EXPRESSION OF CYSTIC-FIBROSIS TRANSMEMBRANE CONDUCTANCE REGULATOR IN HUMAN GALLBLADDER EPITHELIAL-CELLS

BACKGROUND: Hepatobiliary complications in cystic fibrosis result pred ominantly from lesions of the biliary epithelium. These abnormalities affect the intrahepatic as well as extrahepatic bile ducts and the gal lbladder. The protein cystic fibrosis transmembrane conductance regula tor (CFTR), the gene product defective in cystic fibrosis, functions a s a cAMP-activated chloride channel in the plasma membrane. As such, i t 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 cel ls and to examine the chloride ion transport properties of these cells . Immunolocalization was performed on tissue sections. The reverse tra nscription-PCR was used to analyze the expression of CFTR mRNA in fres hly isolated and cultured gallbladder epithelial cells. The CFTR prote in was detected by Western blotting and immunoprecipitation. The chlor ide ion transport properties of the cells were determined by Cl-36 eff lux studies. RESULTS: The CFTR protein was immunodetected in human gal lbladder in situ and localized predominantly to the apical membrane of epithelial cells. High levels of CFTR mRNA and protein were maintaine d in gallbladder epithelial cells in primary culture. Glycosylated for ms of CFTR were present as confirmed by treatment with N-glycanase. Ch loride efflux was stimulated by Ca++. dependent pathways but more inte nsely by cAMP-dependent pathways. Stimulation of chloride efflux by ag onists of the cAMP-pathway was inhibited by diphenylamine carboxylic a cid, a chloride channel blocker. Two physiologically active peptides-a cting via cAMP, vasoactive intestinal peptide, and secretin-also stimu lated chloride efflux in vitro. CONCLUSIONS: Our results are consisten t with a high expression of endogenous functional CFTR protein in huma n gallbladder epithelial cells. Physiologically active peptides, vasoa ctive intestinal peptide and secretin, stimulate chloride conductance in these cells. These findings indicate that CFTR plays an important r ole in the pathophysiology of the biliary epithelium, including the ga llbladder epithelium.