Expression of a renal Na+-nucleoside cotransport system (N2) in Xenopus laevis oocytes

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Abstract
Xenopus laevis oocytes have been used for the expression of a renal, pyrimidine-selective, Na+-nucleoside cotransporter (N2). As compared to its uptake in water-injected oocytes, Na+-dependent thymidine uptake was enhanced in a time- and dose- dependent manner in oocytes injected with rat renal cortex total poly(A)+ RNA. An increased uptake was also observed after injection of size fractionated rat renal cortex poly(A)+ RNA (2–3 kb). Consistent with the selectivity of the N2 nucleoside transporter, cytidine significantly inhibited Na+-dependent thymidine uptake in oocytes injected with total poly(A)+ RNA whereas guanosine and formycin B did not. Na+-dependent thymidine uptake was also enhanced in oocytes injected with size fractionated human renal cortex poly(A)+ RNA (2–3 kb). The above data demonstrate functional expression of renal cortex, Na+-nucleoside cotransporters in Xenopus laevis oocytes.