Expression of the choroid plexus sodium-nucleoside cotransporter (N3) in Xenopus laevis oocytes

In this study, we determined the expression of the Na(+)-nucleoside cotransporter (N3) in Xenopus laevis oocytes injected with poly(A)+ RNA isolated from rabbit choroid plexus. The Na(+)-dependent thymidine uptake in poly(A)+ RNA-injected oocytes (maximum 4-5 days after injection) increased proportionally with the injected dose of poly(A)+ RNA. Uptake was enhanced 4- to 5-fold in oocytes injected with 40 ng poly (A)+ RNA in comparison to water-injected oocytes. Consistent with the N3 Na(+)-nucleoside cotransporter, Na(+)-dependent thymidine uptake in poly(A)+ RNA-injected oocytes was inhibited significantly by both purine and pyrimidine nucleosides, but not by dideoxycytidine, a nucleoside analog modified on the ribose ring. These data suggest for the first time that the N3 Na(+)-nucleoside cotransporter in rabbit choroid plexus can be expressed in X. laevis oocytes.