In the present study we have investigated the electrophysiological effects of two prostaglandins, PGI2 (prostacyclin) and PGE1, in ventricular cells enzymatically isolated from adult guinea pigs, using the whole cell patch-clamp technique. PGI2 (tested in the range 1 nM-10 microM) had marked effects on both action potential and calcium current. The action potential duration and the plateau voltage were enhanced, without any significant modification of the other electrical parameters. In this preparation PGI2 increased the calcium current in a concentration-dependent manner, by up to 60% over the control value (at 10 microM), whereas PGE1 (tested in the range 1 nM-10 microM) had practically no effect on the calcium current. Pretreatment with 10 microM acetylcholine markedly reduced the effect of PGI2 (10 microM). No further increase in the calcium current was induced by PGI2 (5 microM) when the cell was internally perfused with 50 microM cAMP. These data indicate that the positive inotropic effect exerted by PGI2 on cardiac preparations is probably due to enhancement in the calcium current via a cAMP-dependent phosphorylation of the calcium channel.