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 Ca2+-activated Cl- channels in promoting HCO3- secretion in bile ductular cells. Human cholangiocytes were isolated from control livers and from 1 patient with CF (ΔF508/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 Ca2+ 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 Ca2+-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.
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