Effects of thrombin on single calcium channels in frog ventricular cells.

Single calcium channel (Ca channel) currents were measured using the patch-clamp technique in isolated ventricular myocytes of the frog (Rana esculenta). Sodium was used as the charge carrier. After formation of cell-attached patches, the proteolytic enzyme thrombin was added to the bath solution, where it increased the amplitude of the averaged currents more than twofold, by decreasing the number of empty sweeps and reducing the time constant of the slow exponential term of the shut-time histogram. Single channel conductance was not changed by thrombin. If the activation kinetics of the Ca channels are described by the commonly used C1-C2-O model, where C1 and C2 indicate closed states 1 and 2 respectively and O denotes the open state, thrombin increases the open-state probability in the non-empty sweeps by increasing the rate constant (k1) for the transition from C1 to C2. It is shown that thrombin acts via an H-7 blockable pathway.