title: Regulation of membrane chloride currents in rat bile duct epithelial cells.
abstract: This study examines the conductive properties of the plasma membrane of cells isolated from the intrahepatic portion of bile ducts. Membrane Cl- conductance was measured in single cells using whole-cell patch clamp recording techniques and in cells in short-term culture using 36Cl and 125I efflux. Separate Ca(2+)- and cAMP-dependent Cl- currents were identified. Ca(2+)-dependent Cl- currents showed outward rectification of the current-voltage relation, time-dependent activation at depolarizing potentials, and reversal near the equilibrium potential for Cl-. Ionomycin (2 microM) increased this current from 357 +/- 72 pA to 1,192 +/- 414 pA (at +80 mV) in 5:7 cells, and stimulated efflux of 125I > 36Cl in 15:15 studies. Ionomycin-stimulated efflux was inhibited by the Cl- channel blocker 4,4'-diisothiocyano-2,2'-stilbene disulfonic acid (DIDS) (150 microM). A separate cAMP-activated Cl- current showed linear current-voltage relations and no time dependence. Forskolin (10 microM) or cpt-cAMP (500 microM) increased this current from 189 +/- 50 pA to 784 +/- 196 pA (at +80 mV) in 11:16 cells, and stimulated efflux of 36Cl > 125I in 16:16 studies. cAMP-stimulated efflux was unaffected by DIDS. Because the cAMP-stimulated Cl- conductance resembles that associated with cystic fibrosis transmembrane conductance regulator (CFTR), a putative Cl- channel protein, the presence of CFTR in rat liver was examined by immunoblot analyses. CFTR was detected as a 150-165-kD protein in specimens with increased numbers of duct cells. Immunoperoxidase staining confirmed localization of CFTR to bile duct cells but not hepatocytes. These findings suggest that Ca(2+)- and cAMP-regulated Cl- channels may participate in control of fluid and electrolyte secretion by intrahepatic bile duct epithelial cells, and that the cAMP-regulated conductance is associated with endogenous expression of CFTR. Abnormal ductular secretion may contribute to the pathogenesis of cholestatic liver disease in cystic fibrosis.
authors.affiliation: Duke University and Veterans Administration Medical Center, Durham, NC 27710.
authors.forename: J G
authors.initials: JG
authors.lastname: Fitz
authors.forename: S
authors.initials: S
authors.lastname: Basavappa
authors.forename: J
authors.initials: J
authors.lastname: McGill
authors.forename: O
authors.initials: O
authors.lastname: Melhus
authors.forename: J A
authors.initials: JA
authors.lastname: Cohn
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001652:Bile Ducts / Q000166:cytology / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D018118:Chloride Channels; D002712:Chlorides / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D003550:Cystic Fibrosis; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D004847:Epithelial Cells; D004848:Epithelium / Q000187:drug effects / Q000502:physiology; D007454:Iodides / Q000378:metabolism*; D015759:Ionomycin / Q000494:pharmacology; D007700:Kinetics; D008099:Liver / Q000737:chemistry / Q000502:physiology*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008565:Membrane Proteins / Q000032:analysis* / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013873:Thionucleotides / Q000494:pharmacology
chemical_list: D018118:Chloride Channels; D002712:Chlorides; D007454:Iodides; D008565:Membrane Proteins; D013873:Thionucleotides; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D005576:Colforsin; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; C015929:8-((4-chlorophenyl)thio)cyclic-3',5'-AMP; D015759:Ionomycin; D000242:Cyclic AMP; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D002118:Calcium