Abstract
Activation of N-methyl-d-aspartate (NMDA) receptors is known to produce arachidonic acid release, which has been implicated in excitotoxicity. Antagonists and partial agonists at the glycine site of the NMDA receptor, despite exhibiting functional differences in electrophysiological studies, inhibit glutamate-induced neurotoxicity and ischemia-induced neurodegeneration. The objective of this study was to investigate the effects of both glycine site antagonists and partial agonists on NMDA receptor-mediated [3H]arachidonic acid (AA) release evoked by glutamate, NMDA or a competitive inhibitor of the glutamate/aspartate uptake carrier. The [3H]AA release evoked by a maximally effective concentration of glutamate (100 μM) was blocked by the glycine site antagonists 7-chlorokynurenic acid (7-CKYN) and 5,7- dichlorokynurenic acid (5,7-DCKYN) and by a low intrinsic efficacy glycine partial agonist (+)-1-hydroxy-3-aminopyrrolid-2-one [(+)-HA-966]. 1-Aminocyclopropanecarboxylic acid (ACPC), a high intrinsic efficacy glycine partial agonist, did not modify [3H]AA release evoked by 100 μM glutamate. However, ACPC blocked (in a glycine reversible manner) the [3H]AA release induced by NMDA (100 μM) with an IC50 of 131 ± 2 μM. Furthermore,l-trans-pyrrolidine-2,4-dicarboxylate (PDC), a competitive inhibitor of the glutamate transporter, also released [3H]AA (Emax and EC50 of 127 ± 4% and 30 ± 1 μM, respectively). ACPC, 7-CKYN and (±)-2-amino-7-phosphonoheptanoic acid (AP-7), a competitive NMDA receptor antagonist, inhibited [3H]AA release evoked by PDC. These results demonstrate that both glycine site antagonists and partial agonists can inhibit NMDA receptor-mediated [3H]AA release in cerebellar granule cells, an action consistent with the neuroprotective effects of these compounds.
Footnotes
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Send reprint requests to: Ramon Trullas, Ph.D., Unitat de Neurobiologia, IIBB/C.S.I.C., Jordi Girona 18–26, 08034 Barcelona, Spain. E-mail: rtonbi{at}cid.csic.es
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↵1 This work was supported by a grant from Dirección General de Investigación Cientı́fica y Técnica, Ministry of Education of Spain, DGICYT, PB94–0017 to R.T.
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↵2 E.V. was supported by a predoctoral fellowship from Direcció General D’Universitats/CIRIT. Generalitat de Catalunya.
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↵3 A.Z. is a Severo Ochoa Fellow from Ferrer International Foundation.
- Abbreviations:
- AA
- arachidonic acid
- ACPC
- 1-aminocyclopropanecarboxylic acid
- (±)-AP-5
- 2-amino-5-phosphonopentanoic acid
- (±)-AP-7
- 2-amino-7-phosphonoheptanoic acid
- ASP
- aspartate
- BSA
- bovine serum albumin
- 7-CKYN
- 7-chlorokynurenic acid
- 5
- 7-DCKYN, 5,7-dichlorokynurenic acid
- GLU
- glutamate
- GLY
- glycine
- (+)-HA-966
- 1-hydroxy-3-aminopyrrolid-2-one
- HPLC
- high-pressure liquid chromatography
- LH-BSA
- Locke-HEPES buffer with fatty acid-free bovine serum albumin
- MK-801
- 5-methyl-10,11-dihydro-5H-dibenzo(a,d)cyclohept- 5,10-imine hydrogen, dizocilpine maleate
- NMDA
- N-methyl-d-aspartate
- PDC
- l-trans-pyrrolidine-2,4-dicarboxylic acid
- Received October 9, 1997.
- Accepted January 26, 1998.
- The American Society for Pharmacology and Experimental Therapeutics
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