Functional properties and substrate specificity of the cloned L-glutamate/L-aspartate transporter GLAST-1 from rat brain expressed in Xenopus oocytes.
The rat brain L-glutamate/L-aspartate transporter GLAST-1 is a member of a family of Na(+)-dependent high-affinity L-glutamate transporters proposed to be involved in the termination and modulation of excitatory neurotransmitter signals. Application of electrophysiological and radiotracer techniques on Xenopus oocytes expressing cloned GLAST-1 revealed that the apparent Km value of the transporter for L-glutamate and Na+ ions did not depend on voltage while the maximal transport rate increased with more negative potentials, indicative of a low-field access channel. The apparent Km value of the transporter for L-glutamate depends on the Na+ concentration, suggesting that substrate and ions are transported by GLAST-1 in a simultaneous manner. All of the L-glutamate uptake blockers tested either were substrates or did not affect the current induced by L-glutamate. The changes in the amplitude of the current induced by simultaneous application of two substrates can be interpreted by a competition for one binding site.
Klöckner
U
U
Department of Physiology, Medical Faculty, University of Cologne, Germany.
Storck
T
T
Conradt
M
M
Stoffel
W
W
D027322:Amino Acid Transport System X-AG; D000818:Animals; D001667:Binding, Competitive; D001693:Biological Transport, Active; D001921:Brain / Q000378:metabolism*; D002352:Carrier Proteins / Q000187:drug effects / Q000378:metabolism*; D003001:Cloning, Molecular; D018698:Glutamic Acid / Q000378:metabolism*; D006023:Glycoproteins / Q000187:drug effects / Q000378:metabolism*; D066298:In Vitro Techniques; D007473:Ion Channels / Q000378:metabolism; D008564:Membrane Potentials; D009865:Oocytes / Q000378:metabolism*; D051381:Rats; D012964:Sodium / Q000378:metabolism; D013237:Stereoisomerism; D013379:Substrate Specificity; D014981:Xenopus
D027322:Amino Acid Transport System X-AG; D002352:Carrier Proteins; D006023:Glycoproteins; D007473:Ion Channels; D018698:Glutamic Acid; D012964:Sodium