On the regulation of NMDA receptors by nitric oxide.
Nitric oxide (NO) is generated in central synapses on activation of N-methyl-D-aspartate (NMDA) receptors and exerts physiological effects by changing cGMP levels. NO has frequently also been claimed to engage a different mechanism, namely the covalent modification of thiol residues (S-nitrosation), and thereby exert a negative feedback on NMDA receptors. Tests of this hypothesis were conducted by recording NMDA receptor-mediated synaptic potentials in the CA1 area of rat hippocampal slices. Manipulations designed to increase or decrease endogenous NO levels had no effect. Addition of exogenous NO using a NONOate donor in concentrations up to 30-fold higher than those needed to evoke maximal cGMP accumulation also had no effect. Nevertheless, in agreement with previous findings, photolysis of a caged NO derivative with UV light led to an enduring block of synaptic NMDA receptors. To address these contradictory results, NMDA receptor-mediated currents were recorded from HEK-293 cells transfected with NR1 and NR2A subunits. As found in slices, photolysis of caged NO inhibited the currents whereas perfusion of NO (up to 5 microM) was ineffective. However, when NO was supplied at a concentration found to be effective when released photolytically (5 microM) and the cells simultaneously exposed to the UV light used for photolysis, NMDA receptor-mediated currents were inhibited. This effect was not observed at more physiological NO concentrations (10 nM range). The results indicate that neither endogenous NO nor exogenous NO in supra-physiological concentration inhibits synaptic NMDA receptors; the combination of high NO concentration and UV light can give an artifactual result.
Hopper
Rachel
R
Wolfson Institute for Biomedical Research, University College London, Cruciform Building, Gower Street, London WC1E 6BT, United Kingdom.
Lancaster
Barrie
B
Garthwaite
John
J
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D002460:Cell Line; D006152:Cyclic GMP / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004594:Electrophysiology / Q000379:methods; D004622:Embryo, Mammalian; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D018698:Glutamic Acid / Q000494:pharmacology; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D006834:Hydrazines / Q000494:pharmacology; D066298:In Vitro Techniques; D007668:Kidney; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism*; D020030:Nitric Oxide Donors / Q000494:pharmacology; D009589:Nitrogen Oxides; D010782:Photolysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D013482:Superoxide Dismutase / Q000494:pharmacology; D014162:Transfection / Q000379:methods; D014527:Uric Acid / Q000494:pharmacology
D018691:Excitatory Amino Acid Antagonists; D006834:Hydrazines; D020030:Nitric Oxide Donors; D009589:Nitrogen Oxides; D016194:Receptors, N-Methyl-D-Aspartate; D014527:Uric Acid; D009569:Nitric Oxide; D018698:Glutamic Acid; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D015763:2-Amino-5-phosphonovalerate; C084012:1,1-diethyl-2-hydroxy-2-nitrosohydrazine; D013482:Superoxide Dismutase; D006152:Cyclic GMP