Organic phosphates modulate anion self-exchange across the human erythrocyte membrane

Abstract

Anion transport across the red cell membrane has been measured as sulfate self-exchange flux J a in fresh and metabolically depleted human red cells. Depletion of metabolic stores by a starvation of the cells decreases J a by 50%. A similar effect was observed when ATP was acutely and selectively depleted by iodoacetamide. This inhibition was independent of the presence of calcium and reversible after metabolic rejuvenation of the cells. Ghosts prepared from fresh red cells exhibited the same value of J a as fresh red cells. By contrast, ghosts prepared from depleted red cells exhibited a decrease in J a which was reverted by a physiological concentration of ATP. The effect of ATP was dependent on its concentration ( K m ≈ 40 μM) and on the duration of the metabolic depletion: complete restoration of J a was obtained only in ghosts prepared from red cells acutely depleted of ATP by a 2 h incubation with iodoacetamide. After a 20 h starvation, J a restoration was never more than 80%. We postulate that ATP acts primarily through the phosphorylation of band 3 protein, the anion exchanger; it acts also through the stabilization of the normal organization of the membrane. This latter effect may involve the phosphorylation of membrane components, but also a direct interaction, as shown by the influence of other organic phosphates (2,3-diphosphoglycerate and inositol hexaphosphate) on J a in the absence of ATP.