title: Glutamate release from guinea-pig synaptosomes: stimulation by reuptake-induced depolarization.
abstract: Glutamate (10-100 microM) reversibly depolarizes guinea-pig cerebral cortical synaptosomes. This does not appear to be because of a conventional autoreceptor. Neither kainate at 1 mM, 100 microM N-methyl-D-aspartate (NMDA), 100 microM L-2-amino-4-phosphonobutanoate (APB), nor 100 microM quisqualate affects the Ca2+-dependent release of glutamate from suboptimally depolarized synaptosomes. However, kainate, quisqualate, and the quisqualate agonists beta-N-oxalylamino-L-alanine and alpha-amino-3-hydroxy-5-methylisoxazole propionate cause a slow Ca2+-independent release of glutamate from polarized synaptosomes. However, unlike kainate, quisqualate does not inhibit the acidic amino acid carrier. APB, NMDA, and the NMDA receptor-mediated neurotoxin beta-N-methylamino-L-alanine do not influence Ca2+-independent release at 100 microM. The depolarization of the plasma membrane by glutamate can be mimicked by D-aspartate, can be blocked by the transport inhibitor dihydrokainate, and is accompanied by the net uptake of acidic amino acids. L-Glutamate or D-aspartate at 100 microM increases the cytoplasmic free Ca2+ concentration. D-aspartate at 100 microM causes a Ca2+-dependent release of endogenous glutamate, superimposed on the Ca2+-independent heteroexchange with glutamate through the acidic amino acid carrier. The results suggest that the glutamatergic subpopulation of synaptosomes can be depolarized by exogenous glutamate.
authors.affiliation: Department of Biochemistry, University of Dundee, Scotland.
authors.forename: H T
authors.initials: HT
authors.lastname: McMahon
authors.forename: A P
authors.initials: AP
authors.lastname: Barrie
authors.forename: M
authors.initials: M
authors.lastname: Lowe
authors.forename: D G
authors.initials: DG
authors.lastname: Nicholls
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D015220:Calcium Channels / Q000502:physiology; D002462:Cell Membrane / Q000502:physiology; D002540:Cerebral Cortex / Q000378:metabolism / Q000502:physiology / Q000648:ultrastructure; D004594:Electrophysiology; D005971:Glutamates / Q000378:metabolism* / Q000494:pharmacology; D018698:Glutamic Acid; D006168:Guinea Pigs; D017470:Receptors, Glutamate; D017981:Receptors, Neurotransmitter / Q000502:physiology; D013574:Synaptosomes / Q000378:metabolism* / Q000502:physiology
chemical_list: D000596:Amino Acids; D015220:Calcium Channels; D005971:Glutamates; D017470:Receptors, Glutamate; D017981:Receptors, Neurotransmitter; D018698:Glutamic Acid