Block effects of IHC-72 on calcium current in single guinea pig cardiac myocytes.

Block of the calcium current by IHC-72 in single ventricular myocytes isolated from guinea pig was studied by using the whole-cell patch clamp technique. IHC-72 in micromolar concentrations depressed the calcium current in a concentration-dependent manner, with an IC50 of 0.06 +/- 0.02 mcmol/l. After application of IHC-72 the peak calcium current began to decrease within 1 min and reached a steady state within 10 min. The current-voltage relationship for the calcium current peak was not changed by IHC-72, but the amplitude was significantly suppressed. Although IHC-72 did not alter the time course of inactivation of the calcium current, it shifted its steady state.