Sulfate transport by chick renal tubule brush-border and basolateral membranes

Abstract

Brush-border and basolateral membrane vesicles (BBMV and BLMV, respectively) were prepared from chick kidney by a calcium precipitation method and by centrifugation on an 8% Percoll self-generating gradient, respectively. In BBMV a 100-mM Na gluconate gradient, out greater than in, caused concentrative sulfate uptake approximately fivefold greater at 1 min than at 60 min (equilibrium) whether or not the membranes were short-circuited with 100 mM K gluconate, in = out, plus 20 micrograms valinomycin/mg protein. A 48-mM HCO3- gradient, in greater than out, stimulated a 2.5-fold higher uptake at 1 min than at 60 min, and short circuiting as above had no effect on the magnitude of this response. Imposition of a H+ gradient (pH 5.4 out vs. pH 7.4 in) caused concentrative uptake fourfold higher at 1 min than at equilibrium. Short circuiting as above or addition of 0.1 mM carbonyl cyanide m-chlorophenylhydrazone (CCCP) significantly inhibited the pH gradient effect. Creation of an inside positive electrical potential with 100 mM K gluconate, out greater than in, plus valinomycin, also caused concentrative sulfate uptake. The K gradient in the absence of valinomycin had no effect on sulfate uptake (compared with isosmotic mannitol). Based on inhibitor/competitor effects, these are distinct sulfate transport processes. In chick BLMV, imposition of an HCO3- gradient, in greater than out, produced concentrative sulfate uptake; however, neither Na+ nor H+ gradients had significant effects at 15 s. 4-Acetamido-4'-isothiocyanostilbene 2,2'-disulfonic acid disodium at 0.1 mM was an effective inhibitor of BLMV bicarbonate-sulfate exchange; however, neither Cl-, SCN-, nor CCCP inhibited.