Activation of glutamate receptors stimulates the formation of nitrite in synaptosomes from rat cerebellum.

Abstract

Synaptosomes from rat cerebellum were used to investigate the involvement of different glutamate receptor subtypes in the control of the synthesis of nitric oxide (NO), measured as its breakdown product nitrite (NO2-). Synaptosomes incubated in the presence of NADPH and L-arginine produced measurable levels of NO2-, which were reduced by addition of N omega-nitro-L-arginine methyl ester, an inhibitor of nitric oxide synthase. The selective ionotropic glutamate receptor agonist N-methyl-D-aspartate (NMDA) induced a pronounced increase in NO2- formation, which was prevented by N omega-nitro-L-arginine methyl ester and by the specific NMDA receptor antagonist DL-2-amino-5-phosphonovaleric acid (AP-5). The NMDA-induced increase in NO2- formation was blocked by chelation of extracellular Ca2+ with EGTA. Both L-glutamate and the selective agonist for the metabotropic glutamate receptors (+/-)-1-aminocyclopentane-trans-1,3-dicarboxylic acid raised NO2- production, which returned to control levels after addition of N omega-nitro-L-arginine methyl ester. The selective glutamate ionotropic receptor agonist (R,S)-alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid did not cause any change in NO2- formation. The stimulatory effect of L-glutamate was blocked by the metabotropic glutamate receptor antagonist DL-2-amino-4-phosphonobutyric acid but was unaffected by the selective NMDA receptor blocker AP-5. Removal of extracellular Ca2+ by EGTA did not affect the action of L-glutamate; whereas W-7, an inhibitor of calmodulin, and dantrolene, a compound that blocks the mobilization of Ca2+ from intracellular stores, abolished the effect of L-glutamate on NO2- formation.(ABSTRACT TRUNCATED AT 250 WORDS)