Inhibition of N-methyl-D-aspartate evoked sodium flux by MK-801.
The inhibition of N-methyl-D-aspartate (NMDA) stimulated 22Na+ efflux from rat hippocampal slices was studied using competitive and non-competitive receptor antagonists. There was a good correlation between the abilities of the competitive antagonists to block NMDA evoked 22Na+ efflux and their potencies as inhibitors of L-[3H]glutamate binding. The recently reported novel NMDA receptor antagonist, (+)-5-methyl-16,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine (MK-801) was shown to non-competitively inhibit NMDA stimulated 22Na+ efflux with an IC50 value of 0.4 microM. Relatively high (10 microM) concentrations of MK-801 had no effects on quisqualic acid, alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA), or kainic acid stimulated efflux. However, MK-801 was able to block 22Na+ efflux induced by ibotenic acid and L-homocysteic acid, amino acids that act as NMDA receptor agonists. MK-801, (-)-MK-801, and non-competitive NMDA receptor antagonists of the arylcyclohexylamine and dioxolane classes inhibited NMDA stimulated 22Na+ efflux with potencies that reflected their abilities to compete for [3H]MK-801 binding sites in rat cortical membranes. These results indicate the utility of the 22Na+ efflux assay in studying the properties of NMDA receptors and confirm the nature and selectivity of the inhibition of NMDA receptor linked ion channel activation by MK-801.
Ransom
R W
RW
Merck Sharp and Dohme Research Laboratories, West Point, PA 19486.
Stec
N L
NL
D000818:Animals; D000927:Anticonvulsants / Q000494:pharmacology*; D001224:Aspartic Acid / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000494:pharmacology; D003342:Corpus Striatum / Q000187:drug effects / Q000378:metabolism*; D003986:Dibenzocycloheptenes / Q000494:pharmacology*; D016291:Dizocilpine Maleate; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D016202:N-Methylaspartate; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism*
D000927:Anticonvulsants; D003986:Dibenzocycloheptenes; D001224:Aspartic Acid; D016202:N-Methylaspartate; D016291:Dizocilpine Maleate; D012964:Sodium