E. Jacquemin et al., EXPRESSION OF SODIUM-INDEPENDENT ORGANIC ANION UPTAKE SYSTEMS OF SKATE LIVER IN XENOPUS-LAEVIS OOCYTES, American journal of physiology: Gastrointestinal and liver physiology, 31(1), 1995, pp. 18-23
The expression of the basolateral sodium-independent organic anion upt
ake system of the little skate (Raja erinacea) has been studied in Xen
opus laevis oocytes. Injection of oocytes with skate liver poly(A)(+)
RNA resulted in the functional expression of chloride-dependent sulfob
romophthalein (BSP) uptake and sodium-independent taurocholate uptake
within 3-5 days. The expressed chloride-dependent BSP uptake activity
exhibited saturation kinetics [apparent Michaelis constant (K-m) 1.8 m
u M] and efficiently extracted BSP from its binding sites on bovine se
rum albumin. The chloride-sensitive portion of BSP uptake was inhibite
d by bilirubin (10 mu M; 27%), 4,4'-diisothiocyanostilbene-2,2'-disulf
onic acid (100 mu M; 57%), bumetanide (100 mu M; 48%), taurocholate (2
00 mu M; 51%), and cholate (200 mu M; 45%). Size fractionation of tota
l 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-indepen
dent 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 syste
m for chloride-dependent BSP uptake, with characteristics similar to r
at liver, is already expressed in the liver of lower vertebrates and t
hus represents a phylogenetically old system. Sodium-independent tauro
cholate uptake in skate liver may be mediated by two different transpo
rt systems.