Cloning and characterization of a functional human gamma-aminobutyric acid (GABA) transporter, human GAT-2.
Plasma membrane gamma-aminobutyric acid (GABA) transporters act to terminate GABA neurotransmission in the mammalian brain. Intriguingly four distinct GABA transporters have been cloned from rat and mouse, whereas only three functional homologs of these transporters have been cloned from human. The aim of this study therefore was to search for this fourth missing human transporter. Using a bioinformatics approach, we successfully identified and cloned the full-length cDNA of a so far uncharacterized human GABA transporter (GAT). The predicted protein displays high sequence similarity to rat GAT-2 and mouse GAT3, and in accordance with the nomenclature for rat GABA transporters, we therefore refer to the transporter as human GAT-2. We used electrophysiological and cell-based methods to demonstrate that this protein is a functional transporter of GABA. The transport was saturable and dependent on both Na(+) and Cl(-). Pharmacologically the transporter is distinct from the other human GABA transporters and similar to rat GAT-2 and mouse GAT3 with high sensitivity toward GABA and beta-alanine. Furthermore the GABA transport inhibitor (S)-SNAP-5114 displayed some inhibitory activity at the transporter. Expression analysis by reverse transcription-PCR showed that GAT-2 mRNA is present in human brain, kidney, lung, and testis. The finding of the human GAT-2 demonstrates for the first time that the four plasma membrane GABA transporters identified in several mammalian species are all conserved in human. Furthermore the availability of human GAT-2 enables the use of all human clones of the GABA transporters in drug development programs and functional characterization of novel inhibitors of GABA transport.
Christiansen
Bolette
B
Department of Medicinal Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen, DK-2100 Copenhagen, Denmark.
Meinild
Anne-Kristine
AK
Jensen
Anders A
AA
Braüner-Osborne
Hans
H
D000818:Animals; D000840:Anisoles / Q000494:pharmacology; D001693:Biological Transport, Active / Q000187:drug effects / Q000235:genetics; D002461:Cell Line, Transformed; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D050485:GABA Plasma Membrane Transport Proteins / Q000096:biosynthesis / Q000235:genetics*; D058805:GABA Uptake Inhibitors; D005786:Gene Expression Regulation / Q000187:drug effects / Q000235:genetics; D006801:Humans; D051379:Mice; D009557:Nipecotic Acids / Q000494:pharmacology; D009928:Organ Specificity / Q000187:drug effects / Q000235:genetics; D012333:RNA, Messenger; D051381:Rats; D017386:Sequence Homology, Amino Acid; D012964:Sodium / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
C092337:1-(2-(tris(4-methoxyphenyl)methoxy)ethyl)-3-piperidinecarboxylic acid; D000840:Anisoles; D002712:Chlorides; D018076:DNA, Complementary; D050485:GABA Plasma Membrane Transport Proteins; D058805:GABA Uptake Inhibitors; D009557:Nipecotic Acids; D012333:RNA, Messenger; D005680:gamma-Aminobutyric Acid; D012964:Sodium