Expression of sodium-independent organic anion uptake systems of skate liver in Xenopus laevis oocytes.
The expression of the basolateral sodium-independent organic anion uptake system of the little skate (Raja erinacea) has been studied in Xenopus laevis oocytes. Injection of oocytes with skate liver poly(A)+ RNA resulted in the functional expression of chloride-dependent sulfobromophthalein (BSP) uptake and sodium-independent taurocholate uptake within 3-5 days. The expressed chloride-dependent BSP uptake activity exhibited saturation kinetics [apparent Michaelis constant (Km) 1.8 microM] and efficiently extracted BSP from its binding sites on bovine serum albumin. The chloride-sensitive portion of BSP uptake was inhibited by bilirubin (10 microM; 27%), 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (100 microM; 57%), bumetanide (100 microM; 48%), taurocholate (200 microM; 51%), and cholate (200 microM; 45%). Size fractionation of total skate liver mRNA revealed that a 1.8- to 2.9-kb size class mRNA was sufficient to express chloride-dependent BSP uptake and sodium-independent taurocholate uptake. In addition, a 1- to 1.7-kb size class mRNA expressed sodium-independent taurocholate uptake but had no effects on BSP uptake. This study confirms that an organic anion transport system for chloride-dependent BSP uptake, with characteristics similar to rat liver, is already expressed in the liver of lower vertebrates and thus represents a phylogenetically old system. Sodium-independent taurocholate uptake in skate liver may be mediated by two different transport systems.
Department of Medicine, University Hospital, Zürich, Switzerland.
E
E
Jacquemin
B
B
Hagenbuch
A W
AW
Wolkoff
P J
PJ
Meier
J L
JL
Boyer
D000818:Animals; D027321:Anion Transport Proteins; D000838:Anions / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism*; D005591:Chemical Fractionation; D005260:Female; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism; D012333:RNA, Messenger / Q000494:pharmacology; D012860:Skates, Fish / Q000378:metabolism*; D012964:Sodium / Q000502:physiology*; D013448:Sulfobromophthalein / Q000378:metabolism / Q000493:pharmacokinetics; D013656:Taurocholic Acid / Q000378:metabolism; D014982:Xenopus laevis
D027321:Anion Transport Proteins; D000838:Anions; D002352:Carrier Proteins; D012333:RNA, Messenger; D013448:Sulfobromophthalein; D013656:Taurocholic Acid; D012964:Sodium