CHAPTER 11 



Cellular electrophysiology of the heart' 



J. WALTER WOODBURY 



Department of Physiology and Biophysics, University of Washington 

 School of Medicine, Seattle, Washington 



CHAPTER CONTENTS 



The Resting Cell Membrane 

 Passive Ion Movements 



Membrane structure 



Membrane capacitance and resistance 



Ion equilibrium potential 

 Active Na^-K^ Transport 



Active transport 



Energetics 



The Na^-K"*" exchange pump 

 Generation of the Resting Potential 

 Effects of Changes in External Ion Concentrations 

 Potential 

 The Active Cell Membrane 

 Membrane Current 



Capacitative current 



Membrane voltage clamping 

 Ion Currents at Constant Voltage 



Separation of sodium and potassium currents 



Sodium and potassium conductances 



Inactivation and activation of sodium conductance 

 Quantitative Description of Nerve Behavior 



Kinetics of conductance changes at constant voltage 



Prediction of the action potential 



Threshold and anodal break excitation 



Ionic exchange 



Refractory period 



Propagated action potential 

 Membrane Properties of Cardiac Cells 

 Intracellular Recording 

 Depolarization 



Activation and inactivation of sodium conductance 

 Repolarization 



Factors affecting repolarization 



Superimposability of action potentials 



Slope conductance during repolarization 



Slope and chord conductances 



Slope conductance and current, voltage relationships 



Possible mechanisms of repolarization 



Hypotheses of repolarization 



Auto-rhythmicity 



Effects of vagal and sympathetic stimulation 

 Excitation-Contraction Coupling 

 Passive Membrane Properties and Intercellular Transmission 

 Structure of Cardiac Muscle 

 Analysis of Two-Dimensional Electrotonus in Atrium 



CONTRACTION OF THE HEART is iliythmic, abrupt, 

 maximal, prolonged, and nearly synchronous in all 

 the cells surrounding a chamber (fig. i). In contrast, 

 contraction of a whole skeletal muscle is smooth, 

 graded, and of variable duration, its component 

 motor units twitching asynchronously. In their 

 patterns of contraction the two types of muscle differ 

 in ways which are consonant with their particular 

 functions. The pattern of cardiac muscular con- 

 traction insures the efficient ejection of blood. The 

 force exerted by a skeletal muscle can be varied 

 smoothly and continuously over a wide range to 

 meet the changing demands of bodily motion. The 

 similarities between the two kinds of muscle are 

 that they are both contractile and that, normally, 

 the degree of activation of the contractile substance 

 depends on the membrane potential. 



In cardiac cells, the duration of contraction is 

 proportional to the duration of the action potential; 

 and the sequence of their contractions is determined 

 by the characteristics of the intercellular transmission 

 processes. Figure i shows simultaneous recordings 



'Aided by Grant B-1752, from the National Institute of 

 Neurological Diseases and Blindness, U. S. Public Health 

 Service. 



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