Modification by nicorandil and carbachol of the inward calcium current in single cells of the guinea-pig heart.

Effects of nicorandil and carbachol on the inward calcium current were studied in single heart cells isolated from the guinea-pig using a collagenase dispersion method. The inward calcium current was obtained in the absence of outward potassium currents by intra- and extra-cellular perfusion of the cell with Cs+-solutions. Nicorandil (0.3 mM) failed to modify the inward calcium current in the atrial cell. In the ventricular cell the inward calcium current was increased by isoproterenol (1 micron). The augmentation of the inward calcium current was abolished by carbachol (1 micron) but was not changed by nicorandil (0.3 mM). From these results it can be concluded that nicorandil has no direct effect on the inward calcium current even when the inward calcium current is previously augmented by isoproterenol.