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

We have investigated the activation of Na+/H+ exchange and the regulatory increase in the volume of rat erythrocytes after the iso- and hyperosmotic, shrinking by, respectively, valinomycin and sucrose. The volume was found to restore only after the isoosmotic shrinking and was totally blocked by amiloride (1 mM). The rate of Na+/H+ exchange in valinomycin-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 shrinking. In cells with restored volume we observed a jumpwise increase in the exchange rate to a maximal level within a narrow range of low sucrose 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 the concentration of K+ and Cl- was 3 times as low as in native erythrocytes. The role of the intracellular concentration of anions in the volume regulation of Na+/H+ exchange is discussed.