THE EFFECT OF OUABAIN ON CALCIUM IN SUBCELLULAR FRACTIONS OF CARDIAC MUSCLE

¹ Baker Memorial Research Institute, Melbourne, Victorio, Australia

The effects of ouabain on the subceliular distribution of calcium in heart muscle, in which ouabain had been used to provoke a positive inotropic response, and on the calcium-accumulating activity of isolated sarcoplasmic reticulum were investigated. Microsomes prepared from isolated Langendorff-perfused rabbit hearts, in which 10^-7 M ouabain had produced a positive inotropic response, contained less CA⁺⁺ (P < .01) than did microsomes prepared from control hearts perfused without ouabain. Electrical stimulation caused calcium to be displaced from isolated cardiac microsomes. In the presence of L3 mM Ca⁺⁺, this effect of electrical stimulation was enhanced by ouabain, the maximum effect of ouabain being obtained at a concentration of 10^-6 M. In the presence of 2.6 mM Ca⁺⁺, ouabain either enhanced or reversed the effect of electrical stimulation on the displacement of calcium from the microsomal fractions, depending upon the dose of ouabain. In the absence of electrical stimulation, ouabain displaced calcium from isolated microsomes.