CFTR mediates electrogenic chloride secretion in mouse inner medullary collecting duct (mIMCD-K2) cells

Previously we demonstrated that the inner medullary collecting duct cell line mIMCD-K2 secretes Cl^- by an electrogenic mechanism [N. L. Kizer, B. Lewis, and B. A. Stanton. Am. J. Physiol. 268 (Renal Fluid Electrolyte Physiol. 37): F347-F355, 1995; N. L. Kizer, D. Vandorpe, B. Lewis, B. Bunting, J. Russell, and B. A. Stanton. Am. J. Physiol. 268 (Renal Fluid Electrolyte Physiol. 37): F854-F861, 1995]. The goal of the present study was to characterize the Cl^- channel responsible for adenosine 3',5'-cyclic monophosphate (cAMP)stimulated Cl^- secretion. To this end, using the patch- clamp technique, we measured Cl^- currents. In whole cell patch-clamp experiments, 8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphate (CPT- cAMP) activated Cl^- currents that were time and voltage independent, inhibited by diphenylamine 2-carboxylate (DPC), and had a linear current- voltage (I-V) relation. In cell-attached patches of the apical membrane, we identified 7-pS Cl^- channels that were stimulated by CPT-cAMP. In inside- out patches with Cl^- in the pipette and bath solutions, Cl^- currents had a linear I-V relation. The halide permeability sequence was P(Cl) = P(Br) > P(I). The Cl^--channel inhibitors DPC, 5-nitro-2-(3-phenylpropylamino)- benzoic acid, and glibenclamide blocked the 7-pS Cl^- channel, whereas 4,4'- diisothiocyanostilbene-2,2'-disulfonic acid was ineffective. By reverse transcriptase polymerase chain reaction, we isolated a partial cDNA clone encoding the cystic fibrosis transmembrane conductance regulator in mIMCD-K2 cells. We conclude that cAMP stimulates electrogenic Cl^- secretion in inner medullary collecting duct cells by activating cystic fibrosis transmembrane conductance regulator Cl^- channels.