Two types of Ca channels in smooth muscle cells isolated from guinea-pig taenia coli

1) Two types of voltage dependent Ca channels with different conductances and inactivation kinetics were identified from cell-attached patch clamp recordings. One type, with a larger conductance of 25pS, had a threshold of activation near -40mV and the mean current inactivated slowly. A second type of Ca channel, with a smaller conductance of 12pS channel, but the averaged mean current inactivated rapidly. 2) Cadmium ions inhibited the large conductance Ca channel currents, while the small conductance Ca channel currents was not blocked. 3) Large conductance Ca channel current selectively inhibited by dihydropyridine derivative, Nifedipine. Small conductance Ca channel current is abolished in dose dependent manner by pyrethroid insecticide, tetranethrine.