Abstracts
1998 Digestive Disease Week

#1044

ANION EXCHANGER AE-2 MEDIATES CHLORIDE TRANSPORT BY GALLBLADDER EPITHELIUM. A. J. Moser, K. Graf, Z. R. Abedin, K. E. Morgenstern, P. R. Smith, J.J. Roslyn, M. Z. Abedin. Dept. of Surgery, Allegheny University of the Health Sciences, and Research Services, Phila VAMC, Philadelphia, PA.

Early gallstone formation is associated with altered Cl- and Na+ transport by prairie dog gallbladder (GB) epithelium. Previous inhibitor studies suggest that gallbladder Cl- transport is mediated by a DIDS-sensitive apical Cl-/HCO3- exchanger. Recent cloning experiments have identified three anion exchanger isoforms (AE-1, AE-2 and AE-3) which are tissue-specific. We hypothesized that AE-2 is expressed by GB epithelium and mediates Cl- transport during gallstone formation. Total RNA was extracted from both prairie dog and human gallbladder epithelia, reverse transcribed, and amplified by PCR using AE-2 specific primers. Molecular cloning and sequence analyses demonstrated the predicted 309 bp PCR products with 92% nucleotide homology between the prairie dog and human AE-2 cDNAs. The deduced 103 amino acid sequences were 97% identical. Subsequent RT-PCR studies of gallbladder epithelium from gallstone patients confirmed the expression of AE-2 by human gallbladder epithelium during gallstone formation. Furthermore, an affinity-purified anti-AE-2 antibody (gift from Dr. S. Alper) specifically identified a ~ 165 kDa polypeptide (in Lane 2; Lane 1: nonimmune serum control) on immunoblots of GB epithelial cell protein obtained from gallstone patients. The Mr of this band corresponds to the known Mr for AE-2. This is the first report of AE-2 expression by human gallbladder epithelium during gallstone formation. Alterations in AE-2 activity may induce abnormal Cl- transport thereby promoting gallstones.

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