Molecular cloning and functional characterization of a GABA/betaine transporter from human kidney.

The human homologue of the canine GABA/betaine transporter (BGT-1) was isolated from a kidney inner medulla cDNA library. The coding sequence predicts a 614 amino acids protein with the typical features of neurotransmitter transporter family. The gene maps to chromosome 12p13 and, in addition to kidney, is also expressed in brain, liver, heart, skeletal muscle, and placenta. Functional studies reveal a Km = 20 microM for GABA transport and a coupling to Na+ and Cl- with a stoichiometry 3 Na+:2 Cl-:1 GABA. At 500 microM the GABA transport was inhibited by various compounds with the following potency order: quinidine > verapamil > phloretin > betaine.