title: Correction of CFTR malfunction and stimulation of Ca-activated Cl channels restore HCO3- secretion in cystic fibrosis bile ductular cells.
abstract: In view of the occurrence of hepatobiliary disorders in cystic fibrosis (CF) this study addresses the role of the cystic fibrosis transmembrane conductance regulator (CFTR) and of Ca(2+)-activated Cl(-) channels in promoting HCO3- secretion in bile ductular cells. Human cholangiocytes were isolated from control livers and from 1 patient with CF (DeltaF508/G542X mutations). Single channel and whole cell currents were analyzed by patch clamp techniques, and HCO3- secretion was determined by fluorometric analysis of the rate of recovery of intracellular pH following alkaline loading. In control cholangiocytes, both cyclic adenosine monophosphate (cAMP) and protein kinase A (PKA) catalytic subunit, activated CFTR Cl(-) channels that exhibited a nonrectifying conductance of 8 pS and appeared in clusters. Activation of Cl(-) current by cAMP was associated with an increase in the rate of HCO3- secretion. The basal rate of HCO3- secretion was lower in CF than in control cholangiocytes. In both control and CF cholangiocytes, raising intracellular Ca(2+) concentrations with ionomycin led to a parallel activation of Cl(-) current and HCO3- secretion. Consistent with reports that premature stop codon mutations (class I; e.g., G542X) can be read over by treatment with aminoglycoside antibiotics, exposure of CF cholangiocytes to gentamicin restored activation by cAMP of Cl(-) current and HCO3- secretion. The observation that activation of Ca(2+)-dependent Cl(-) channels can substitute for cystic fibrosis transmembrane conductance regulator (CFTR) in supporting HCO3- secretion and the efficacy of gentamicin in restoring CFTR function and HCO3- secretion in class I mutations are of potential clinical interest.
authors.affiliation: Department of Pathophysiology, University of Vienna, Vienna, Austria.
authors.forename: Akos
authors.initials: A
authors.lastname: Zsembery
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Jessner
authors.forename: Gerlinde
authors.initials: G
authors.lastname: Sitter
authors.forename: Carlo
authors.initials: C
authors.lastname: Spirlí
authors.forename: Mario
authors.initials: M
authors.lastname: Strazzabosco
authors.forename: Jürg
authors.initials: J
authors.lastname: Graf
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001639:Bicarbonates / Q000378:metabolism*; D001653:Bile Ducts, Intrahepatic / Q000187:drug effects / Q000503:physiopathology*; D002118:Calcium / Q000494:pharmacology*; D002478:Cells, Cultured; D018118:Chloride Channels / Q000187:drug effects / Q000502:physiology*; D003062:Codon; D000242:Cyclic AMP / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000494:pharmacology; D003550:Cystic Fibrosis / Q000503:physiopathology*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics / Q000502:physiology*; D004553:Electric Conductivity; D005839:Gentamicins / Q000494:pharmacology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D015759:Ionomycin / Q000494:pharmacology; D009154:Mutation; D018408:Patch-Clamp Techniques
chemical_list: D000900:Anti-Bacterial Agents; D001639:Bicarbonates; C505032:CFTR protein, human; D018118:Chloride Channels; D003062:Codon; D005839:Gentamicins; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D015759:Ionomycin; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D002118:Calcium