation to the mode of action of digitalis has been recently revicd Wilbrandt and Caviezel43 have described experiments which appear to show that digitalis prevents the loss of myocardial C1 probably by depressing Ca out flow Lrter Tliomis et al 1 and Holland and Schul showed that ourbain had no demonstrable effect on Ci efflux but murhedly increased Ca influx The latter authors showed that this cffcct was enhanced by an increase of C1 ind blocked by an incrcise of k in Ringer s solution Niedergere presents evidence that much of the enlcium involved in contraction is very rapidly exchangeable and probably involves that in the membrane The fast exchangin, fraction repre sents only a small portion of the total (1 to 2%)* The more slowly exchanging calosum (bound form) is not involved in rapid changes in contractility It is possible that digitalis affects only the rapidly exchanging component This might explain why some investi gators report systolic effects of cardiac glycosides in media which were thought to be free of calcium Ilalu and Leonardo suggest that the increased Cr influx may result from the great loss of a that occurs in the presence of digitalis The cardiac glycosides also have effects on the electrical prop erties of the leart an action probably resulting from an effect on membrane permeability Initially these agents lengthen the dura tion of the transmembrine action potential by increasing the platcau Later a shortening and spiling of the potential is observed This is followed by a loss of overshoot an increase in membrane resistance and after long cxposure a decrease of mem brane resistance 67 68 RETRENCES 1 Wathering W An account of the forblose and some of its med cinal uses with practical remarks on dropsy and other discases London Robinson 1785 Reprinted in Medical Cinssies 1937 2 Schmelcberg O Beitrage zur Kenntniss der Phyrmakologischen Gruppe des Digitalıns dirch exper Pathol u Pharmałol 16 149 1882 3 Fraenkel A Vergleichende untersuchungen uber die kumulauve ·92 Chemistry of Heart Failure Wirkung der Dı,italsskorper dich erper Pathol u Pharmal ol 51 84 1904 4 Heymans C Bauchaert J and Régniers P Sur le mecum rellere de la bradycardie prosoquee par les digitalıques Compi rend soc bol 110 572 1932 5 Furber S J Alexander J D I ellegrino E D ind tirle D P The effect of intravenously adnunistered di,oxin on water and clectrolyte excretion and on renal functions Circulation + 3,8 1951 6 Rolle Eind Oka 5 Gasti echsel und Tatigkeit des Herzens unter dem Einflus von Giften und erscnreizun, toch exper Pathol 1 Pharmal ol 69 200 1912 7 Eismuver Cand Quinche H Stoff echseluntersuchungen am haltblutlerlierzen ili Mittclun, Sauerstoffverbruch hohlen saure und Milchsaure 4bgabe des Herzens bei verschiedener Arbeit Zische Biol 99 529 1930 8 David C The action of drugs on the oxygen consumption of the frogs isolated surcle | Pharmacol roper Therap vo 229 1930 I Lev and Liberto Pharmacodynamic cellulare Ul Etude due mode d action des cligutuliques Respiration des ccllules du myocarde sous l influence des scillencs 4 et b Bull Sor chim biol 29 269 1947 IO Wollenberger Metabolic action of the cardiac glycoses I Influence on respiration of heart muscle and cortex / Pharma col Frper Therap 91 39 1917 !! Tinklestein M and bodansky o The effect of cardic glycosides on the respiration of cudiac muscle Pharmacol é teper Therap 94 274 1918 12 Dubois A P Doull 1 and Cerling I. vh Infubitors action of bufa,in on carbohydrate oxidation Federation Proc $.297 1919 13 Dunn GL Holland !! Cand Creig I Possible ruition shup beaucon acuon of digitalis on oxygen consumption and acetyl choline turnover Tederation Proc 133,0 1901 14 Hermann RC Studies on the cffcct of ourdun on curdic mis cle respiration Arch internal pharmacodyn 31 23, 19,8 15 Lancmann H Brody IV and Bain J A Oubun an slices and mitochondrial preparations from ik in! and brain / Pharmacol! Hyper Therap 108 274 1933 In vitro effects of ·Chemustry of Heart ( arlure 16 Holland WC und Dunn (I Role of the all meinbrinc und imitochondri in the phenomenon of lan trusport in careliac muscle im J Physiol 179 186 1991 17 Bing RI Haigimond VV Handelsman 1 Powers SK Spencer IC Ichenhoff I Coulik i Hofhensche? I land cry The Mastercient of coronary blood flow olen consumption und efficacy of the left ventricle in man 11 Herst) 393 3984 18 Lenale L Distaliskurper und kurwandte herzuerkrime Chla sidic (Diosiloide) In Hefflers Handbuch der erperimentellen Pharmakologie Erg anrungsuerk Berlin Springer 1033 19 cosc H Digitals Leipzs theme 1996 20 Victor 3 The effect of ouabun on the oxygen consumption of cardiac vcntricular muscle troc Soc l'eper Broldled 30 899 1992 21 Thomas L. Jolley 1 und Grechmi R Łllect of calciunt lack and ouabats on calorum uptake sa frogs leirt lederatson Proc 17 16 1998 29 Holland Hand Schul 1A Effect of ouabain osia and C178 exclunc in isolated rabbit aira Am J Playsrol 197 757 1939 3 Wollenberger ! Metabolic action of cardiac glycosides 311 kr fect of oubain and digoxin on the encrgy rich pliosphare con tent of the lart / Pharmacol urxper Cheap 103 125 1991 21 Cromels H Ducr ck Beachungen des Kohlehydratstoffscchsets zur ! hystolove und Pharmakologs der Herreteryctik Arch erper kathol « Pharmakol 194 629 1910 20 D Vessandria Iniluenze di cardiocenetici sul glico, en del musculo cardiaco Tola med 18 3399 3932 26 Cherhes AI Horimirclwirkung uud Herzstoffwechsel Acta Med LSIR 3 19 1910 27 Homskoy and haullut hy Ubu die trkung von Sterin dcrkativen auf den Stoffwechsel Ober die Wirkung der Digitalissubstansen auf Leber Herr and Muskelglykogen arch exper Pathol u Pharmakol 198 22 1911 Untersuchungen har den hohlchydratssofficchsel de Hurren 31 Experimentele Untersuchungen Der Eufluss der Digitalisimuppe auf den Kohlhydratgehalt des Herzen Arch exper Pathol u Pł arm rol 196 197 1910 28 Liebig H ·94 Chemistry of Heart Failure 29 himura TE Effect of cardiac drugs on the phosphorylated intermediates of the rat Proc Soc Erper Biol & Ved 69 419 1948 30 Yorimitsu T Uber den Einfluss verschiedener Herzmittel auf den Kohlehydritstoffucchsci des Herzens Jap Nied Sc 11 13 21 1910 1 31 Bing R) Disturbances in myocardial metrbolism Fortschr Anidiol 1 52 1956 32 Averbeck B Uber den Emfluss von Strophanthin auf die Afethyl enblaucnttarbung Inaugural dissertation Universitat Vatnster 1932 33 Grisolia S and Ito discussion of the site of action of digitalts In Durtalis od bs G Dimond Springfield II! Thomas 1957 34 Weicher B Stoffwechselwirkung des Strophanthin am Warm blutlerherzen Arch erper Pathol u Pharmałol 1,8 521 1955 35 Malloy Sand Robb J S Behavor of actomiosin threads rederation Pro 8 101 1919 30 Bonen 1 J Effect of digoxin upon rate of shortenin. of myosin B threads Federation Proc 11 16 1992 37 Horath I heraly C und Szerb I Iction of carduc glicosulcs on the polymerization of actin Nature 164 792 1919 38 Wollenberger A Non specificity of the effect of erec glucosides on the polymerization of actin repenentia 10 311 191 39 Waser PG Bindung von Heroglyhoshen an Actomyosin flel vet phasol et pharmacol acta 13 C37 1939 40 Waser PG Uber die Wirkung von llcrzgly hosiden auf Ictomyosin Cardiologia 29 214 1956 Wiser P G Olynt die 11 thung von Herzglykosiden af Ictomyo 3 Thuothropieser inderungen fehet physiol et phar macol acta 15 123 1907 12 Waser PG Versterke Bandung Ton halumionen 711 Iconos durch herzwirksame Glykoside Heliet physiol et pharmacol afta 15 CH2 1997 43 Waser P Gin Volhart Wirkung ron Herzlyhosrden aul Actomysin Heltet physiol et pharmacol acta 12 12 1911 11 Detil Land Bing RJ Contractile properhes of actmusisaster creads and bands prepared from dog heitt am I insol 197 145 1996 sin ·Chemistry of Heart Failure 1Szent Gyorgy | Chemısın of Vuscular Contraction and edit ew York Aademic Press 1951 46 Daly I de B and Clark a J 1 he action of ions upon the frog heart J Physiol 54 367 1921 47 Konschegg A von Uber Beziehangen zwischen Herzmittelund physiologischer hationenwirkung Arch exper Pathol u Phar makol 188 226 1938 48 Loew. O Über den Zusammenhang zwischen Digitalis-und hal ziumwirkung Arch exper Pathol u Pharmakol 82 131 1917 49 Calhoun J A Cullen G C Clarke G and Harrison TR Studies in congestive heart failure VI The effect of overwork and other factors on the potassium content of the cardiac muscle J Clin Investigation 9 393 1930 50 Calhoun J A and Harrison T R Studies on congestive hcart failure IX The effect of digitalis on the potassium content of the cardiac muscle of dogs Chin Investigation 10 139 1931 51 Loyer P and Poindexter CA The influence of digitalis on the electrolyte and water balance of heart muscle im Heart , 20 586 1910 52 Hagen PS The effects of digilanıd C in varying dosage upon the potassium and water content of rabbit heart muscle J Phar macol Exper Therap 67 50 1939 53 Hajdu S Mechanism of staircase and contracture in ventricular muscle Am J Physiol 174 371 1933 51 Holland WC Greig ME and Dunn C E Factors affecting the action of lanatoside C on the potassium content of isolated perfused guinea pig hearts Am J Physiol 176 227 1994 53 Gonuduhol F Siegel A and Bing R J Effect of a cardiac gly coside (cedılanıd) on the sodium and potassium balance of the human heart Circ Research 4 298 1996 56 Gertler M M kream ) Hlylen J W Robinson Hand Nedle EG Effect of digitoxin and quinidine on intracellular electrolytes of the rabbit heart Proc Soc Erper Biol & Aled 92 629 1956 57 Wood EH and Moe GK Correlation between serum potas sium changes in the heart lung preparation and the therapeutic and toxic effects of digitalis glycosides 4m J Physiol 129 199 1910 58 Glynn IN Iction of cardiac glycosides on sodium and potassium movements in human red cells J Physiol 136 148 1937 ·06 Chemistry of Heart failure 59 Rigner B 1nd leatherall A Digoxin quan the parassit moiement in rabbit wricles Brit J Pharmacol 12 371 1931 60 Solomon Ik Cul 1 Cind Gold L I he kinetics of cardiac discoside inlibition of potassium transport in human erythrocytes 1 Gen Physiol 10 327 1926 01 Holland IV C and Klein RL The clicct of acetylcholine oul? bin ind quinidine on the irinsmembrane flux of k in isolued rabbit atrı? Federation Proc 18 103 1919 62 Post R L Relationship of an Al Puse in human erythrocyte membrincs to the active transport of sodium and porassium rederation Proc 19 121 1959 63 Wilbrundt il and Celezel R Dic lccinflussung des lustritts von Culemun rus deni Herzmuskel durch ierigk koss? Heel physiol et pharmacol acta 12 C10 1991 61 Micderscrke R 1 he rate of action of calcium ions of the con triction of the lieart J Physiol 1,5 506 1957 05 Harris I ) Output of calcium f) Irom frog muscle Biochim et Biophys Acta 33 80 19.7 66 Hajdu sind Leonid r I he cellular basis of cırdır glycoside action Pharmacol het 11 173 1939 67 Tloodbury Li and Hecht HH Effects of cardne glycosides upon the electrical ictivity of single ventricular fibers of the frog heart and tlicur relation to the asgitalss effect on the electro cardiogram Circulation 6 172 1952 68 Dudel | ind Trautsein ll Electroplıysiologische Messungen zur Strophanthinuirkung im Herzmuskel doch exper Pathni Pharmakol 272 399 1998 ·Chapter III THE NATURE OR CONGESTIVE HEART FAILURL AND THE MODE OF ACTION OF DIGITALIS The analysis in the preceding clipters revealed that only in those cardmc failures resulting from metabolic mlubition vita min deficiency or hormonal imbalance could a metabolic defect be implicited as the cause of reduced mechanical effociency A dis turbance in free energy release seems reasonably clear Such ful tires do not respond sell to digitalis and only by allevang the precipitating fictor can they be effectively corrected We presented strong evidence that in those failures which respond to digitalis the cause of mechanical inefficiency seemed not to reside in a reduced energy supply but in an inability of the myocardial fiber to transform metabolic free energy into mechan Ical vorh The most important examples in humans are congestive failure