Components of the cardiac action potential

Two components have been observed in the intracellular action potentials of frog ventricular strips under conditions of impaired transmission. The strips were bathed in Ca-free, Mg Ringer's solution and were subjected to passage of current pulses through their length. Under these conditions a "notch" gradually developed at the beginning of the plateau and separated the action potential into a spike and a slow wave. In any given cell, the notch was often more prominent when the conditioned strip was stimulated from one end than from the other. Occasionally a spike in isolation spontaneously alternated with a spike plus slow wave response. The slow waves were generally graded in duration and magnitude with stimulus intensity or duration. The results are discussed in terms of a possible junctional response at the intercalated disc.