Electrical activity in frog heart after isoproterenol.

The electrical and mechanical activity of myocardial strips from Rana pipiens after injection of isoproterenol (ISO) was studied during cyanide anoxia. Compared to controls, isometric tension was more depressed, resting tension more increased and action potential duration extremely reduced when ISO-damaged heart was exposed to cyanide anoxia. The same results could be obtained after inactivation of the fast Na+-system, when the resting membrane potential was held at -50 mV in elevated Ko+. These alterations are explained by an increase of Cai2+ since cyanide is known to release intracellularly stored Ca2+. Pretreatment with ISO may possibly increase the amount of releasable Ca2+.