CHANGES IN THE CONFIGURATION OF THE RABBIT ATRIAL ACTION POTENTIAL AFTER VARIOUS PERIOD OF REST

Abstract

This paper describes the effects of varying the time between excitations on the configuration of the action potential of the rabbit atrium which was not spontaneously active. Whenever the preparation had been kept at rest for a long period, the plateau phase of the first action potential was diminished and a spike-like potential with a long-lasting after-depolarization was obtained. The plateau phase appeared in the action potential elicited by the second shock at the stimulus interval of less than 30 sec. The duration of the plateau phase increased as the interval decreased until it reached about 0.5 sec. Differences in the rate of depolarization between the first and second action potentials thus obtained were very small when the second action potential was elicited beyond the refractory period of the first. By repetitive stimulation at definite intervals, a more prominent plateau phase was developed through a transient period, starting from the first spike-like potential to the final potential with a constant configuration corresponding to the particular stimulus interval. From these results, it is suggested that a prolonged action potential of a periodically excited heart may result from the longlasting small after-depolarization following each preceding action potential. Some possible underlying mechanisms were discussed.