A dual effect of cardiac glycosides on Ca current in single cells of frog heart

The effects of cardiac glycosides (1 μM ouabain, 50 μM dihydrooubain, 1 μM strophanthidin) on Ca current (ICa) were investigated on Csloaded single frog ventricular cells using the wholecell patch-clamp technique (9). Cardiac glycosides exert both inhibitory and stimulatory effects on ICa in 20 Cs Ringer solution, but have only a stimulatory effect in O Cs, when the Na,K pump is blocked. The inhibitory response seems related to the inhibition of the Na,K pump by glycosides. The stimulatory effect on ICa may contribute to the positive inotropic effect of cardiac glycosides.