The voltage-dependent effect of 1,4-dihydropyridine enantiomers on Ca channels in cardiac cells.

We studied voltage-dependent binding and action of 1,4-dihydropyridine enantiomers (Sandoz (+)-(S) & (-)-(R)-202-791) in intact cardiac cells. Drug action was studied by patch clamp method. (+)-enantiomer primarily prolonged open time of Ca channel, thus enhancing Ca currents, while (-)-enantiomer predominantly favored closed state of the channel, reducing the currents. Electrophysiological study also revealed that steady-state inactivation was greatly enhanced by both enantiomers. Therefore, it seems that both enantiomers have a capability of activating and blocking effects. Strongly voltage-dependent binding affinity of these enantiomers was revealed by displacement of 3H-(+)-PN200-110 with each enantiomers. Binding affinity of both enantiomers in depolarized cells was much higher than in polarized cells. These results indicate that both enantiomers have higher affinity when Ca channels are inactivated.