Cloning of the human homologue of the GABA transporter GAT-3 and identification of a novel inhibitor with selectivity for this site

Molecular cloning has revealed the presence of four high-affinity GABA transporters in the brain. The existence of three of these sites, GAT-2, GAT-3, and BGT-1, was unknown prior to their cloning and almost nothing is known of the role they play in regulating GABAergic transmission. In large measure our paucity of knowledge is attributable to the lack of specific inhibitors for these sites. In the present communication we describe the cloning and expression of the human homologue of GAT-3, and the identification of an inhibitor, (S)-SNAP-5114, with selectivity for this site. (S)-SNAP-5114 displays an IC50 of 5 microM at GAT-3, 21 microM at GAT-2, and > or = 100 microM at GAT-1 and BGT-1. Due to its lipophilicity, (S)-SNAP-5114 is also expected to cross the blood-brain-barrier and therefore, should be an important tool for evaluating the role of GAT-3 in neural function.