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 agoni st of beta-adrenoreceptors isoproterenol on L-type Ca2+ current in cardiocy tes 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 a nd ground squirrels in the active state: at V-h = -50 mV, the current incre ases, whereas at V-h = -30 mV, it decreases. In hibernating ground squirrel s, the dual effect of isoproterenol is not observed: isoproterenol increase s Ca2+ current at any V-h values. The hypothesis is put forward that, durin g the entrance of ground squirrels into hibernation, the phosphorylation of one of the sites (not cAMP-dependent) of L-type Ca2+ channels is blocked.