Abstract

The effect of aldosterone on transmembrane potentials of cardiac muscle and pacemaker fibers of the rabbit heart was investigated. It was found that the hormone reduces the polarization of the heart cell membrane and decreases the excitability of atrial muscle. The depolarizing action of the hormone, which appears only after a prolonged exposure (50-60 min), was not observed at 15° C or at 10° C, which suggests that energy-consuming reactions are involved in the mechanism of depolarization. A decrease in heart rate and in the rate of repolarization of the action potentials was also observed. No antagonism between the hormone and acetyicholine on resting membrane potential of atrial muscle fibers was found.