resulting from chronic hypertensive and valvular disease and certain experimentally induced fulures in the dog heart lung preparation Only these types will be considered in the present chapter Theories of Congestue Failure Tliere is nou general agree ment that the development of congestive failure results from a dininishing work capacity per unit weight of myocardul tissue ! Apparently when this parameter falls below a critical value symp toms of franh congestie failure appear Probably the oldest and most widely accepted theory to account for the events accompanying the des clopment of congestise heart failure is that due to Frank and Starling 3 These investigators shoned that the contractile energy of the heart was a function of the initial length of the myocardial fiber Contractile force increased in direct proportion to initial fiber length up to a certain critical 97 ·98 Chemistry of Heart Tailure one further lengthening resulted in dımınıshed contractile energy Starling further proposed that congestise failure resulted when the fibers were stretched beyond this critical length due to excessive loads being placed upon the heart Therefore according to the views of Frank and Starling excessile stretch of the myocardium is of prime importance to an understanding of the mechanism of congestive failure The validity of this concept has been recently challenged pir ticularly by hatz* He believes that the initial length of the fiber is not the sole factor governing the release of contracule energy the velocity of contraction and neurohumoral events should also be considered However the carefully controlled studies of Sunoff clearly show that under any given set of hemodynamic conditions a direct proportionality exists betueen contractile energy and diastolic volume Thus the validity of the Frank Starling principle seems to be well established at the present time The importance of the velocity of contraction is a fictor con trolling the release of energy should not be minimized In skeletal muscle it has been shown that the slower the velocity of contraction the greater the rule of energy release & Furthermore skeletal mus cle liberates extrı energy for work? (Fenn effect) Such crucial findings have not been tested on the heart and their role in con trolling the work of the herrt is not clearly er aluated Harrison' postulated that a decisive factor in the desclopment of congescuie farlure was relatne anovi resulting from compensa tory hypertrophy He thought that the thickened myocardial fiber limited the diffusion of oxygen and essential substrates Honcier in Chapter I we presented arguments that invalidate this thesis There is considerable cudence avulable uluch suggests that congestie lieyrt fulure is the result of changes in the pinysico chemical properties of the contractule proteins Thuis is eertuinly in keeping with findings of a diminished actomyosin concentration in filed liearts as well as the isolation of cardic myosins bruing abnormal plıysical properties In addition the contractility is reduced in glscerol extrated fibers prepared from hearis in conges tric failure One of the mujor obstacles to the acceptance of such a theory is that muscle protein chianges were found in borh 1:19T ·09 Chemistry of Heart Failure cles despite the fact that the increased tork lord is either limited to the right or left ventricles Another explanation for the reduced mechanical efficiency is that there is some iteration in the intracellular ionic environ ment which results in a diminished contriculity It was pointed out earlier the hearts of parents dying of congestie failure are lou in h and fugh in Na This finding was complicated by the fact that many of the patients had recensed cardiac glycosides agents Inoun to produce comparable electrolyte distribution However in the studies of Clarke and Voscher10 a similar picture was observed in patients not recening digitalis In fact these juthors believe that digitalis eles ates the low h levels back to normal It is still a controversial matter as to whether the reduced h and elevated M7 is the cause or result of cardiac insufficiency Similar chinges have been reported in sheletal muscle of patients with non-cardiac edemn11 VcDowall et al 1 believe that cardiac failure results from the inability of the heart to extrude Na actively The arcuriulation of M7 has deleterious effects on the contractile apparatus This hypothesis would explain why decreasing the Na content of the inedium increases the contractile strength of heart muscle However Niedergerke and Harris13 have recentlv shown that a decrease of Nn increases the uptate of Ca The role of Ca ions in congestive failure should be considered because of their well known effects on muscle contractility Unfor tunately little or no attention has been given to this problem in recent years This is probably a result of the fact that total tissue calcium is difficult to determine and that calcium exists in several forms in tissue In this connection it should be noted that hapeller and kutschiera Aichenbergen't found a diminished Ca content in hearts in congestive failure resulting from chronic valvular disease The decreased ca as most pronounced on the side bearing the greatest Horh load of the various theories proposed over the past 50 years to explain congestive failure that of Frant and Starling is the most Teasonable and is in keeping with recent studies on muscle contraction Farlier se discussed evidence which indicated that heart and ·100 Chemistry of Heart I ailure sheletal muscle contract to perform work by an interrction between sites on overlapping myofiliments in the sarcomere Ipparently the mierīction is ben een ATPre sites on the dense myosir fila ment the A bind and ITP bound to actin in the thin I bind filament 1 he reaction permits the actin filmeyit to slide post the more ngadly fixed myosin one The energy released in the form of work is determined by the extent of interaction which in turn is