Acute decrease in net glutamate uptake during energy deprivation.
The extracellular glutamate concentration ([glu](o)) rises during cerebral ischemia, reaching levels capable of inducing delayed neuronal death. The mechanisms underlying this glutamate accumulation remain controversial. We used N-methyl-D-aspartate receptors on CA3 pyramidal neurons as a real-time, on-site, glutamate sensor to identify the source of glutamate release in an in vitro model of ischemia. Using glutamate and L-trans-pyrrolidine-2,4-dicarboxylic acid (tPDC) as substrates and DL-threo-beta-benzyloxyaspartate (TBOA) as an inhibitor of glutamate transporters, we demonstrate that energy deprivation decreases net glutamate uptake within 2-3 min and later promotes reverse glutamate transport. This process accounts for up to 50% of the glutamate accumulation during energy deprivation. Enhanced action potential-independent vesicular release also contributes to the increase in [glu](o), by approximately 50%, but only once glutamate uptake is inhibited. These results indicate that a significant rise in [glu](o) already occurs during the first minutes of energy deprivation and is the consequence of reduced uptake and increased vesicular and nonvesicular release of glutamate.
Jabaudon
D
D
Brain Research Institute, University of Zurich, CH-8057 Zurich, Switzerland.
Scanziani
M
M
Gähwiler
B H
BH
Gerber
U
U
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D018528:ATP-Binding Cassette Transporters / Q000187:drug effects / Q000378:metabolism*; D027322:Amino Acid Transport System X-AG; D000818:Animals; D001224:Aspartic Acid / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002545:Brain Ischemia / Q000503:physiopathology; D003998:Dicarboxylic Acids / Q000493:pharmacokinetics; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000378:metabolism*; D006624:Hippocampus / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D016202:N-Methylaspartate / Q000494:pharmacology; D014179:Neurotransmitter Uptake Inhibitors / Q000493:pharmacokinetics; D009924:Organ Culture Techniques; D018408:Patch-Clamp Techniques; D011759:Pyrrolidines / Q000493:pharmacokinetics; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats
D018528:ATP-Binding Cassette Transporters; D027322:Amino Acid Transport System X-AG; D003998:Dicarboxylic Acids; D018691:Excitatory Amino Acid Antagonists; D014179:Neurotransmitter Uptake Inhibitors; D011759:Pyrrolidines; D011810:Quinoxalines; C120673:benzyloxyaspartate; C062865:2,3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline; D001224:Aspartic Acid; D018698:Glutamic Acid; D016202:N-Methylaspartate; D015763:2-Amino-5-phosphonovalerate; C083486:pyrrolidine-2,4-dicarboxylic acid