Palacin M, Werner A, Dittmer J, Murer H, Biber J
Department of Biochemistry and Physiology, University of Barcelona, Spain.
Biochem J. 1990 Aug 15;270(1):189-95. doi: 10.1042/bj2700189.
Poly(A)+ RNA (mRNA) isolated from rat liver was injected into Xenopus laevis oocytes, and expression of Na+/L-alanine transport was assayed by measuring Na(+)-dependent uptake of L-[3H]alanine. Expression of Na+/L-alanine transport was detected 3-7 days after mRNA injection, and was due to an increment of the Na(+)-dependent component. After injection of 40 ng of total mRNA, Na(+)-dependent uptake of L-alanine was 2.5-fold higher than in water-injected oocytes. In contrast with Na+/L-alanine transport by water-injected oocytes, expressed Na+/L-alanine transport was inhibited by N-methylaminoisobutyric acid, was inhibited by an extracellular pH of 6.5 and was saturated at approx. 1 mM-L-alanine. After sucrose-density-gradient fractionation, highest expression of Na+/L-alanine uptake was observed with mRNA of 1.9-2.5 kb in length. Compared with mRNA isolated from control rats, mRNA isolated from glucagon-treated rats showed a approx. 2-fold higher expression of Na+/L-alanine transport. The results demonstrate that both liver Na+/L-alanine transport systems (A and ASC) can be expressed in X. laevis oocytes. Furthermore, the data obtained with mRNA isolated from glucagon-treated rats suggest that glucagon regulates liver Na+/L-alanine transport (at least in part) via the availability of the corresponding mRNA.
从大鼠肝脏分离的多聚腺苷酸加尾RNA（mRNA）被注射到非洲爪蟾卵母细胞中，通过测量Na⁺依赖性L-[³H]丙氨酸摄取来检测Na⁺/L-丙氨酸转运的表达。在mRNA注射后3 - 7天检测到Na⁺/L-丙氨酸转运的表达，这是由于Na⁺依赖性成分增加所致。注射40 ng总mRNA后，Na⁺依赖性L-丙氨酸摄取比注射水的卵母细胞高2.5倍。与注射水的卵母细胞的Na⁺/L-丙氨酸转运不同，表达的Na⁺/L-丙氨酸转运受到N-甲基氨基异丁酸的抑制，受到细胞外pH 6.5的抑制，并在约1 mM-L-丙氨酸时达到饱和。经过蔗糖密度梯度分级分离后，观察到长度为1.9 - 2.5 kb的mRNA对Na⁺/L-丙氨酸摄取的表达最高。与从对照大鼠分离的mRNA相比，从胰高血糖素处理的大鼠分离的mRNA显示出Na⁺/L-丙氨酸转运的表达约高2倍。结果表明，肝脏的两种Na⁺/L-丙氨酸转运系统（A和ASC）都可以在非洲爪蟾卵母细胞中表达。此外，用从胰高血糖素处理的大鼠分离的mRNA获得的数据表明，胰高血糖素（至少部分地）通过相应mRNA的可用性来调节肝脏Na⁺/L-丙氨酸转运。
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