Expression of the hepatocyte Na+/bile acid cotransporter in Xenopus laevis oocytes.
The expression of the basolateral Na+/bile acid (taurocholate) cotransport system of rat hepatocytes has been studied in Xenopus laevis oocytes. Injection of rat liver poly(A)+ RNA into the oocytes resulted in the functional expression of Na+ gradient stimulated taurocholate uptake within 3-5 days. This Na(+)-dependent portion of taurocholate uptake exhibited saturation kinetics (apparent Km approximately 91 microM) and could be inhibited by 4,4'-diisothiocyano-2,2'-disulfonic acid stilbene. Furthermore, the expressed taurocholate transport activity demonstrated similar substrate inhibition and stimulation by low concentrations of bovine serum albumin as the basolateral Na+/bile acid cotransport system previously characterized in intact liver, isolated hepatocytes, and isolated plasma membrane vesicles. Finally, a 1.5- to 3.0-kilobase size-class of mRNA could be identified that was sufficient to express the basolateral Na+/taurocholate uptake system in oocytes. These results demonstrate that "expression cloning" represents a promising approach to ultimately clone the gene and to further characterize the molecular properties of this important hepatocellular membrane transport system.
Hagenbuch
B
B
Department of Medicine, University Hospital, Zurich, Switzerland.
Lübbert
H
H
Stieger
B
B
Meier
P J
PJ
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000235:genetics*; D003001:Cloning, Molecular; D005260:Female; D015870:Gene Expression; D007700:Kinetics; D008099:Liver / Q000032:analysis*; D009865:Oocytes / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D012964:Sodium / Q000494:pharmacology; D013656:Taurocholic Acid / Q000378:metabolism; D014162:Transfection; D014982:Xenopus laevis
D002352:Carrier Proteins; D012333:RNA, Messenger; D013656:Taurocholic Acid; D012964:Sodium