Novel Properties of a Mouse c-Aminobutyric Acid Transporter (GAT4)

Abstract. We expressed the mouse c-aminobutyric acid (GABA) transporter GAT4 (homologous to rat/ human GAT-3) in Xenopus laevis oocytes and examined its functional and pharmacological prop-erties by using electrophysiological and tracer uptake methods. In the coupled mode of transport (Na+/ Cl)/GABA cotransport), there was tight coupling between charge flux and GABA flux across the plasma membrane (2 charges/GABA). Transport was highly temperature-dependent with a temperature coefficient (Q10) of 4.3. The GAT4 turnover rate (1.5 s)1;)50 mV, 21C) and temperature dependence suggest physiological turnover rates of 15–20 s)1. No uncoupled current was observed in the presence of Na+. In the absence of external Na+, GAT4 exhib