Expression of Chloride Channel, ClC-5, and Its Role in Receptor-Mediated Endocytosis of Albumin in OK Cells

Abstract

By using Western blot and RT-PCR analyses, the expression of ClC-5, a member of the ClC family of voltage-gated chloride channels, and its mRNA was detected in OK cells. The effect of chloride channel inhibitors on receptor-mediated endocytosis of albumin was examined in OK cells and compared to that of vacuolar H+-ATPase inhibitors. Accumulation of fluorescein-isothiocyanate (FITC)–albumin, a receptor-mediated endocytosis marker, was inhibited by 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB), a chloride channel inhibitor, in a concentration-dependent fashion. In contrast, uptake of FITC–inulin, a fluid-phase endocytosis marker, was not affected by NPPB. Other chloride channel inhibitors, 4,4′-diisothiocyanatostilbene-2-2′-disulfonic acid and diphenylamine-2-carboxylic acid, also inhibited FITC–albumin uptake. NPPB, as well as a vacuolar H+-ATPase inhibitor bafilomycin A1, caused a decrease in the affinity and in the maximal velocity of FITC–albumin uptake. These results suggest that chloride channel, most likely ClC-5, plays an important role in the receptor-mediated endocytosis of albumin in OK cells.