Chloride channel CLC-3 is expressed by gallbladder epithelium: A potential regulator of Cl− secretion

Abstract

Gallbladder epithelium exhibits uncoupled Na + absorption and CIsecretion in prairie dogs. Prominent gallbladder C1permeability suggests the presence of an unidentified apical CIchannel. In renal tubules, disorders of epithelial transport function such as Dent's disease have been found to originate in altered C1channel function. We have recently found that gallbladder C1secretion is increased prior to cholesterol-induced gallstone formation. The mechanism for gallbladder CIsecretion, however, is not completely understood. Recent molecular cloning experiments have identified two distinct families of chloride channels: the CIC and CLC channels. The CLC family includes several molecular isoforms, CLC0-7, with tissue-specific distribution and function. CLC-2,-3 and -4 are expressed by several tissues, whereas CLC-KI and CLC-5 are highly kidney-specific. We hypothesized that CLC-3 is expressed by gallbladder epithelium and may regulate gallbladder C1transport with important implications in gallstone formation. Total RNA was extracted from both prairie dog and human gallbladder epithelia, reverse transcribed, and amplified by PCR using CLC-3 specific primers. Molecular cloning and sequence analysis demonstrated the predicted 508 bp eDNA with 94% nucleotide homology between prairie dog and human CLC-3 cDNAs. The deduced 168 amino acid sequences were 99% identical. Subsequent RT-PCR analysis confirmed the expression of CLC-3 by the human gallbladder following gallstone formation. This is the first report that CLC-3 is expressed by human gallbladder during gallstone formation. Alterations in CLC-3 activity may alter epithelial CIpermeability and promote gallstones.