Liu Q R, López-Corcuera B, Mandiyan S, Nelson H, Nelson N
Roche Institute of Molecular Biology, Roche Research Center, Nutley, New Jersey 07110.
J Biol Chem. 1993 Jan 25;268(3):2106-12.
Two novel gamma-aminobutyric acid (GABA) transporters, GAT3 and GAT4, were cloned from the mouse neonatal brain cDNA library and expressed in Xenopus oocytes. Sequence analysis indicated they were members of the Na(+)-dependent neurotransmitter transporter family. The GABA uptake activities were measured in cRNA injected Xenopus oocytes. The Km for GABA uptake by GAT3 was 18 microM and by GAT4 was 0.8 microM. GAT3 also transports beta-alanine and taurine with Km of 28 and 540 microM, respectively. Similarly, GAT4 transports beta-alanine with Km of 99 microM and taurine with a Km of 1.4 mM. The newly cloned GABA transporters were compared with two previously cloned GABA transporters, GAT1 and GAT2, in terms of molecular and pharmacological properties. While GAT1 and GAT4 gene expression were neural specific, GAT2 and GAT3 mRNAs were detected in other tissues such as liver and kidney, in which GAT3 mRNA was especially abundant. The expression of GAT3 mRNA in mouse brain is developmentally regulated, and its mRNA is abundant in neonatal brain but not in adult brain. High affinity GABA transporters GAT1 and GAT4 were more sensitive to inhibition by nipecotic acid. Low affinity GABA transporters GAT2 and GAT3 were inhibited most effectively by betaine and beta-alanine, respectively. The differential tissue distribution and distinct pharmacological properties of those four GABA transporters suggest functional specialization in the mechanisms of GABA transmission termination.
从新生小鼠脑cDNA文库中克隆出两种新型γ-氨基丁酸（GABA）转运体GAT3和GAT4，并在非洲爪蟾卵母细胞中进行表达。序列分析表明它们是Na⁺依赖性神经递质转运体家族的成员。在注射了cRNA的非洲爪蟾卵母细胞中测定GABA摄取活性。GAT3摄取GABA的Km为18μM，GAT4摄取GABA的Km为0.8μM。GAT3还转运β-丙氨酸和牛磺酸，其Km分别为28μM和540μM。同样，GAT4转运β-丙氨酸的Km为99μM，转运牛磺酸的Km为1.4mM。从分子和药理学特性方面，将新克隆的GABA转运体与之前克隆的两种GABA转运体GAT1和GAT2进行了比较。虽然GAT1和GAT4的基因表达具有神经特异性，但在肝脏和肾脏等其他组织中检测到了GAT2和GAT3的mRNA，其中GAT3的mRNA尤为丰富。GAT3 mRNA在小鼠脑中的表达受发育调控，其mRNA在新生脑中丰富，但在成脑中不丰富。高亲和力GABA转运体GAT1和GAT4对哌啶酸抑制更敏感。低亲和力GABA转运体GAT2和GAT3分别最有效地被甜菜碱和β-丙氨酸抑制。这四种GABA转运体不同的组织分布和独特的药理学特性表明在GABA传递终止机制中存在功能特化。
