EFFECTS OF THE CARDIAC GLYCOSIDES ON THE Ca⁺⁺ UPTAKE OF CARDIAC SARCOPLASMIC RETICULUM

¹ Department of Pharmacology, State University of New York, Downstate Medical Center, Brooklyn, New York

The effect of cardiac glycosides on the Ca⁺⁺ uptake of cardiac sarcoplasmic reticulum fragments was investigated employing the Millipore filtration method. It was found that both ouabain and strophanthin inhibited the Ca⁺⁺ uptake of isolated cardiac sarcoplasmic reticulum fragments, and that the optimal concentration for this inhibitory effect was about 10^-6 M. This inhibitory effect of the cardiac glycosides was more marked in the NaCl medium than in the KCl medium. The determination of the time course of Ca⁺⁺ uptake indicated that the inhibition of Ca⁺⁺ uptake by the cardiac glycosides was most marked at the initial 0.5- to 1-min period of incubation, and became less as the incubation time was prolonged.