The role of glutamate reuptake in regulation of glutamate responses in Aplysia neurons.
Glutamate elicits several different responses on neurons of isolated ganglia of Aplysia, the most common of which is a hyperpolarization due to conductance increases to either chloride or potassium. We have investigated the actions of aspartate and cysteate on the responses to glutamate. Neither aspartate nor cysteate is potent in activation of glutamate receptors. However both aspartate and cysteate cause a dramatic increase in the response to glutamate when ionophoretically applied before the glutamate application. This potentiating effect of aspartate and cysteate is a result of competition with glutamate for the glutamate transport system, since the potentiation is blocked by cooling and by perfusion with sodium-free sea water. Blockade of glutamate re-uptake by perfusion of sodium-free sea water also causes a significant increase in the response to ionophoretically applied glutamate, which in some neurons may be very large. These results demonstrate that the glutamate reuptake system has an important role in regulation of the responses to glutamate which is similar to that of acetylcholinesterase in regulation of responses to acetylcholine. These observations may be of particular importance in mammalian systems where excess glutamate is associated with neuronal excitotoxicity and cell death.
Carpenter
D O
DO
Wadsworth Center for Laboratories and Research, New York State Department of Health and School of Public Health, Albany 12201, USA.
King
W M
WM
McCreery
M J
MJ
D000818:Animals; D001048:Aplysia / Q000187:drug effects / Q000378:metabolism*; D001224:Aspartic Acid / Q000494:pharmacology; D001667:Binding, Competitive; D001693:Biological Transport, Active; D003544:Cysteic Acid / Q000494:pharmacology; D017952:Ganglia, Invertebrate / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism* / Q000494:pharmacology*; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism*; D017470:Receptors, Glutamate / Q000187:drug effects / Q000378:metabolism
D017470:Receptors, Glutamate; D001224:Aspartic Acid; D018698:Glutamic Acid; D003544:Cysteic Acid