Paradoxical temperature dependence of Na and K fluxes in human red cells

1. The effect of temperature on passive movements of sodium and potassium through the red cell membrane has been determined in the presence of various monovalent anions. 2. Passive sodium and potassium fluxes varied in a complex way with temperature, when the isotonic electrolyte media contained 120 m M thiocyanate or salicylate. Between 0 and 18° C the fluxes decreased with increasing temperature. Above 18° C the rate of permeation increased when temperature was increased. 3. The ability of anions to induce an increased sodium influx at 0° C was gradually intensified through the following sequence of anions:HCO 3 - < Cl - = Br - < NO 3 - < I - « SCN - « salicylate. 4. It is proposed that the anion induced effects on the cation permeability are secondary to binding of anions to fixed cations in the red cell membrane. The temperature dependence of the cation fluxes is assumed to reflect the binding on anions to fixed charges at temperatures between 0 and 18° C.