title: Electroneutral uptake and electrogenic secretion of a fluorescent bile salt by rat hepatocyte couplets.
abstract: The role of membrane voltage as a driving force for the hepatic uptake and secretion of fluorescent bile salts has been examined in isolated hepatocyte couplets. The present study demonstrates that the fluorescent bile salt derivative (N-[7-(nitrobenz-2-oxa- 1,3-diazol-4-yl)]-7-amino-3 alpha, 12 alpha-dihydroxy-5-cholan-24-oyl)-2-aminoethanesulfonate (7 beta-NBD-NCT) is taken up into hepatocytes by a saturable process with a Kt of 2.7 microM. Uptake rate was reduced by only 22% after total Na+ replacement and was independent of transmembrane potential difference over a range of -135 to +25 mV. In contrast, secretion into the canalicular space was strongly dependent on membrane voltage over the range from -34 to 0 mV in a manner consistent with electrodiffusion of an anion. Fitting the secretion time course to that predicted by electrodiffusion demonstrated that only approximately 50% of total secretion can result from electrodiffusion. Studies in isolated perfused liver confirmed this observation that depolarization caused a decrease in bile salt secretion rate. These results demonstrate that 7 beta-NBD-NCT is transported by a neutral uptake process at the sinusoidal membrane and is secreted across the canalicular membrane in part by electrogenic transport. This suggests that voltage changes could be a common pathway resulting in impaired organic anion secretion in diverse cholestatic syndromes.
authors.affiliation: Department of Medicine and Liver Center, Yale University School of Medicine, New Haven, Connecticut 06514.
authors.forename: S A
authors.initials: SA
authors.lastname: Weinman
authors.forename: J
authors.initials: J
authors.lastname: Graf
authors.forename: C
authors.initials: C
authors.lastname: Veith
authors.forename: J L
authors.initials: JL
authors.lastname: Boyer
mesh_terms: D000818:Animals; D001647:Bile Acids and Salts / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D004563:Electrochemistry; D004594:Electrophysiology; D007477:Ions; D008099:Liver / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D008856:Microscopy, Fluorescence; D010069:Oxadiazoles / Q000493:pharmacokinetics*; D010477:Perfusion; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D013654:Taurine / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D013656:Taurocholic Acid / Q000378:metabolism / Q000031:analogs & derivatives
chemical_list: D001647:Bile Acids and Salts; D007477:Ions; D010069:Oxadiazoles; C079985:(N-(7-(nitrobenz-2-oxa-1,3-diazol-4-yl))-7-amino-3alpha,12alpha-dihydroxycholan-24-oyl)-2-aminoethanesulfonate; D013654:Taurine; D013656:Taurocholic Acid; D011188:Potassium