EXPRESSION OF THE CHOROID-PLEXUS SODIUM-NUCLEOSIDE COTRANSPORTER (N3)IN XENOPUS-LAEVIS OOCYTES

In this study, we determined the expression of the Na+-nucleoside cotr ansporter (N3) in Xenopus laevis oocytes injected with poly(A)(+) RNA isolated from rabbit choroid plexus. The Na+-dependent thymidine uptak e in poly(A)+ RNA-injected oocytes (maximum 4-5 days after injection) increased proportionally with the injected dose of poly(A)+ RNA, Uptak e 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 anal og 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.