EFFECT OF IONS ON SARCOPLASMIC RETICULUM FRAGMENTS

Fragments of cardiac sarcoplasmic reticulum (FSR) were prepared from homogenates of dog hearts and skeletal FSR from rabbit white skeletal muscle by differential centrifugation. The effect of substituting NO3-, I-, and SCN- for Cl on the ATPase and Ca uptake of fragmented dog cardiac sarcoplasmic reticulum (grana) was studied. Calcium uptake and ATPase were depressed in the order SCN- > I- > N03-, the sequence found for skeletal FSR (2). The effects of the divalent cations Zn2+ and UO22+ were studied on both rabbit white skeletal muscle and dog cardiac FSR; 1 mm Zn2+ and uranyl depressed calcium uptake of both preparations. The results are discussed in terms of the effects of these ions on cardiac and skeletal muscle contraction and current views of excitation-contraction coupling. © 1968.