EXPRESSION OF A NON-MDR2-CODED LIVER PHOSPHATIDYLCHOLINE MEMBRANE-TRANSPORT PROTEIN IN XENOPUS-LAEVIS OOCYTES

Phosphatidylcholines (PC) are secreted into the bile via a membrane tr ansport protein(s). Recently, evidence for ATP-dependent mdr2-encoded PC transport as well as for carrier-mediated PC transport had been rep orted. Therefore, we investigated whether mdr2 P-glycoprotein is invol ved in the transport of a water-soluble short chain phosphatidylcholin e analogue L-alpha-dibutyroyl-PC (diC(4)PC) induced by expression of l iver mRNA in Xenopus laevis oocytes. Expression of mouse and rat mdr2 cRNA did not result in diC(4)PC net uptake in Xenopus laevis oocytes. By contrast oocytes showed a similar carrier-mediated uptake activity for diC(4)PC after injection of mouse, rat and human liver total mRNA (Km 7.7, 9.6, and 11.6 mM). Antisense inhibition of mdr2 mRNA expressi on increased diC(4)PC uptake induced by total liver mRNA from mouse an d rat. The present data prove the existence of a specific mRNA for a n on-mdr2-coded cell membrane PC carrier in mouse, rat, and human liver which exhibits similar transport affinity for diC(4)PC as the PC carri er in rat liver canalicular membranes. (C) 1997 Academic Press.