Effect of isoproterenol on the L-type Ca2+ current in cardiac cells from rats and hybernating ground squirrels

The perforated patch clamp method was used to study the effect of the agonist of beta-adrenoreceptors isoproterenol on L-type Ca2+ current in cardiocytes of rats and ground squirrels in two states: active and hibernating. It is shown that isoproterenol exerts a dual effect on Ca2+ currents of rats and ground squirrels in the active state: at Vh = -50 mV, the current increases, whereas at Vh = -30 mV, it decreases. In hibernating ground squirrels, the dual effect of isoproterenol is not observed: isoproterenol increases Ca2+ current at any Vh values. The hypothesis is put forward that, during the entrance of ground squirrels into hibernation, the phosphorylation of one of the sites (not cAMP-dependent) of L-type Ca2+ channels is blocked.