title: Cl-HCO3 exchange and anion conductance in rat duodenal apical membrane vesicles.
abstract: Transport mechanisms for Cl and HCO3 anions in the apical membrane of rat duodenal enterocytes have been characterized using brush-border membrane vesicles. 36Cl uptake was stimulated by outwardly directed gradients of OH, HCO3, and Cl anions. The anion exchanger was sensitive to inhibition by 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) (Ki, 1.3 mmol/l), 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), and furosemide. The process was electroneutral, since voltage clamping the membrane potential to 0 mV or applying a large inside-positive potential had no effect on the magnitude of uptake. The kinetic properties of the exchanger were measured and an apparent Km of 9.8 mM Cl and a Vmax of 134 nmol.mg protein-1.4 s-1 were found. In addition, an electrogenic conductive component of 36Cl uptake was found. This component was dependent on an inside-positive membrane potential and was inhibited by the Cl channel blocker diphenylamine-2-carboxylate. SITS, DIDS, and furosemide had no effect on the electrogenic component of 36Cl uptake. An apparent anion selectivity of SCN greater than I greater than Br greater than Cl greater than HCO3 greater than SO4 greater than Glu greater than PO4 was found. These results support the presence of both Cl-HCO3 exchange and a conductive anion channel in the apical membrane of rat duodenal enterocytes.
authors: Department of Medicine, Hope Hospital, University of Manchester School of Medicine, Salford, United Kingdom.
authors: C D
authors: CD
authors: Brown
authors: C R
authors: CR
authors: Dunk
authors: L A
authors: LA
authors: Turnberg
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000494:pharmacology; D000818:Animals; D000838:Anions; D001639:Bicarbonates / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides / Q000378:metabolism*; D004386:Duodenum / Q000502:physiology*; D005665:Furosemide / Q000494:pharmacology; D007413:Intestinal Mucosa / Q000502:physiology*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D008871:Microvilli / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000502:physiology*; D051381:Rats
chemical_list: D000838:Anions; D001639:Bicarbonates; D002352:Carrier Proteins; D027963:Chloride-Bicarbonate Antiporters; D002712:Chlorides; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D005665:Furosemide; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid