title: Quinolinic acid stimulates synaptosomal glutamate release and inhibits glutamate uptake into astrocytes.
abstract: Quinolinic acid (QA) is an endogenous neurotoxin involved in various neurological diseases, whose action seems to be exerted via glutamatergic receptors. However, the exact mechanism responsible for the neurotoxicity of QA is far from being understood. We have previously reported that QA inhibits vesicular glutamate uptake. In this work, investigating the effects of QA on the glutamatergic system from rat brain, we have demonstrated that QA (from 0.1 to 10mM) had no effect on synaptosomal L-[3H]glutamate uptake. The effect of QA on glutamate release in basal (physiological K+ concentration) or depolarized (40 mM KCl) conditions was evaluated. QA did not alter K+-stimulated glutamate release, but 5 and 10mM QA significantly increased basal glutamate release. The effect of dizolcipine (MK-801), a noncompetitive antagonist of N-methyl-D-aspartate (NMDA) receptor on glutamate release was investigated. MK-801 (5 microM) did not alter glutamate release per se, but completely abolished the QA-induced glutamate release. NMDA (50 microM) also stimulated glutamate release, without altering QA-induced glutamate release, suggesting that QA effects were exerted via NMDA receptors. QA (5 and 10mM) decreased glutamate uptake into astrocyte cell cultures. Enhanced synaptosomal glutamate release, associated with inhibition of glutamate uptake into astrocytes induced by QA could contribute to increase extracellular glutamate concentrations which ultimately lead to overstimulation of the glutamatergic system. These data provide additional evidence that neurotoxicity of QA may be also related to disturbances on the glutamatergic transport system, which could result in the neurological manifestations observed when this organic acid accumulates in the brain.
authors.affiliation: Departamento de Bioquímica, Instituto de Ciências Básicas da Saúde, Universidade Federal do Rio Grande do Sul, Rua Ramiro Barcelos, 2600 (Anexo), 90035-003 Porto Alegre, RS, Brazil.
authors.forename: Rejane G
authors.initials: RG
authors.lastname: Tavares
authors.forename: Carla I
authors.initials: CI
authors.lastname: Tasca
authors.forename: Candice E S
authors.initials: CE
authors.lastname: Santos
authors.forename: Letícia B
authors.initials: LB
authors.lastname: Alves
authors.forename: Lisiane O
authors.initials: LO
authors.lastname: Porciúncula
authors.forename: Tatiana
authors.initials: T
authors.lastname: Emanuelli
authors.forename: Diogo O
authors.initials: DO
authors.lastname: Souza
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D016291:Dizocilpine Maleate / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000378:metabolism*; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D017378:Quinolinic Acid / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism; D013574:Synaptosomes / Q000187:drug effects* / Q000378:metabolism
chemical_list: D018691:Excitatory Amino Acid Antagonists; D016194:Receptors, N-Methyl-D-Aspartate; D018698:Glutamic Acid; D016291:Dizocilpine Maleate; D007770:L-Lactate Dehydrogenase; D017378:Quinolinic Acid