Ca-channel currents in isolated frog ventricular cells are increased by thrombin.

Effects of the proteolytic enzyme thrombin in the modulation of cardiac Ca-channel currents were examined in single ventricular cells from frog myocardium, using the whole-cell voltage clamp technique (1). Application of 3.8 . 10(-9) M thrombin to the bath increased the peak of the Ca-channel current by 84 +/- 35% (8 cells). Hirudin (31.10(-9)M), a specific thrombin inhibitor, blocked the thrombin-induced increase of this current. The increase in the current can be made responsible for the measured positive inotropic effects on frog heart of thrombin.