Transitions between 2:1 and 1:1 responses in cardiac muscle induced by added stimuli
We demonstrate experimentally that transitions can be induced between stable coexisting response patterns in bullfrog ventricular myocardium by means of a single pulse injected into the stimulus train. We find that two distinct ranges of stimulus timings will elicit transitions from a 1:1 state, in which one stimulus elicits one response, and a 2:1 state, in which every other stimulus elicits a response. We also observe two distinct types of 2:1→1:1 transition. These transitions are differentiated by their transient behavior while settling from one stable state into another. We characterize these transitions, and the ranges of added stimulus timings which produce them, both experimentally and with two simple models of cardiac dynamics.