Okuda T, Haga T
Department of Neurochemistry, Faculty of Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, 113-0033, Tokyo, Japan.
FEBS Lett. 2000 Nov 3;484(2):92-7. doi: 10.1016/s0014-5793(00)02134-7.
Na(+)-dependent, high-affinity choline uptake in cholinergic neurons is the rate-limiting step in acetylcholine synthesis. Here we report the molecular cloning and functional characterization of the human high-affinity choline transporter (hCHT1). The hCHT1 exhibits significant homology with known members of the Na(+)-dependent glucose transporter family, but not with members of the neurotransmitter transporter family. The human CHT1 gene is 25 kb in length with 9 exons and was assigned to chromosome II at position IIq11-12. Northern blot analysis showed that a 5.4 kb hCHT1 transcript was expressed exclusively in tissues containing cholinergic neurons. When expressed in Xenopus oocytes, the human clone induced Na(+)- and Cl(-)-dependent, high-affinity choline uptake, which was sensitive to the specific inhibitor hemicholinium-3, with a K(i) of 1.3 nM. The hCHT1-mediated choline uptake increased with increasing concentrations of choline, Na(+) and Cl(-), with EC(50) values of 2.0 microM, 76 mM, and 48 mM, and with apparent Hill coefficients of 1, 2.5 and 2.3, respectively.
胆碱能神经元中依赖钠离子的高亲和力胆碱摄取是乙酰胆碱合成的限速步骤。在此，我们报告人类高亲和力胆碱转运体（hCHT1）的分子克隆及功能特性。hCHT1与已知的依赖钠离子的葡萄糖转运体家族成员具有显著同源性，但与神经递质转运体家族成员无同源性。人类CHT1基因长度为25 kb，含9个外显子，定位于染色体11上的11q11 - 12位置。Northern印迹分析显示，一个5.4 kb的hCHT1转录本仅在含有胆碱能神经元的组织中表达。当在非洲爪蟾卵母细胞中表达时，人类克隆体诱导出依赖钠离子和氯离子的高亲和力胆碱摄取，该摄取对特异性抑制剂半胱氨酸3敏感，抑制常数（K(i)）为1.3 nM。hCHT1介导的胆碱摄取随胆碱、钠离子和氯离子浓度增加而增加，其半数有效浓度（EC(50)）值分别为2.0 μM、76 mM和48 mM，表观希尔系数分别为1、2.5和2.3。