controlled by the reare velocity of inotion betucen fil unents and the concentruon of ionized calcium the sloner the relatie motion the greater the interaction Ionized Cr is thought to act exther by strengthening or establishing cross links betri cen the fill ments or by increasing (TPase activity and thereby colizing the probability of interaction If the sliding model is a correct sepresentation of the events 15sociated with normal contraction then contrition should be wcalened or cease when the stroomcre is stretched beyond critical length (about 35 p) This length should be the sum of the lengths of the \(1 5w) and I (204) band filaments Huxley und l'enchey' showed that i muscle fiber with ? stromer length of 15 H shortened greatly on stimulation but if streched to 30) ff it did for shorten it all This is mileed a relatively narrot rin, Fur thermore they pointed out that when an intact mus le fulcr as stretched the surcomeres in the middle of the muscle bundle extend more than those at the ends It should be recalled that Starling felt that congehuile Suure resulted from the myocardul fiber bung stretched beyoud 16 71 length Therefore in light of the sliding inodel it is concenoble that excessive stretch may so displace the myofuiments conc co ench other that interaction is decreased or absent rusulun. 11 dushed contractile strength When a sufficient number of the myofibrils are involved frinh congestive fuure results ricessive stretch my lead to other changes that contribue 10 the severity of fulure for example creessive stretci in ay dasturi the physicochemical strticture of the actomyosin molecut so 157 its ion bindin, cipicity is elistushd und essential electrolytes ir last It is well known that ionized czlcium is a potcnt in or of myosin ATPase activity According in the chuling model ilic ·Chemistry of Heart lailure 101 probability of interaction of the ATI ase site on the tluck myosin filament with bound ATP on the actin filament would rise or fall with an increase or decrease of ATPase activity Thus a decrease of ionized C# in tlie environs of the contractile elements is is reported to occur in congestie fulure would reduce the rate of energy released with each contraction The Mode of Action of Digitalis There is no doubt that digicalıs improves the mechanical efficiency of the failing heart At the present time there is good evidence that this results not from an action on free energy release but by correcting a defect of free energy utilization We presented evidence that cardiac glycosides act on the con tractile protein actomyosin as well as on the cell membrane We are of the opinion that the two basic actions are inseparable and that the glycosides act through a common mechanism the trins port and distribution of electrolytes across the cell membrane It is very difficult to implicate changes in Na and k transport) in the mode of action of digitalis as these agents produce changes in ton distribution similar to those that occur in congestive failure The effects of digitalis on Cr exchange appear far more significant Present evidence indicates that digitalis increases the available ionized calcium in the vicinity of the contractile apparatus either by increasing its rate of inward movement across the membrane or by releasing it from binding sites in the membrane or myoplasm By increasing the available ionized Ca in the immediate vicin ity of the contractile proteins digitalis would act to enhance the existing interaction between these proteins Ca may function by establishing more cross links between the overlapping filaments or it may act to stimulate ITPase activity which would increase the probability of interaction The sum total effect is to make the interaction between the contractile proteins the same per unit time in the failing heart as that in the normal heart even though tle! overlap of these filaments is considerably less Figure 16 illustratey this important point It is well I nown that the systolic effects of the cardiac glyco siles are only temporary Apparently this is not the result of the development of tolerance as the toxic manifestations are evident ·102 Chemistry of Heart Failure Z A MYOSIN FILAMENTS ATPase SITES ATP SITES ACTIN FILAMENTS B INTERACTION (CROSS LINK) Z -H A Figure 16 Hypothetical interaction between (ilaments in normal (1) and failing (B) myocardium at the dose levels originally employed According to the sliding model digitalis glycosides would be effectie only as long as suflı cient overlap exist betrieen the actin and myosin filaments with further stretch interaction diminishes or may even be elumınited in some fibers When interaction in a sufficient number of fibers is absent intractable congestne heart failure would become est dent and the beneficial effects of digitalis would disappear We feel that this is a rather provocative hypothesis is to thic nature of congestic failure and the mode of action of digitalis At the present time there are no studies available on the ultrastruc tural changes in the myofibril accompinying the desclopment of heart fulure Additional research preferably along the line of the ·Chemisin of Heart failure 103 Huxleys will be needed before we have a clear and exact picture of the nature of the physico-chemical events responsible for this intriguing clinical syndrome NETENENCES 1 Hajdu S and Leonard E I he cellular basis of cardiac glycoside action Pharmacol Net 11 173 1979 2 Frank 0 Zur Dynamik des Herzmuskels Zischer Brol 32 370 1893 3 Starling E H Linacre Lecture on the Lan of the Heart London Longmans 1918 4 Katz L N Analysis of the sceral factors regulaung the perform ance of the heart Physiol Rei 35 91 1953 5 Sarnoff S } lyocardial contractility as described by ventricular function curies Physiol Rer 35 107 1995 6 Fenn WO and Marsch BS Muscular force at different spects of shortening y Plzsiol 85 277 1939 7 Fenn W 0 The relation between the work pcrtormed and the energy liberated in muscular contraction