VOLUME REGULATION OF NA+ H+ EXCHANGE IN RAT ERYTHROCYTES - EFFECT OF VALINOMYCIN/

We have investigated the activation of Na+/H+ exchange and the regulat ory increase in the volume of rat erythrocytes after the iso- and hype rosmotic, shrinking by, respectively, valinomycin and sucrose. The vol ume was found to restore only after the isoosmotic shrinking and was t otally blocked by amiloride (1 mM). The rate of Na+/H+ exchange in val inomycin-treated erythrocytes was 3-4 times higher than that measured during the shrinking by sucrose. The stimulatory effect of valinomycin was preserved if the cell volume was restored in a hypotonic medium, the carrier was removed by serum albumin and sucrose was used for shri nking. In cells with restored volume we observed a jumpwise increase i n the exchange rate to a maximal level within a narrow range of low su crose concentrations (50 to 100 mM) instead of a smooth increase with the osmolarity of the medium characteristic of native erythrocytes. As judged by the data of flame photometry in valinomycin-treated cells t he concentration of K+ and Cl- was 3 times as low as in native erythro cytes. The role of the intracellular concentration of anions in the vo lume regulation of Na+/H+ exchange is discussed.