Calcium ion transport by pig erythrocyte membrane vesicles

Abstract

Preincubating pig erythrocyte membranes with ATP enhances their ability to accumulate Ca2+against a concentration gradient. The extent of this increase is dependent on preincubation time over the period 0–60min. As the accessibility of outside membrane markers is decreased by preincubation and as accumulated Ca2+is not removed by EGTA [ethanedioxybis(ethylamine)tetra-acetate], it is suggested that ATP causes the formation of sealed inside-out vesicles which can transport Ca2+inward. The transport system requires ATP and Mg2+and exhibits an apparent dissociation constant for Ca2+of approx. 100μm. Since the dissociation constant for Ca2+-sensitive ATPase (adenosine triphosphatase) in these preparations is similar, it is concluded that this ATPase is responsible for Ca2+transport. Polyphosphoinositide concentrations are also increased during incubation with ATP; however, there is no change in their rate of synthesis or breakdown during Ca2+transport.