Physic' 58 373 1924 8 Harrison TR Lalure of the Cuculation Baltimore Williams ant TV:lkins 1935 9 Benson E S Composition and state of proten in heart muscle of normal dogs and dogs with experimental myocardial faslure Curc Research, 3 221 1955 10 Clarke NT and Moscher R E. The water and electrolyte con tent of the human heart congesuite heart failure wath and without digitalization Circulation 5 907 1952 11 Harrison TR Pilcher and Lwing G Studies in congestive heart failure IV The potassium content of skeletal and cardiac muscle / Clin inzestigation & 325 1930 12 McDowall R S Munro A F and Zayat AF Sodium and cardiac muscle 1 Playstal 130 615 1955 13 Niedergerke R and Harris ) Iccumulauon of calcium (or strontium) under conditions of increasing contractility Nature 179 1068 1977 14 hapeller Rand kutscherz Aichenbergen H Uber den Calcium gehalt des Herzmuskels Biochem Ztschy 193 400 1928 15 Haxles AF and Perchez L) The maximum length for can traction in strated muscle Physiol 146 55P 1959 ·Chapter / TIBRILLATION A monograph on the chemistry of heart fulle would hardly be complete without ? consideration of fibrillation It is well Inoun that fibrillation is usually the terminal event in many types of tailure both cute ind chronic By 1900 ventricular fibrillation hd been described by Erichsen (1812) Hoffa ind Ludwig (1850) and I 10.ndolf (1894)3 in his perfused heart preparition Physiologie mterests as limited and its clinical counterpart w7s not suspected Heunglin 1906 11 the Physiological Congress in Heidelber. demonstruedi thit in excess of potassium inhibited fibrillation of the polused heist and that a subscquent perfusion with normal Rm.crs solu tion restored the rhythm to normal There are now wailable a number of chic mc ?) and physical methods for producing fibrillation In atu? Rothbr.tr ad Winterbergu in 1910 produced it by rapid stimulation I ens und collaboratorsa in 1920 mduced it by rhythmic summulation rusın, te> z critical rute betn een 350 and 500 per minute and Indrus and Carter produced it in dogs by a single stimulus at the end of the refractory period during 12,77 sumulation In 1937 Mech Hatlian ny and Orthe procluced ventricular fibrillation by the administration of epinephrine in conjunction nith cyclopropune anesthesi? Nahum and Hofl'ın 1910 product atrial fibrillation with the application of 1cetyl A methyletime to localized regions on the arni surface Sherf Romino luni 1101710 produced both flatter and fibrillation by injection at a dilute solution of acontine or by applying crystals of contine in the atrial surface West Turner and I onih noted occurremes of artlıythmias is hen the inter al between stimuli 175 such that the 101 ·Chemiiy of Heart Ialure TO larter fell in the realitc refrsery period. The orrlıythos listed fess seconds to several minutes und were reported in exeur regularly in the presence of ccclcholinc Burn l'urghan Will1973 m Wilher? excriberi a method by which kibrillation could be induced and turned off at all by Stimulating atrit of the dog licart lun, prepiration perfusca «ach acetylcholine Later Holland and Burrit produced the arrhythmin in solaser rabbit 2017? by stimulating at high frequency m the presence of actişlcholine The product1033s of fibrillation in this preparation was clependent upon three factors (1) the presence uf a le concentration of potassium in the medium (2) the presence of a lugli concentration of netylcholme and (3) ivrief klestrual stimulation at a high rue (600 to 1200 per minute) Theories of Fibrillation The first md ollest exp?107 atsast of fibrillation was offered by Engelman' in 189) He proposed the existence of a mmber of simultaneous stimuli prxcluding Roxi in the herrr each tasing its own unirmisit shythmurity and operatin, Independently Ingelmın s theory was ind in the assumption that fibrillation was the result ot the heart existin., in 7 stare al increase excitability Winterbergi extended tlusionc ept ind pro posed that bicause of the increased exuitability the heart fibers became inclependently rhythmı 11 Engelman s hypothesis was soon abandoned when it was shown by Vz. Williamasis that de creased excitability was alw an important factor in the causioon and maintenance of the disorder Lothberger and Winterber,' 10 191 i proposed another theory accordime to which flyrıllanon was due to an extremely rapu unifocal tachysystole Fibrillation in their view was merely ? tachy cardia of exceptionally rapid rue They envisager the existence of a single ectoipic for us ot hul wherent ifrythin which discharged repetitisely and therefore acted as a pacemaker Thus theory became known as the ectopic focus theory of fibrillation It boue the samų time Mines? and Carreyas proposed another mechanisin the souilled cruis inosement theory of fibrillation The theory is based upon the se entry of an impulse into an area of tissue that had responded pres rously to the same ·106 Chemistry of Heart Falue excitation ne The existence of a circhis movement of excitation has experimentally demonstrated by Garrey This hypothesis had its ongin uith the evidence presented by Porter that an inermuscular block would deflect an impulse and Cause it to pursue an abnormal path Mayer ' in 1908 firse observed that if an excitory wave started in one direction only in a ring of muscular tissue of the jelly fish it would triel for a prolonged period of time Garrey is and Minesis demonstrated this phenome non in rings of atrial and sentricular muscle i eivis adı inced the idea that circus movement would arise ind pass around 7 ring of atrial tissile surrounding the junctions of the inferior and superior vena cavae Honeser the existence of such a muscle entity has been dispuced Recently the ectopic focus theory of fibrillation has been revaved primarily as a result of the studies of Schert? and Prinz metal and collaborators Scherf was able to produce atrial fibril lation by copıcıl application of acomtine to the exposed atrial surface of the clog The