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.