Properties of an anion exchanger in rat renal basolateral membrane vesicles

Sulfate uptake in basolateral membrane vesicles from rat kidney cortexes was studied to test for the presence of an anion exchanger in these membranes. A pH difference (pHout = 6.4, pHin = 8.4) and a sodium gradient (out greater than in, pHout = pHin = 7.4) provided the driving force for intravesicular sulfate accumulation above the equilibrium content ("overshoot"). Sulfate uptake in vesicles preloaded with 25 mM of sulfate, thiosulfate, phosphate, chloride, or bicarbonate, or 10 mM of formate, acetate, L-lactate, pyruvate, p-aminohippurate, or oxalate was stimulated with respect to uptake in unpreloaded vesicles. Probenecid inhibited these trans stimulations. When the uptake of 0.1 mM labeled sulfate was determined in the presence of 5 mM of various anions in the incubation medium, cis inhibitions were observed when sulfate was driven by a proton gradient (out greater than in), a sodium gradient (out greater than in), or a p-aminohippurate gradient (in greater than out). All anions that trans stimulated sulfate uptake also showed a cis inhibition. Only small cis inhibitions were seen with maleate and succinate. No inhibition by any of the anions was found when sulfate uptake was studied in the absence of driving cation or anion gradients. Our data indicate a common exchanger for inorganic and organic anions that can additionally be driven by a sodium gradient and a pH difference. This exchanger may be involved in reabsorption and secretion of anions in the proximal tubule of the rat kidney.