Rapid passage of organic anions into human red cells

Abstract

The rates at which organic acids penetrate the human red cell suspended in Tyrode's solution are roughly related to the lipid-to-water partition coefficients of the compounds measured at pH 7.4 using chloroform as a lipidlike solvent. Phenol, sulfadiazine, sulfathiazole, 5-nitrosalicylic acid, p-aminobenzoic acid, and salicylic acid, compounds of relatively high lipid solubility, become equilibrated between the cells and suspending medium in less than 5 min. Phenol red, sulfosalicylic acid, sulfanilic acid, hippuric acid, and p-aminohippuric acid, compounds of lower lipid solubility, become equilibrated more slowly, the times ranging from 1 to more than 7 hr. Measurements of the intracellular binding of phenol red and sulfosalicylic acid indicate that the unbound anions are distributed across the cell membrane according to a Donnan equilibrium. Organic anions enter the cell much more rapidly than do organic cations of a similar low lipid solubility. The preferential permeability toward anions is considered in terms of various models of the cell membrane, and a mechanism for anion penetration is suggested.