Regenerative repolarization of the frog ventricular action potential: a time and voltage‐dependent phenomenon.

1. The regenerative repolarization process has been examined in frog ventricular myocardium using a single sucrose gap voltage clamp technique. 2. Application of brief (30‐150 msec) anodal voltage clamp pulses during the plateau of the action potential revealed a 'threshold' potential region for immediate repolarization. The response to anodal clamp pulses was not all‐or‐none but was graded. 3. The threshold potential was strongly dependent on the duration of the test voltage clamp pulses and was more negative for shorter clamps. 4. Regenerative repolarization was also observed in the presence of tetrodotoxin. 5. No threshold for immediate repolarization was observed with very short clamps (2‐20 msec in duration). Instead the membrane depolarized upon release of each clamp pulse. 6. Theoretical showed that the de‐ and repolarizations observed after test clamp steps are not due to geometrical properties or inhomogeneous potential distributions. 7. The results suggest that the instantaneous I‐V relation of the membrane during the plateau may be linear.

[1]  Walmor C. De Mello,et al.  Chapter 12 – The Healing-Over Process in Cardiac and Other Muscle Fibers , 1972 .

[2]  E. Benson,et al.  THE ULTRASTRUCTURE OF FROG VENTRICULAR CARDIAC MUSCLE AND ITS RELATIONSHIP TO MECHANISMS OF EXCITATION-CONTRACTION COUPLING , 1968, The Journal of cell biology.

[3]  J. Sommer,et al.  Cardiac muscle. A comparative ultrastructural study with special reference to frog and chicken hearts. , 1969, Zeitschrift fur Zellforschung und mikroskopische Anatomie.

[4]  I. Tasaki,et al.  INITIATION AND ABOLITION OF THE ACTION POTENTIAL OF A SINGLE NODE OF RANVIER , 1956, The Journal of general physiology.

[5]  M. Morad,et al.  Ionic membrane conductance during the time course of the cardiac action potential. , 1977, The Journal of physiology.

[6]  R. Orkand,et al.  Excitation—contraction coupling in frog ventricle: evidence from voltage clamp studies , 1971 .

[7]  A. Hodgkin,et al.  A quantitative description of membrane current and its application to conduction and excitation in nerve , 1952, The Journal of physiology.

[8]  S. Weidmann,et al.  Effect of current flow on the membrane potential of cardiac muscle , 1951, The Journal of physiology.

[9]  D. Noble A modification of the Hodgkin—Huxley equations applicable to Purkinje fibre action and pacemaker potentials , 1962, The Journal of physiology.

[10]  S. Weidmann,et al.  Shortening of the cardiac action potential due to a brief injection of KCl following the onset of activity , 1956, The Journal of physiology.

[11]  R. Niedergerke,et al.  Structures of physiological interest in the frog heart ventricle. , 1972, Journal of cell science.

[12]  H. Curtis,et al.  ELECTRIC IMPEDANCE OF THE SQUID GIANT AXON DURING ACTIVITY , 1939, The Journal of general physiology.

[13]  D. Noble,et al.  The Conditions for Initiating "All-or-Nothing" Repolarization in Cardiac Muscle. , 1963, Biophysical journal.

[14]  D. Noble,et al.  Current—voltage relations of Purkinje fibres in sodium‐deficient solutions , 1963, The Journal of physiology.

[15]  R. Tsien,et al.  Some limitations of the double sucrose gap, and its use in a study of the slow outward current in mammalian ventricular muscle. With an Appendix , 1974, The Journal of physiology.

[16]  J. Trank,et al.  Equivalent Circuit of Frog Atrial Tissue as Determined by Voltage Clamp-Unclamp Experiments , 1971, The Journal of general physiology.

[17]  B. Hoffman,et al.  PROPAGATED REPOLARIZATION IN HEART MUSCLE , 1958, The Journal of general physiology.

[18]  G W Beeler,et al.  Voltage clamp experiments on ventricular myocardial fibres , 1970, The Journal of physiology.

[19]  D. Noble,et al.  The voltage dependence of the cardiac membrane conductance. , 1962, Biophysical journal.

[20]  A. J. Brady,et al.  The sodium‐potassium hypothesis as the basis of electrical activity in frog ventricle , 1960, The Journal of physiology.

[21]  M. Vassalle Analysis of cardiac pacemaker potential using a "voltage clamp" technique. , 1966, The American journal of physiology.