Permeability of Erythrocytes to Anions and the Regulation of Cell Volume

Abstract

IT is well known that the membrane of red cells is very permeable to Cl⁻ and other anions¹. Tosteson has shown, by making radioisotope measurements, that Cl⁻ enters the red cell in less than 1 s (ref. 2). Theoretical treatments of the mechanism of swelling³ of the red cells have assumed implicitly a high rate of diffusion of anions into the cells. Consequently, the increase in water content has been quantitatively related to diffusion of cations through “leaks” in the membrane. The rate of diffusion of anions through the red cell membrane, however, has never been measured accurately. Because of the restriction of electro-neutrality, as long as the red cell membrane has a low permeability to cations as assumed by the “pump and leak” hypothesis, the experimental conditions used by Tosteson² are suitable for measuring the rate of exchange of anions, but not the rate of net translocation of anions through the red cell membrane. Only when high and specific permeability of the red cell membrane to cations is established can the rate of diffusion of anions through the membrane be determined. Such conditions now seem to be fulfilled by the antibiotic gramicidin which has been reported to render different types of biological membranes and artificial phospholipid bilayers⁵ highly permeable to univalent cations. When gramicidin was first used on red cells, however, the result was unexpected. Chappell and Crofts⁴ reported that addition of gramicidin to a suspension of red cells in isosmotic choline chloride caused efflux of K⁺ and uptake of H⁺ in a 1:1 ratio. If the red cell is highly permeable to Cl⁻, an efflux of Cl⁻ without alkalinization of the medium might be expected. Chappell and Crofts reported no data on the movement of Cl⁻ and water. We report further data on the permeability of the red cell membrane to anions, obtained with the aid of the specificity of gramicidin.