Kinetics of a human glutamate transporter

• Published in: Neuron (Cambridge, Mass.) Vol. 14; no. 5; pp. 1019 - 1027
• Main Authors: Wadiche, Jacques I, Arriza, Jeffrey L, Amara, Susan G, Kavanaugh, Michael P
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.05.1995
• Subjects: Amino Acid Transport System X-AG; Animals; ATP-Binding Cassette Transporters - genetics; ATP-Binding Cassette Transporters - physiology; Brain Chemistry; Cloning, Molecular; Electric Conductivity; Female; Gene Expression; Gene Transfer Techniques; Humans; Kainic Acid - pharmacology; Kinetics; Membrane Potentials; Motor Cortex - chemistry; Oocytes - metabolism; Xenopus
• ISSN: 0896-6273; 1097-4199
• DOI: 10.1016/0896-6273(95)90340-2

Currents mediated by a glutamate transporter cloned from human motor cortex were measured in Xenopus oocytes. In the absence of glutamate, voltage jumps induced Na+-dependent capacitive currents that were blocked by kainate, a competitive transport antagonist. The pre-steady-state currents can be described by an ordered binding model in which a voltage-dependent Na+–binding is followed by a voltage-independent kainate binding. At -80 mV, two charges are translocated per molecule of glutamate, with a cycling time of approximately 70 ms, which is significantly slower than the predicted time course of synaptically released glutamate. The results suggest that glutamate diffusion and binding to transporters, rather than uptake, are likely to dominate the synaptic concentration decay kinetics.