ABSTRACT The effects of cyclopiazonic acid (CPA) on the Ca2+ -dependent ourward K+-cur-rent [IK(ca)] were studied using whole-cell and single-channel patch-clamp techniques. Depolarization (pipette potential range from - 20 to - 120 mV)induced a outward Ik(ca) with a conductance of about 40 pS in the cultural aortic smooth muscle cells from SHR and WKY. 10 ?mol ? L-1 CPA significantly enhanced these currents and prolonged the mean open time of the channels. This effect of CPA was completely blocked by glybenclamide, a K+-channel block-er. In the whole cell recording experiments, CPA increased the amplitude of outward K+-current. This effect of CPA was Ca2+-dependent and completely blocked by glybenclamide. There was no any significant difference between the effects of CPA in SHR and in WKY. These results suggest that the functional change of vascular smooth muscle in SHR doesn't appear to be related to Ik(ca).