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 V_h = −50 mV, the current increases, whereas at V_h = −30 mV, it decreases. In hibernating ground squirrels, the dual effect of isoproterenol is not observed: isoproterenol increases Ca²⁺ current at any V_h 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.