Bilirubin diglucuronide transport by rat liver canalicular membrane vesicles: Stimulation by bicarbonate ion

✍ Scribed by Yukihiko Adachi; Hiroaki Kobayashi; Yoshiaki Kurumi; Mika Shouji; Motokazu Kitano; Toshio Yamamoto

• Book ID: 102853173
• Publisher: John Wiley and Sons
• Year: 1991
• Tongue: English
• Weight: 713 KB
• Volume: 14
• Category: Article
• ISSN: 0270-9139
• DOI: 10.1002/hep.1840140647

✦ Synopsis

The purpose of this study was to provide further insight into the mechanism of bilirubin diglucuronide excretion through the hepatocyte canalicular membrane by investigating the uptake of (SH)bilirubin diglucuronide by purified canalicular membrane vesicles of rat liver. The uptake was analyzed by a rapid filtration technique. The difference between vesicleassociated (=H)bilirubin diglucuronide at 37" C and at 0" C during the initial 1 min was regarded as uptake. Twenty second uptake was saturated by increasing the (,H)bilirubin diglucuronide concentration at a vesicleinside-directed 100 mmoln KCl gradient (K,,, = 75 pmol/L, V, , = 320 pmol/mg protein. 20 sec at 37" C). No sodium dependency was observed. When canalicular membrane vesicles were preincubated with nonlabeled bilirubin diglucuronide, the uptake increased 1.3-fold (transstimulation). Vesicle-insidepositive potential induced by valinomycin and potassium caused a 1.4-fold increase in the uptake. When C1was replaced by equivalent ion concentrations of SO,2-, HC0,-, NO,-and SCN-, the uptake was 78%, 244%, 68% and 50%, respectively, and specific stimulation by HC0,was observed (Eh, = 76 FrnolL, V, , = 700 pmol/mg protein. 20 sec at a vesicle-insidedirected 100 mmol/L KHCO, gradient at 37" C). The uptake was inhibited in a dose-dependent manner by the addition of 4,4'-diisothiocyanatostilbene-2,2'disulfonic acid. The uptake was ATP independent.

From these results, it was concluded that bilirubin d i g l u m n i d e transport through the canalicular membrane is carrier mediated, electrogenic and stimulated