Cl^- channels in basolateral renal medullary membranes XII. Anti-rbClC-Ka antibody blocks MTAL Cl~ channels

Cl^- channels in the med-ullary thick ascending limb (MTAL) studied by either patchclamp technique or reconstitution into lipid bilayers are activated by increases in intracellular Cl^- concentrations. rbClC-Ka, a ClC Cl^- channel, may represent this channel. We therefore evaluated the role of rbClC-Ka in transcellular MTAL Cl^- transport in two separate ways. First, an antibody was raised against a fusion protein containing a 153-amino acid fragment of rbClC-Ka. Immunostaining of rabbit kidney sections with the antibody was localized to basolateral regions of MTAL and cortical thick ascending limb (CTAL) segments and also to the cytoplasm of intercalated cells in the cortical collecting duct. Second, Cl^- uptake and efflux were measured in suspensions of mouse MTAL segments. Cl^- uptake was bumetanide sensitive and was stimulated by treatment with a combination of vasopressin + forskolin + dibutyryl adenosine 3′,5-cyclic monophosphate (DBcAMP). Cl^- efflux was also increased significantly by vasopressin + forskolin + DBcAMP from 114 ± 20 to 196 ± 36 nmol-mg protein^-1·45 s^-1 (P = 0.003). Cr efflux was inhibited by the Cl^- channel blocker diphenylamine-2-carboxylate (154 ± 26 vs. 70 ± 21 nmol-mg protein^-1·45 s^-1, P = 0.003). An antirbClC-Ka antibody, which inhibits the activity of MTAL Cr channels in lipid bilayers, reduced Cl^- efflux from intact MTAL segments (154 ± 28 vs. 53 ± 14 nmol·mg protein^-1-45 s^-1, P = 0.02). These results support the view that rbClC-Ka is the basolateral membrane Cl^- channel that mediates vasopressin-stimulated net Cl^- transport in the MTAL segment.