INTERDEPENDENCE OF H-PUMPING ACTIVITY OF SARCOPLASMIC-RETICULUM VESICLES( AND K+ FLUXES DURING THE CA2+)

The release of H+ during the oxalate-supported Ca2+ uptake in sarcopla smic reticulum vesicles is kinetically coincident with the initial pha se of Ca2+ accumulation. The Ca2+ uptake is increased and the H+ relea se is decreased in the presence of KCl and other monovalent chloride s alts as expected for a H+-monovalent cation exchange. The functioning of the Ca2+-pump is disturbed by the presence of potassium gluconate a nd, to a lesser extent, of choline chloride. These salts do not inhibi t the ATPase activity of Ca2+-permeable vesicles, suggesting a charge imbalance inhibition which is specially relevant in the case of glucon ate. Therefore, K+, and also Cl-, appear to be involved in secondary f luxes during the active accumulation of Ca2+. The microsomal preparati on seems homogeneous with respect to the K+-channel, showing an appare nt rate constant for K+ release of approximately 25 s-1 measured with the aid of Rb-86+ tracer under equilibrium conditions. A Rb+ efflux, s ensitive to Ca2+-ionophore, can be also detected during the active acc umulation of Ca2+. The experimental data suggest that both monovalent cations and anions are involved in a charge compensation during the Ca 2+ uptake and H+ release. Fluxes of these highly permeable ions would contribute to cancel the formation of a resting membrane potential thr ough the sarcoplasmic reticulum membrane.