The effect of citrate, calcium, and magnesium ions on the potassium movement across the human platelet membrane

The intracellular K+ concentration in platelets is reduced during storage in citrated plasma. As shown previously, pH has a marked influence on this reduction. The effect of citrate and Ca2+ and Mg2+ on the K+ permeability of the membrane and on the active K+ transport across the membrane was investigated. Platelets were incubated in dialyzed plasma at 37 degrees C, pH 5.5 to 7.9, with and without added Ca2+ and Mg2+ and citrate. After 60- to 120-minute incubation, a steady state was reached, and ouabain was added to inhibit the active K+ transport. In the pH interval 5.5 to 6.2 citrate, Ca2+ and Mg2+ had no influence on either the active K+ transport or the K+ permeability. Between pH 7.1 and 7.9, Ca2+ and Mg2+ decreased the permeability, whereas citrate increased it. At pH 7.9, citrate had a depressing effect on the active transport. These results indicate that a low citrate concentration and a pH below 7 are important for maintaining a high intracellular K+ of platelets during storage in plasma.