Abstract
In this study, Xenopus laevis oocytes injected with poly(A) + RNA (mRNA) isolated from human kidney were used to express a Na +-nucleoside cotransporter. Na +-stimulated [ 3H]thymidine uptake was enhanced 2–3-fold in oocytes injected with 50 ng poly(A) + RNA and 4–5-fold in oocytes injected with 20 ng of a size-fractionated human renal cortex mRNA fragment (2–3 kb) in comparison with water-injected oocytes. Na +-dependent thymidine uptake in oocytes injected with the 2–3 kb mRNA fragment was inhibited significantly by thymidine and guanosine but not by formycin B, consistent with the N4 Na +-nucleoside cotransporter. The K m (28 μM) of Na +-dependent thymidine uptake in the oocytes injected with the 2–3 kb mRNA fragment was similar to the K m (27 μM) of Na +-dependent thymidine uptake obtained in human renal brush border membrane vesicles. These data suggest for the first time that a Na +-nucleoside cotransporter from human kidney can be expressed in X. laevis oocytes.
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