ectopic focus theory clreus strong support when it becaine er udent that aconitine induced fibrillation could be arrested by cooling the site of application Fibrillation tias also produced by the action of acciyle bolige It differed from that produced by aconitine in that a similar inhi bition at the site at thich acetylcholine 175 applied did not arrest the condition Hotejer simultaneous inhibition of the Si und AV nodes usually stopped fibrillation produced by both copacilly applied acetylcholine and by means of electric 11 stimulation This difference in response suggests that the mechanism of fibrillation is not due to a single agency At least in the case of atrial fibrillation two forms can be distinguished one with a single focus and the other with multiple suistuiming fou The two forms fouerer cannot be differentired upon inspeccion of thic electro cardiogrın hitz and Pich s prefer to visualize sentricular {iltill? tion as a state in nuch the heart has been dised into a mulu plicity of ectopic foci with numerous individually acting units Ionic Mechanisms and Filprillation "The ionic basis for changes in the electrical properties of the hit 175 during fibrillanon is now available in 1935 helir and Hooler observed nr 111516it ·Chemistry of Heart rorluse rise of h in coronary sinus blood of fibrillating dog hearts They concluded that readily diffusible h ions were associated sith the phenomenon of 1entricular fibrillation Vore recently these find ings have been confirmed and extended in our own laboratory working with isolated rabbt atria In the initial study data serey obtained which suggested that fibrillation only began when the rate of nee loss of h and gain of Na exceeded a critical one For k this rate sas of the order of 20 to 25 m Voles per kgm set tissue per minute The rate for Na could not be established with accur acy but it appeared to be considerably higher Later isotope suudies resealed that the net loss of h resulted from an increased efflux of h influx tas slightly increased or unaffected The net gain of Aa tltat occurred resulted from a marked increase in the insard movement of Ma even though out floss tias also increased to some extent Since k influx was not greatly changed during fibrillation it was reasoned that an increased membrane permeability to h was not the prime factor insoled It was postulated that a more likely cause was the marked Increase in the inward movement of Nauh leaving the tissue in exchange Several other points of interest were also established The changes in \a and h fluxes were only transient in nature with flsx rates returning to normal even though fibrıllarion continued The changes in Na transport persisted for longer periods of time than those for h This indicated that the increased membrane permeability to Massas ssvolsed primarily with the initiation of fsbrillation Koneser these studies did not rule out the possibility that an increased Na permeability was a factor of importance in the maintenance of the arrhythmia Calculations revealed that the positie charge entering the atria as Na exceeded that which was lost as This suggested that permeability to an anson possibly Ci was also increased Studies 30 using C]se showed that the net gain of positive charge (difference between Na upishe and h loss) was balanced by a net gain of C} These findings led to the follos mg rather crude picture of the nature of ionic events accompanying fibrillation The onset of fibrillation probably results from a marked increase in the inward ·108 Chemistry of Heart Failure IS to continue movement of No jons If the atmnl cells are to respond repeatedly and 11 1 fast rate there inust be some device which rapidly inacti vates the ink ard Na movement Thint is the process of No inicii vation (see Chapter V) must be greatly accelcrued if the irrythmia an increase in the outward movement of or innard movement of Cl or a combination of both would be pos sible mechanisms The outward movement of k may contribute Initially to the inactilation process whereas the increased in and movement of C1 may make a predominant contribuuon to the process of inactilitani once the arrlıythmia las persisted for some tim Recently it 117s been shown that ( 7 ions determine the extent to which the inward movement of Cland outflow of a con tribute to the inactivation process ! At high Ca concentrations the inflow of C) is the predominating factor According to this scheme the antiarrhythmic agents should act by depressing the inward movement of Ne lhe 11 07ble evidence to date would indicate that such is the ( 15e Metabolic Events and Fibrillation Thcielne been 1 imce number of studies on changes in oxygen (sumption and subs strate utilization during ventricular fibrillation 13 34 The curence indicates that as long as the ventricles are supphed with ?»Boscut by in extracorporeal pump oxygen consumption extraction of enen tial substrates and the content of energy rich compoun yr wall tithin normal limits REFERENCES 1 Frichsen J E On the influence the coronary circulation on the action of the heart London Mi Ga eite 2501 181. 