[3H]MK-801 labels a site on the N-methyl-D-aspartate receptor channel complex in rat brain membranes.
The potent noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist [3H]MK-801 bound with nanomolar affinity to rat brain membranes in a reversible, saturable, and stereospecific manner. The affinity of [3H]MK-801 was considerably higher in 5 mM Tris-HCl (pH 7.4) than in previous studies using Krebs-Henseleit buffer. [3H]MK-801 labels a homogeneous population of sites in rat cerebral cortical membranes with KD of 6.3 nM and Bmax of 2.37 pmol/mg of protein. This binding was unevenly distributed among brain regions, with hippocampus greater than cortex greater than olfactory bulb = striatum greater than medulla-pons, and the cerebellum failing to show significant binding. Detailed pharmacological characterization indicated [3H]MK-801 binding to a site which was competitively and potently inhibited by known noncompetitive NMDA receptor antagonists, such as phencyclidine, thienylcyclohexylpiperidine (TCP), ketamine, N-allylnormetazocine (SKF 10,047), cyclazocine, and etoxadrol, a specificity similar to sites labelled by [3H]TCP. These sites were distinct from the high-affinity sites labelled by the sigma receptor ligand (+)-[3H]SKF 10,047. [3H]MK-801 binding was allosterically modulated by the endogenous NMDA receptor antagonist Mg2+ and by other active divalent cations. These data suggest that [3H]MK-801 labels a high-affinity site on the NMDA receptor channel complex, distinct from the NMDA recognition site, which is responsible for the blocking action of MK-801 and other noncompetitive NMDA receptor antagonists.
Wong
E H
EH
Merck Sharp and Dohme Research Laboratories, Neuroscience Research Centre, Harlow, Essex, England.
Knight
A R
AR
Woodruff
G N
GN
D000818:Animals; D000927:Anticonvulsants; D001921:Brain / Q000378:metabolism*; D002413:Cations, Divalent; D002462:Cell Membrane / Q000378:metabolism; D002540:Cerebral Cortex / Q000378:metabolism; D003986:Dibenzocycloheptenes / Q000378:metabolism*; D016291:Dizocilpine Maleate; D007700:Kinetics; D008297:Male; D010620:Phenazocine / Q000031:analogs & derivatives / Q000378:metabolism; D010622:Phencyclidine / Q000031:analogs & derivatives / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D016194:Receptors, N-Methyl-D-Aspartate; D017981:Receptors, Neurotransmitter / Q000378:metabolism*; D014018:Tissue Distribution; D014316:Tritium
D000927:Anticonvulsants; D002413:Cations, Divalent; D003986:Dibenzocycloheptenes; D016194:Receptors, N-Methyl-D-Aspartate; D017981:Receptors, Neurotransmitter; D014316:Tritium; D016291:Dizocilpine Maleate; C012134:SK&F 10047; C012058:tenocyclidine; D010620:Phenazocine; D010622:Phencyclidine