Correction of CFTR malfunction and stimulation of Ca2+-activated Cl− channels restore HCO3 − secretion in cystic fibrosis bile ductular cells

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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 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.
Funding Information
  • Telethon, Italy (E430, E873)
  • MURST (9806210866)
  • MURST (MM06215421)
  • Hungarian (OTKA 29260, FKFP 316, ETT 226/2000)
  • Austria-Hungary (A-8/99)