Mechanism of Cl- transport in eel intestinal brush-border membrane vesicles

Cl- transport was studied in a preparation of brush-border membrane vesicles (BBMV) from seawater eel intestine. 36Cl- uptake appeared to be stimulated by a positive inside membrane diffusion potential generated (a) by a concentration gradient of salts, the cations of which are more permeable than the anions, (b) by a K+ diffusion potential obtained by imposing a K+ concentration gradient (Cout greater than Cin) in the presence of valinomycin, (c) an inwardly directed H+ ion concentration gradient. The membrane-potential-driven Cl- transport was inhibited by 1 mM 5-nitro-2-(4-phenylpropyl-amino)-benzoic acid. Arachidonic acid also inhibited Cl- uptake in eel intestinal BBMV, but the effect appeared to be unspecific, as the unsaturated fatty acid also affected the Na+ dependent D-glucose uptake. The effect of arachidonic acid was reversed in the presence of bovine serum albumin. Cl- influx was the same in the presence of inwardly directed gradients of Li+, Na+ or K+, arguing against the presence of Na(+)-Cl-, as well as K(+)-Cl- cotransport. The absence of a significant contribution of the Na(+)-K(+)-2Cl- cotransport mechanism to the Cl- uptake in seawater eel intestinal BBMV was indicated from the observations that Cl- uptake was not stimulated by the simultaneous presence of inwardly directed Na+ and K+ gradients, and that it was nearly insensitive to 1 mM bumetanide in the presence of extravesicular Na+ and K+. Furthermore, no evidence for the dependence of Cl- uptake on the Na+ gradient was obtained under a short-circuited membrane diffusion potential, i.e. in the presence of equilibrated K+ and valinomycin.