Separable Spike and Plateau Action Potentials and their Roles in Contraction of Frog Ventricle ∗

Abstract

Summary

The compound nature of the ventricular muscle action potential was demonstrated. Two thresholds, one for spike and the other for plateau generation were observed in the frog ventricles under action of Mn²⁺, and even more clearly in hypertonic Ringer solutions containing glycerol and Mn²⁺. Twitch contractions occurred only with appearance of the plateau. Tetrodotoxin eliminated the spike, leaving a plateau-like response behind. The Na⁺-spike is thought normally to trigger the plateau response which relates somehow to Ca²⁺-influx and release and thus to the initiation of contraction.