ELECTROPHYSIOLOGICAL ANALYSIS OF MYOCARD MEMBRANE PROPERTIES DURING PLATEAU OF ACTION POTENTIAL, EXISTENCE OF A SLOW INWARD CURRENT IN SOLUTIONS WITHOUT DIVALENT IONS

In isolated perfused rat heart, electrophysiological analysis of myocard membrane properties in the absence of divalent ions during the plateau of the action potential, shows that: 1. The maintenance of the membrane potential at plateau level (near E=0 mV) does not depend on the action of an active cellular potassium absorption mechanism dependent on metabolism. 2. The plateau potential depends on the external sodium concentration, the membrane behaves like sodium electrode. 3. The plateau potential is little or not at all modified by tetrodotoxine, but totally abolished by manganese ions. A Voltage clamp of frog atrial muscle shows, under identical conditions, the existence of a slow inward sodium current responsible for long duration responses. This current is not modified by tetrodotoxine, but suppressed by manganese ions. So, under similar experimental conditions (Ca++, Mg++, free solution) the existence of long duration sodium responses in the rat proves the existence of a slow channel identical to that previously described in the frog. © 1969 Springer-Verlag.