Hysteresis phenomena in excitable cardiac cells analyzed by a microcomputer system

The authors test the hypothesis that hysteresis phenomena may exist in normally depolarized cardiac cells when an external stimulation parameter is allowed to changed. The underlying assumption is that cardiac cells may have intrinsic properties involving the memory of past events, independent of pacemaker and nonpacemaker interactions. This kind of behavior is found in 11 of 14 quiescent sheep Purkinje fibers which were rhythmically driven by depolarizing pulses, and in 13 of 14 isolated guinea-pig ventricular myocytes in which transmembrane potentials were recorded by the whole-cell current-clamp technique. Changes of pulse duration and temperature modulated the degree of hysteresis. The authors conclude that hysteresis may express some kind of memory in cardiac cells, probably enhancing stability against noise in the vicinity of threshold, while allowing cardiac cells to remain excitable at the lowest possible level of energy expenditure