Effects of calcium deficiency and excess on transmembrane potentials in frog heart.

Abstract : The effects of severe calcium deficiency and calcium excess upon transmembrane potentials in isolated frog ventricular strips have been investigated. Resting potential rose about 5 mv. above normal during perfusion with 3-times-normal calcium and fell about 4 mv. below normal during exposure to calcium-free Clark's solution. Mean overshoot rose about 3 mv. during calcium lack but was unaffected by excess calcium. Maximum depolarization rate increased about 20 percent during calcium deprivation and fell a similar amount during high calcium perfusion; however, the membrane potential at the moment of maximum depolarization rate was unchanged from normal by either experimental solution. High calcium augmented the 'spike' and 'plateau' during repolarization, while calcium deficiency abolished the 'spike,' producing 'hump-backed' action potentials with prolonged membrane reversal. These results are discussed, es5ecially in relation to possible changes in permeability during upstroke of the action potential. (Author)