SULFATE OXALATE EXCHANGE BY LOBSTER HEPATOPANCREATIC BASOLATERAL MEMBRANE-VESICLES

Purified basolateral membrane vesicles (BLMV) were prepared from lobst er hepatopancreas by osmotic disruption and discontinuous sucrose grad ient centrifugation. Radiolabeled sulfate uptake was stimulated by 10 mM intravesicular oxalate compared with gluconate;loaded vesicles. Sul fate/oxalate exchange was not affected by transmembrane valinomycin-in duced potassium diffusion potentials (inside negative or inside positi ve), suggesting electroneutral anion transport. Sulfate uptake was not stimulated by the similar carboxylic anions formate, succinate, oxalo acetate, or ketoglutarate. Sulfate influx occurred by at least one sat urable Michaelis-Menten carrier system [apparent K-m = 6.0 +/- 1.7 mM; maximum flux (J(max)) = 382.3 +/- 37.0 pmol . mg protein(-1). 7 s(-1) ]. Sulfate/oxalate exchange was significantly reduced by the anion ant iport inhibitors 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid and -acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid but was not af fected by bumetanide or furosemide. The possible physiological role of this exchange mechanism in anion/sulfate transport across the crustac ean hepatopancreas is discussed.