Determinants of the transmembrane distribution of chloride in rat lymphocytes: role of Cl(-)-HCO3- exchange

Abstract

The purpose of the present experiments was to establish the factors that determine the intracellular Cl- concentration ([Cl-]i) of lymphocytes. Coulometric and isotope equilibration determinations indicated that [Cl-]i was in the range of 70-85 mmol/l cells. Since the membrane potential (Em) of these cells approximates -55 mV, [Cl-]i is severalfold higher than the level expected at electrochemical equilibrium (approximately 16 mM). This suggests that conductive pathways contribute marginally to the distribution of Cl-. Accordingly, altering the force driving conductive Cl- fluxes by manipulating Em had little effect on [Cl-]i. The possible role of electroneutral cation-Cl- cotransport in the accumulation of intracellular Cl- was also assessed. 36Cl- uptake was largely unaffected by omission of extracellular Na+ and K+ or by addition of bumetanide, a potent cotransport inhibitor. Moreover, [Cl-]i remained unaltered for at least 1 h in cells incubated without Na+ or K+ or in the presence of loop diuretics. Thus it appears unlikely that Cl(-)-anion cotransport plays a major role in maintaining [Cl-]i. A vigorous stilbene disulfonate-sensitive anion exchanger was detected in thymocytes. This system constitutes a large fraction of the Cl- flux pathways and is possibly a major contributor to the establishment of [Cl-]i. Accordingly, modifying the force driving Cl- through the exchanger, by altering pH at constant PCO2, resulted in changes in cellular Cl- content and associated changes in cell volume. These effects were markedly reduced in the nominal absence of HCO3- or in the presence of disulfonic stilbene derivatives, suggesting that they are mediated by Cl(-)-HCO3- exchange.(ABSTRACT TRUNCATED AT 250 WORDS)