2 tloffa +1x Ludwig C Einige neue Versuche ulter Hube wegung 7 tsehr mit died 9 107 1830 3 I 1n endorſt o Ucher dus ll ogen oder Flimmern des Sternsis Arch ges Physiol 70 281 1898 4 Hering HL Demonstration der Aufhebung des Homens durch Injekton von hCi Lusungen Deutsche mer lletlusher 33 1507 1907 5 Rothberger ] and it interberg II Ulser ilas I kectrokardio,ram bei Flimmern der Torholt dich ges Physiol 131 7 1910 ·Chemistry of Heart I ailure 6 Lewis 'I cul It S and Stroudl 11 1) Observationis tipon fluier ani fibrillation I ut Ihe ndlure of auricular Ilutus Heart 191 3920 Andrus E G und Carter 11 The refractory period of the normally letting dogs atiricic #21h noll on the occurrence of tursculo librıltumn (olioung 2 single stimulus 1 rxper Ved 51 937 1930 8 Veel M J Hazlitkay II Ran Orih OS Liicts of ether chloroform and clopwopine on rulanc 3utomatical ? Phar macol Exper Therap 61 2:0 1937 9 Tahun LH and Floff HE Prolaction of curicular dibralt: tion by application of acetyl 8 methylcholsse chloride to local izcu regions on the auricular surfcam llysol 179 1.28 1910 10 Scharf D Romano } } 100 l (IT inota R L yerimentat studies on pericular flutter and ruricular fill tion Heart) 36211 1948 11 West TC Turner L3) and Loomis 1 A Lffects of acetyl cholinc on mechanical and clinical properties of isolated riblitt aurice Their selstrouslup to the finests of arrhythmus , Pharmacol 4 Leper Cherago 11 172 1971 19 Bumn , H Vaughan Willems Ł M und Walker ve I he ellects of acetylcholine in the hic art lung preparation including production of auricular fibrillation | Physiol 128 277 1935 19 }}olland TY 6 and urn J IE Iroduction of fibrillation in iso lated atrı of rabbit hcart Brut MI J 1 1031 1937 14 Engelman I W Utber den Einfluss der Systole auf die Motor ischc Leistung in der Herzkammer mit Bemerkungen zur Thcoric allorlıythmischer Herzstocrungen Arch Les Plynol 62 513 1895 35 Winterberg H Ueber Herzflimmern und seine Peeinflussung durch hampler Zisch exper Pathol Therap 3 182 1906 16 VacWilliam 4 On the phenomena of inkubation in the mam malıın lieart J Physiol 9 345 1888 17 Rothberger c } and Winterberg II Veber Vorhofflimmern und Vorhofflanern Arch ges Physiol 160 42 1914 18 Wines GR On circulating excititions in heirt muscle ind their posssble relation to tachycardia and abrillauion Tr Roy Soc Canada 8 13 1914 ·110 Chemistry of Heart Tailure 19 Garrey WE The nature of fibrillary contraction of the heart Its relation to tissue mass and form Am J Physiol » 397 1914 20 Porter W T Ueber die Frage eines Coordinations scentrums im Herzventrikel Arch ges Physiol 55 366 1894 21 Mayer AG Rhythmucal palsation in Scyphomedusae Papers from Tortugas Laborator Carnegre Inst II ashington 1 115 1908 22 Lewis T Auricular fibrillation Brit Nj 190 1921 23 Scherf D Schaffer AI and Blumenfeld S Mechanism of flat ter and fibrillation A A A Arch Internal Med 91 333 193 21 Prinzmetal M Corday £ Brill I C Oblath R 11 Ind kruger HE The Auricular Arthythmias Springfield III i homas 1952 25 hatt LN and Pick A The mechanism of auricular flutter and auricular fibrillation Circulation 7 GOL 1993 26 hehar N D and Hooker DR Evidences of an alccred tissue state in ventricular fibrillation Am J Physiol 11? 301 1933 27 Holland WC Potassium exchange in atrial fibrillation Im / Physiol 190 G3 1997 28 Klein R L and Holland WC Na and he chan, in zrial fibrillation Am J Physiol 193 239 1998 29 Holland WC and blein RL Effects of temperaturę Na and h concentration and quinidine on transmembrane flux of 1 and incidence of atrial fibrillation Circ Research 6 516 1998 30 Sekul A 1 and Holland WC Cars and C136 exchange in atriai fibrillation in ) Physiol 197 772 1979 31 Briggs A Hand Holland WC (unpublished experiments) 32 Klein RL Holland WC and Tinsley B Quinidine and undirectional cation fluxes in atria Circ Research & 216 1960 33 Senning ALE Ventricular fibrillation during extracorporal circulation dcta chir scandinav Supplement 171 1 1952 34 Prul H Tlieilen E O Gregg D E Varsh ] B and Cisten Curdiac metabolism in experimental ventricular fibrilla tion Cnc Research 2 573 1954 ·Chapter 1 PERSPECTIVES At the current rue of progress there 15 lutie doube that in the foreseeable future we muy &non the detailed chemistry of most biological processes including muscle contraction When all the chemistry is known we will suill be unable to understand how the processes are effected and how the high state of cellular organization is maintained without a much greater emphasis on physical mechanism in the present monograph the authors have carried the tender from the macroscopic through the microscopto then to the molecular and submolecular level in an empt to understand the processes associated with contraction of the normi? and failing heart We have adhered to the classical view of Frank and Starling that all phenomena associated with congestive heart failure can be explained by the concept of excessive stretch of the myocardial liber resulting from increased demands placed upon the heart Our thesis is that heart and skeletal muscle contract to performi Kork by an interaction between sites on sterdigitating myofila ments in the sarcoinere This interaction appears to be between ATPase sites on the thick myosin fıtıment in the A band and ATP bound to actin in the thun I band filament The chemical correlate of the Frank Starling principle was pictured as a diminisung inter action resulung from gradual withdrawal of the I band filiment from the A band The latter was due to excessive stretch of the myocardial fiber The role of Ca ions to enhance and maintain interaction was emphasized A decrease of Ca ions as is known to occur in con gestive failure should lead to less interaction and wealer con We presented evidence that digitidis acting at the tractions ·112 Chemistry of Heart Failure membrine increased the available in the emurons of the con tractile filiments thereby restoring the normal rate of interiction It was pointed out that with excessive stretch interaction would disappear in some fibers When a sufficient number of fibers stere involved intractable heart failure should appear and the beneficıl effects of digitalis should be lost We briefly reviened some of the recent adı ances in our Inowi edge of fibrillation 1 phenomenon intimately associated 12th heart failure Apparently thus arrhythmia results from the estab lesliment and maintenance of an abnormal membrane permea bilscy to Nz ions Here again Ca plays a very crucial role Viny problems remain to be solved The most inportant is the nature of the physico chemical mechanisma imolved in the development of hypertrophy It is hoped that with the application of the powerful physical techniques available that we will soon Inon more of this intriguing phenomeno ·INDEX Chlori le 636 68 69 90 Cholinesterase cell membrane 37 digitalis 9 passive electrolyte