Background: Hepatobiliary complications in cystic fibrosis result predominantly from lesions of the biliary epithelium. These abnormalities affect the intrahepatic as well as extrahepatic bile ducts and the gallbladder. The protein cystic fibrosis transmembrane conductance regulator (CFTR), the gene product defective in cystic fibrosis, functions as a cAMP-activated chloride channel in the plasma membrane. As such, it may represent an important driving force for fluid transport across the epithelium.
Experimental design: The purpose of this study was to investigate the expression of CFTR in human gallbladder epithelial cells and to examine the chloride ion transport properties of these cells. Immunolocalization was performed on tissue sections. The reverse transcription-PCR was used to analyze the expression of CFTR mRNA in freshly isolated and cultured gallbladder epithelial cells. The CFTR protein was detected by Western blotting and immunoprecipitation. The chloride ion transport properties of the cells were determined by 36Cl efflux studies.
Results: The CFTR protein was immunodetected in human gallbladder in situ and localized predominantly to the apical membrane of epithelial cells. High levels of CFTR mRNA and protein were maintained in gallbladder epithelial cells in primary cultured. Glycosylated forms of CFTR were present as confirmed by treatment with N-glycanase. Chloride efflux was stimulated by Ca(++)-dependent pathways but more intensely by cAMP-dependent pathways. Stimulation of chloride efflux by agonist of the cAMP-pathway was inhibited by diphenylamine carboxylic acid, a chloride channel blocker. Two physiologically active peptides--acting via cAMP, vasoactive intestinal peptide, and secretin--also stimulated chloride efflux in vitro.
Conclusions: Our results are consistent with a high expression of endogenous functional CFTR protein in human gallbladder epithelial cells. Physiologically active peptides, vasoactive intestinal peptide and secretin, stimulate chloride conductance in these cells. These findings indicate that CFTR play an important role in the pathophysiology of the biliary epithelium, including the gallbladder epithelium.