The regulation of L-type Ca2+ currents in rat cardiac myocytes

The perforated patch-clamp technique was used to study the L-type Ca2+ curr ent regulation in isolated rat cardiac cells. It was shown that the effect of cAMP-dependent phosphorylation activator isoproterenol depends on the ho lding potential (V-h). At V-h = -50 mV channel phosphorylation increases th e current, while at V-h = -30 mV it decreases the current. A similar effect was reported previously for the DHP agonist BAY K 8644. At holding potenti als close to the cell resting potential, the effects of BAY K 8644 and isop roterenol are additive. The effect of BAY K 8644 does not depend on protein kinases inhibition by Hg and phosphatases activation by acetylcholine. The results obtained are explained in terms of a new Ca2+ channel model that su ggests the presence of two independent phosphorylation sites.