Neurotransmitter transporters play a major role in achieving low concen-trations of their respective transmitter in the synaptic cleft. The GABA transporter GAT1 belongs to the family of Na + - and Cl – -coupled trans-port proteins which possess 12 putative transmembrane domains and three N-glycosylation sites in the extracellular loop between transmembrane domain 3 and 4.