Ryanodine has no effect on the Ca current in single ventricular cells of guinea-pig.

The Ca current was isolated and the effects of ryanodine were examined in Cs-loaded guinea-pig ventricular myocytes. The time course, amplitude and voltage dependence of the Ca current were not affected by the external or internal application of ryanodine, thereby suggesting that this alkaloid has no direct action on the Ca channel and that the inactivation of the Ca channel is not affected by Ca released from sarcoplasmic reticulum, at least under the present experimental conditions.