STUDIES ON THE RADIOCALCIUM UPTAKE AND THE ADENOSINE TRIPHOSPHATASES OF SKELETAL AND CARDIAC SARCOPLASMIC RETICULUM FRACTIONS (SRF)

¹ Imperial Chemical Industries Ltd., Pharmaceuticals Division, Alderley Park, Macclesfield, Cheshire, England

The uptake of Ca⁺⁺ by skeletal and cardiac sarcoplasmic reticulum fractions (SRF) has been studied by centrifugation and ultrafiltration techniques. The Ca⁺⁺-activated adenosine triphosphatase (ATPase) accounted for 45% of the total skeletal, and 20% of the total cardiac, SRF ATPase. Electrical stimulation inhibited the Ca⁺⁺ uptake and the total ATPase of both skeletal and cardiac SRF. The surface active agents, oleate and cetyltrimethylammonium salts (CTA), inhibited the Ca⁺⁺ uptake of both cardiac and skeletal SRF and also the total ATPase of cardiac SRF. The total ATPase of skeletal SRF is stimulated by oleate and by low concentrations of CTA; high concentrations of CTA inhibit the total ATPase. The drugs procaine, cocaine and quinidine slightly stimulated the uptake of Ca⁺⁺ by skeletal SRF; this mechanism is possibly related to their membrane-stabilizing activity. The mobilization of Ca⁺⁺ from cardiac SRF by the alpha blocking agent, phentolamine, may be related to its ability to decrease the contractility of cardiac muscle.

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