Evidence for carrier mediated transport of conjugated bile acids across the basolateral membrane of biliary epithelial cells: a study in intrahepatic bile ductules isolated from rat liver. Benedetti, A., A. Di Sario, L. Marucci, G. Svegliati-Baroni, C. D. Schteingart, H. T. Ton-Nu, and A. F. Hofmann. Department of Gastroenterology and Institute of Experimental Pathology, University of Ancona, School of Medicine, Ancona, Italy and Department of Medicine, University of California, School of Medicine, San Diego, La Jolla, CA, 92093-0813
APStracts 3:0273G, 1996.
When secreted into bile, unconjugated dihydroxy- bile acids are absorbed passively by cholangiocytes according to the cholehepatic circulation hypothesis. A fraction of these is likely to be conjugated during transcellular transport. Experiments were performed using fluorescent conjugated bile acids to test whether carrier mediated transport of conjugated bile acids is present in the basolateral domains of polarized cholangiocytes of intrahepatic bile ductules isolated from rat liver. The time course of the cellular localization of cholyl-NBDAB-gly and chenodeoxycholyl-NBDAB-gly, which are anionic fluorescent derivatives of the corresponding glycine conjugated bile acids, was characterized using an image analysis system. With 0.3-3 [mu]M solutions, fluorescence was present at 1 and 3 minutes in the basolateral area of cholangiocytes. Staining in the apical region occurred later, with a peak after 15 min of incubation. The basolateral uptake of the two fluorescent bile acids was temperature-dependent, was Na+ independent, and was not influenced by the addition of amiloride, or by lowering of the medium pH to 6.0, or by preincubation with valinomycin. Uptake was partially inhibited by the absence of Cl- or HCO3- in the perfusate, by preincubation with DIDS, and by the presence of different organic anions or unconjugated and conjugated bile acids in the medium. When cells were preloaded with an ethyl ester of chenodeoxycholyl-NBDAB -gly, which is hydrolyzed by intracellular esterases, the decrease of cell fluorescence was partly inhibited by H2DIDS, while it was stimulated by the presence of 20 [mu]M cholyl taurine in the medium. It is concluded that transport of conjugated bile acid anions across the basolateral membrane of the polarized rat cholangiocyte is carrier mediated. The conjugated bile acid transporter is likely to be an anion exchanger and to be involved in bile secretion whenever conjugated bile acids or other organic anions are transported from the base of the biliary ductular epithelial cells into the plasma of the periductular capillary plexus. 

Received 10 June 1996; accepted in final form 23 November 1996.
APS Manuscript Number G232-6.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996