Activation of Cl−/OH− exchange by parachloromercuribenzoic acid in rabbit renal brush-border membranes

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Abstract
The effect of the sulfhydryl reagent parachloromercuribenzoic acid (PCMB) on chloride transport was examined in rabbit renal brush-border membrane vesicles (BBMV). PCMB had no effect on the chloride conductive pathway. In the presence of an inside-alkaline pH gradient and a K+/valinomycin voltage clamp, the addition of PCMB stimulated36Cl uptake and induced a threefold overshoot above the equilibrium value, indicating Cl/OH exchange. The effect of PCMB was reversed by dithiothreitol. Cl/OH exchange was not observed in the absence of PCMB. PCMB-activated Cl/OH exchange persisted even when the membrane potential was made inside-negative relative to the controls, thus, demonstrating that PCMB's effect on36Cl uptake under pH-gradient conditions is not mediated by parallel Cl− and H+ conductive pathways. PCMB-activated Cl/OH exchange was inhibited by 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid (DIDS) and 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB) with IC50 values of 290 and 80 μm, respectively. These results demonstrate that modification of sulfhydryl groups by PCMB activates Cl/OH exchange in BBMV.