AJP - Regulatory, Integrative and Comparative Physiology, Vol 269, Issue 3 572-R577, Copyright © 1995 by American Physiological Society
Sulfate/oxalate exchange by lobster hepatopancreatic basolateral membrane vesicles
G. A. Gerencser, M. A. Cattey and G. A. Ahearn
Department of Physiology, College of Medicine, University of Florida, Gainesville 32610, USA.
Purified basolateral membrane vesicles (BLMV) were prepared from lobster
hepatopancreas by osmotic disruption and discontinuous sucrose gradient
centrifugation. Radiolabeled sulfate uptake was stimulated by 10 mM
intravesicular oxalate compared with gluconate-loaded vesicles.
Sulfate/oxalate exchange was not affected by transmembrane
valinomycin-induced potassium diffusion potentials (inside negative or
inside positive), suggesting electroneutral anion transport. Sulfate uptake
was not stimulated by the similar carboxylic anions formate, succinate,
oxaloacetate, or ketoglutarate. Sulfate influx occurred by at least one
saturable Michaelis-Menten carrier system [apparent Km = 6.0 +/- 1.7 mM;
maximum flux (Jmax) = 382.3 +/- 37.0 pmol.mg protein-1 x 7 s-1].
Sulfate/oxalate exchange was significantly reduced by the anion antiport
inhibitors 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid and
4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid but was not
affected by bumetanide or furosemide. The possible physiological role of
this exchange mechanism in anion/sulfate transport across the crustacean
hepatopancreas is discussed.
