Calcium ion transport by pig erythrocyte membrane vesicles Available to Purchase

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.