transport role in 37 61 Cro s br Iges 03 A bands 48 enzymes in 390 Acetylcholine cell membrane 57 electrolyte transpert 6! fibrulat on 101 100 Acetyl cocnzyme A 16 2 26 32 Actin 59 of Adenosine diphosphate (ADP) glycolysis 22% oxidative phosphorylation 28 33 Adenos ne tropho phate (ATP) actn content of 53 act ve transport 37 61 actomyosin 54 5 contraction role in 57 9 digitalis effect on 88 89 glycolisis 1 oxidati e phosphorylation 6 33 structure of Adenosine triphosphatase active transport role in 37 64 ligitalis 87 90 memt ane 37 mitochondr a 31 muscle contraction 59 48 9 myosin 2 3 Am o acid metabolism 31 32 Anorta 34 7 16 Antiarrhythmics-mode of action of 109 Delta protein 50 50 Digitalis elf cts on acti e transport 90 adenosine ur phosphate 90 cholinesterase 90 electrolyte metabolism (a h and Ca) 88 91 free energy release 87 ATP 89 glycolysis 87 oxidati e phosphorylation 88 free energy ut lization 88 act 88 actomyos n and ATP 88 89 myosin 88 heart fa ture Iee energy release in 87 89 free energy uulation n 88 89 ose all metabol sm 86 87 p ssi e tran port 90 mode of ction of 101 10% Beri be: 6 Calcium digitalis 89 91 exchangeability in heart 63 excitation contraction couplino 10 heart fa lure role n 79 91 66 intracellular d tribution of 6 localizat on in sarcome e of 10 Cat on transport part cle 6 Elast component 50 51 4 Electrolyte metabolism act re tran port 37 63 64 bioelect ic potentials 66 69 ard ac contract on 66 chlo de 63 90 107 108 dgital s 88 91 ercitat on contraction coupling 69 calc um 70 113 ·214 Chemistry of Heart Failure methods of production 101 10 theories of circus movement 105 106 Ectopic focus 10.) 106 Fret energy-schere of relcase 33 Frank Starling principic 7 97 98 100 Glycolysis reaction dignalis effects on 87 88 efficiency of 29 enzymes in 21 22 phosphate and phospkate acceptors scheme of electrochemical gradients and diffu sion 69 endoplasmic reticulum 71 Hature of stimulus 69 Z line 0 fibrillation 106 103 pacemaker 67 passate transport 37 63 64 potassium 63 64 sodium 63 64 Electron transport system 63 outline of scheme of 28 oxidative phosphorylation and the 26 28 Endoplasmic rericulum excitation contraction coupling 71 microsorues 37 protein synthesis in relation to 37 Enzymes adenosine triphosphatase 34 3 61 cholinesterase 3. 61 90 condensing 22 enolase 2 glutatdate alanate transaminase 32 glutamate asparate transaminase 31 32 herokinase 23 localzation in cell of $s cytoplasm 37 membrane 37 68 microsomes 37 mitochondria 34 37 nucleus 54 phosphoryl glycerskinase 21 phosphoryl glyceryl mutase 24 prutate Linase 21 22 triose phosphate dehydrogenase 21 Excitation contraction coupling electrochemical gradients and diffa $1on 69 endoplasmic reticulum 75 Z line and Ca activation linkage 0 H zone 49 Heart contractile proteins 53 cfficiency of 17 electrolites and contraction 6 66 failure of digitals and free energy metabolism על כן מן elecitolyte metabolism in (la k Ca) 78 999 proteins ! 4 8 theories of 9, tur types of 19 anoria / coenzime lack and homo al 3 balance 76 7) hyperten Be and sal u disas 17 narcotics 77 hypertrophy : 80 memal sase potentials 66 67 atsal ani ventricular sctetne of energy telcas concrust and utiluation by S3 hot of 16 I mcromisin 53 64 ATPase content of S Il pertrophy 9 chemistry of SO RI myocardial ultrastructure in 80 Fatty acids 29 92 bela vridation of og si outline of degradation of 30 Fibrillation sonic basis of tor 108 metabolismo during 109 I bands 49 Inictcalated disc 494 Intracellular distribution of tons 6 66 ·Chemısın of Heart failure 115 Krebs citric acid cycle 25 acetyl coenzyme A 1632 structure of 26 and no acid metabolism and the SI 32 condensing enzyme in 23 efficiency of 29 enzymes of an mitochondria 31 fatty acid metabolism and the 293. scheme of 97 striated 46 sarcomere of 19 filam nts (actin and myosin) 19 50 1ons in GG 10 proteins in actin j' 53 actomyosan 13 1 55 delta protein 50 53 1 56 localization in fibril 54 56 myosin 59 54 tropmyosin 53 ut ut 56 relaxing factor 5 sarcolemma 45 48 ultrastructure 14 48 Myosing of huhne 5 L meromyosin 53 61 cholinesterase content of 61 Nerve role of 4 TPase in active transport in 61 Nucleic acids desoxyribose nucle c acid 34 ribose nucleic acid 34 M line 19 Na nestum 6 66 10 Merubrane potentials 66 69 Microsomes 37 Mitochondria ATPa e 31 effect of drugs on 34 electrolytes in 66 electron microraph of 3 localization of enzymes of 33 34 37 permeability of 36 tridimensional model of 36 Muscle contraction ATP and ATPase role in 5 55 changes in striations during 51 theories of 56 One filament 56 58 sl ding model 58 60 in heart failure 100 fibers 44 45 branching of in heart 44 45 di meter of 46 fibrils cross striation and ultrastructure 48 50 chan es in during stretch and con traction 50 51 d ameter of 44 electron micrographs of 45-49 A band cross s ction 49 isolated myof bril 48 myocard al branching 4 myocard um and motochond ia 47 Phosphagens 14 Phosphocreatine 14 16 76 77 88 structure of 4 Potassium active transpo t of 63 64 dgitalis 89 90 fibrillation 104 107 108 intracellular d stribution of 65 66 pacemaker 65 passive transport of 63 64 resting potential 66 68 rol in heart failure of 89 91 99 101 Sarcolemma 44 45 48 Sodium action potential 68 69 active transport of 63 64 digitalis 89 90 f brillation 107 108 intracellular distribution of 65 66 pacemaker 6 passive transport of 63 64 role in heart failure of 89 90 99 101

·116
Chemistry of Heart failure
Thermodynamics 10
common reactants 14
concept of energy nich bonds 15
concept of free energy II
coupling mechanisms 13
efftciency of the heart 17
electromotise force 15
entrop: 12
equilibrium constant and mass achon
1' 13
exergonic and endergonic reactions 1°
13
free energy and oxidation 15 16
free energy of hydrolysis 16
internal energy 12
las of mass action 12
spontaneity of chemical change 13
standard electrole potential 16
standard free energi 13
work of the heart 16
Thsrotoricosis 6 17
Tropomyosin 53
protein 56 56
Z line 481