EXPRESSION OR A RAT RENAL SODIUM-DEPENDENT DICARBOXYLATE TRANSPORTER IN XENOPUS-OOCYTES

Microinjection of mRNA isolated from rat kidney cortex into Xenopus la evis oocytes resulted in the expression of a Na+-dependent dicarboxyla te transporter, as detected by uptake measurements with [C-14]succinat e as substrate. The expressed transporter showed an S-shaped Na+-depen dence with half-maximal activation at 19-21 mM Na+ and a Hill coeffici ent between 2 and 3. Endogenous succinate uptake was not Na+-dependent . Na+-stimulated succinate uptake in mRNA-injected oocytes exhibited a maximum at pH 7.5, whereas endogenous Na+-independent transporter was fastest at pH 8.5. The expressed dicarboxylate transporter also diffe red from the endogenous transporter in its sensitivity to citrate as w ell as dicarboxylates in trans and cis configurations. The expressed t ransporter resembled the renal basolateral transporter, especially wit h respect to affinity for succinate (K-m 28 mu M), activation by Na+, pH-dependence and substrate specificity. After injection of size-fract ionated mRNA, succinate uptake was expressed by mRNA of 2-3 kb. Our re sults suggest expression of the basolateral Na+-dependent dicarboxylat e transporter after injection of mRNA from rat kidney into Xenopus ooc ytes.