COEXPRESSION OF AN ANION CONDUCTANCE PATHWAY WITH NA-GLUCOSE COTRANSPORT IN RAT RENAL BRUSH-BORDER MEMBRANE-VESICLES()

Brush-border membrane vesicles were prepared from superficial rat rena l cortex by a Mg2+-precipitation technique. The initial (20 s) [C-14]g lucose uptake rate from solutions containing 100 mmol/l Na (salt) was found to be dependent upon the anion composition of the medium; in com parison to gluconate-containing medium (0.46 +/- 0.05 nmol/mg protein) , Cl- accelerated the initial rate to 1.47 +/-21 nmol/mg protein (n = 4 preparations, +/- SEM). This enhancement was reduced by -nitro-2-(3- phenylpropylamino)-benzoic acid (NPPB, 0.5 mmol/l), but was unaffected by 4,4'-diisothiocyanatostilbene 2,2'-disulphonate (DIDS, 0.5 mmol/l) . When membrane vesicles were pre-equilibrated with 100 mmol/l K (salt ) and 100 mmol/l mannitol and glucose uptake was measured from a solut ion containing 100 mmol/l Na gluconate and 100 mmol/l mannitol in the presence of 80 mumol/l valinomycin (to generate an outward K+ diffusio n electrical p. d.), it was found that intravesicular KCl depressed th e initial glucose uptake compared to K gluconate. NPPB (0.5 mmol/l) in creased the initial glucose uptake with intravesicular KCl towards val ues seen in K gluconate vesicles. In conditions where the only driving force for glucose uptake was established by an inward anion gradient (Na(o) = Na(i)) it was found that inward Cl- gradients could drive uph ill glucose transport and that this was sensitive to NPPB (0.5 mmol/l) , but insensitive to DIDS. We conclude that a Cl- conductance co-exist s with Na-cotransport in rat renal brush-border membrane vesicles prep ared from superficial renal cortex and this may function to regulate t he activity of electrogenic transport systems at this membrane.