Excitation and Excitatin-Contraction Coupling in Cardiac Muscle

In compliance with editorial instructions, this reviewer will discuss only a few highly selected topics related to cardiac cellular electrophysiology and excitation-contraction coupling which are either currently controversial or, in his opinion, in need of a renewed perspective. Amid the multitude of recent developments in muscle physiology there appear four aspects of cardiac muscle behavior which are of specific interest to the author. They are (a) a challenge of the applicability of the ionic hypothe5i5 to cardiac muscle ba5ed on the per5istence of electrical and mechanical responses in nonionic media, (b) the occurrence, in the types of cardiac muscle whose action potential possesses a plateau, of a membrane conductance which during the plateau falls to a value equal to or less than its diastolic value, (c) the existence of a correlation between the duration of the membrane potential duration and the rise time to peak tension in several but not all types of cardiac muscle nor under all conditions, and (d) the finding that muscle tissue placed in hypertonic media undergoes an apparent uncoupling of electrical and mechanical events. Without further examination of the available data, it is intriguing to ask whether all these phenomena might not be manifestations of the basic properties of the excitation-contraction coupling mechanism. This reviewer will attempt to place these observations in a perspective with which to evaluate this question.