Springer Online Journal Archives 1860-2000
Chemistry and Pharmacology
Abstract The release of H+ during the oxalate-supported Ca2+ uptake in sarcoplasmic reticulum vesicles is kinetically coincident with the initial phase of Ca2+ accumulation. The Ca2+ uptake is increased and the H+ release is decreased in the presence of KCl and other monovalent chloride salts as expected for a H+-monovalent cation exchange. The functioning of the Ca2+-pump is disturbed by the presence of potassium gluconate and, to a lesser extent, of choline chloride. These salts do not inhibit the ATPase activity of Ca2+-permeable vesicles, suggesting a charge imbalance inhibition which is specially relevant in the case of gluconate. Therefore, K+, and also Cl−, appear to be involved in secondary fluxes during the active accumulation of Ca2+. The microsomal preparation seems homogeneous with respect to the K+-channel, showing an apparent rate constant for K+ release of approximately 25 s−1 measured with the aid of86Rb+ tracer under equilibrium conditions. A Rb+ efflux, sensitive to Ca2+-ionophore, can be also detected during the active accumulation of Ca2+. The experimental data suggest that both monovalent cations and anions are involved in a charge compensation during the Ca2+ uptake and H+ release. Fluxes of these highly permeable ions would contribute to cancel the formation of a resting membrane potential through the sarcoplasmic reticulum membrane.
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