Functional characterization of the human high-affinity choline transporter

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 EC50 values of 2.0 muM, 76 mM, and 48 mM, and with apparent Hill coefficients of 1, 2.5 and 2.3, respectively. (C) 2000 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.