Anion permeability and erythrocyte swelling

Permeability of cell membranes to cations may increase as a result of membr ane oxidation or in certain pathologies. We studied the effects of nonselec tive increases in cell membrane permeability to univalent cations on the vo lume of erythrocytes incubated in phosphate-buffered saline (PBS) using amp hotericin B (5-10 mg/l suspension) or gramicidin D (10-100 mug/l suspension ) as the membrane permeabilizing agents. Both antibiotics caused K+ to leak , Na+ to accumulate intracellularly, and cell volume to increase. The inter val needed to reach the equilibrium between the intracellular and extracell ular ion concentrations ranged from 30 min to several hours, depending on t he antibiotic concentration. In spite of a rapid disappearance of cation tr ansmembrane gradients, cell volume increased relatively slow. Even 24 h aft er the membrane permeability was changed, the volume of most erythrocytes d id not increase to the lytic values (about 1.6 times the normal volume). Th e slow increase in erythrocyte volume was accounted for by slow changes in the transmembrane Cl- gradient. 4,4'-Diisothiocyanatostilbene-2,2'-disulfon ic acid (DIDS). a specific inhibitor of anion transport, while producing no effect on the transmembrane Na+ and K+ fluxes induced by the antibiotics, significantly inhibited the decrease in the transmembrane Cl- gradient and the increase in erythrocyte volume. Analysis of these data by means of math ematical modeling showed that it failed to satisfactorily describe the expe rimental kinetics of erythrocyte swelling in response to increases in the m embrane permeability to univalent cations if its permeability to Cl- was se t to be constant. The satisfactory description of this kinetics could be ac hieved by assuming that the membrane permeability to anions decreased with increasing erythrocyte volume. The results obtained demonstrate that transm embrane anion transport may be considered to be a component of the mechanis m responsible for the erythrocyte volume stabilization, because a significa nt decrease in the swelling rate allows the erythrocytes with damaged membr anes to activate a relatively slow (metabolic) mechanisms of cell volume st abilization and/or repair their damaged membranes. (C) 2000 Elsevier Scienc e S.A. All rights reserved.