Steffgen J, Kienle S, Scheyerl F, Franz H E
Sektion Nephrologie, Universität Ulm, Germany.
Biochem J. 1994 Jan 1;297 ( Pt 1)(Pt 1):35-9. doi: 10.1042/bj2970035.
Microinjection of mRNA isolated from rat kidney cortex into Xenopus laevis oocytes resulted in the expression of a Na(+)-dependent dicarboxylate transporter, as detected by uptake measurements with [14C]succinate as substrate. The expressed transporter showed an S-shaped Na(+)-dependence with half-maximal activation at 19-21 mM Na+ and a Hill coefficient 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 differed from the endogenous transporter in its sensitivity to citrate as well as dicarboxylates in trans and cis configurations. The expressed transporter resembled the renal basolateral transporter, especially with respect to affinity for succinate (Km 28 microM), activation by Na+, pH-dependence and substrate specificity. After injection of size-fractionated mRNA, succinate uptake was expressed by mRNA of 2-3 kb. Our results suggest expression of the basolateral Na(+)-dependent dicarboxylate transporter after injection of mRNA from rat kidney into Xenopus oocytes.
将从大鼠肾皮质分离的mRNA显微注射到非洲爪蟾卵母细胞中，以[14C]琥珀酸为底物进行摄取测量，结果表明表达了一种Na(+)依赖性二羧酸转运体。所表达的转运体表现出S形的Na(+)依赖性，在19 - 21 mM Na+时激活达到半数最大，希尔系数在2到3之间。内源性琥珀酸摄取不依赖于Na(+)。注射mRNA的卵母细胞中，Na(+)刺激的琥珀酸摄取在pH 7.5时达到最大值，而内源性不依赖Na(+)的转运体在pH 8.5时最快。所表达的二羧酸转运体在对柠檬酸盐以及顺式和反式构型的二羧酸盐的敏感性方面也与内源性转运体不同。所表达的转运体类似于肾基底外侧转运体，特别是在对琥珀酸的亲和力（Km 28 microM）、Na(+)激活、pH依赖性和底物特异性方面。注射分级分离的mRNA后，2 - 3 kb的mRNA表达了琥珀酸摄取。我们的结果表明，将大鼠肾脏的mRNA注射到非洲爪蟾卵母细胞后，基底外侧Na(+)依赖性二羧酸转运体得以表达。
