Sustained repression and translocation of Ntcp and expression of Mrp4 for cholestasis after rat 90% partial hepatectomy.

BACKGROUND & AIMS To clarify the mechanism of persistent cholestasis after massive hepatectomy, the relationship between such cholestasis and the expression and localization of organic anion transporters for bile acids was examined in a rat model. METHODS Male Sprague-Dawley rats were subjected to 90% hepatectomy, and tissues were harvested at 0, 1, 3, and 7 days for microarray analysis, quantitative real-time polymerase chain reaction (RT-PCR), Western blotting, and immunohistochemistry to examine the expression of multidrug resistance protein 4 (Mrp4), bile salt export pump (Bsep), and sodium-dependent taurocholate cotransporting polypeptide (Ntcp). RESULTS Persistently elevated levels of serum bile acids were observed at days 3 and 7. RT-PCR and Western blotting indicated that the expression of Mrp4, a bile acid export pump located in the basolateral membrane, was increased at day 3. The expression of Ntcp, a transporter used to uptake bile acids from the sinusoids, was significantly decreased throughout the period. The levels of Bsep, an export pump localized to the canalicular membrane, were unchanged. Immunohistochemistry revealed the localization of Mrp4 and Bsep in the basolateral and canalicular membranes, respectively. On the other hand, at days 3 and 7, Ntcp was localized in the cytoplasm and was hardly detected in the basolateral membrane. CONCLUSIONS These results suggested that the sustained repression and translocation of Ntcp and the expression of Mrp4 at the basolateral membrane seem to be responsible for the high blood bile acids levels after massive hepatectomy.