The ionic basis of membrane excitation in ordinary myocardial fibers: some aspects of the sodium and calcium conductance

Abstract

Ionic currents in heart muscle are usually described in terms of the Hodgkin-Huxley theory for nerve fibers. Attention is paid to some aspects of the sodium and calcium conductance which seem to be specific for heart muscle: 1) recent findings indicate that repriming of the sodium and calcium conductance in heart muscle cannot be described as the reverse process of inactivation; 2) the existence of an important calcium current is well established, but controversial findings have been obtained for the time constant of inactivation; 3) Na and Ca interact in determining the slow channel current. Depending on the external Na and Ca concentration, antagonistic as well as synergistic effects may be obtained. An explanation is offered for these contradictory results.