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[ 3 H]MK‐801 Labels a Site on the N ‐Methyl‐D‐Aspartate Receptor Channel Complex in Rat Brain Membranes
Author(s) -
Wong Erik H. F.,
Knight Antony R.,
Woodruff Geoffrey N.
Publication year - 1988
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1988.tb13260.x
Subject(s) - nmda receptor , phencyclidine , dizocilpine , chemistry , binding site , dextrorphan , receptor , population , biophysics , allosteric regulation , stereochemistry , biochemistry , biology , demography , sociology
The potent noncompetitive N ‐methyl‐D‐aspartate (NMDA) receptor antagonist [ 3 H]MK‐801 bound with nanomolar affinity to rat brain membranes in a reversible, saturable, and stereospecific manner. The affinity of [ 3 H]‐MK‐801 was considerably higher in 5 m M Tris‐HCl (pH 7.4) than in previous studies using Krebs‐Henseleit buffer. [ 3 H]MK‐801 labels a homogenous population of sites in rat cerebral cortical membranes with K D of 6.3 n M and B max of 2.37 pmol/mg of protein. This binding was unevenly distributed among brain regions, with hippocampus > cortex > olfactory bulb = striatum > medulla‐pons, and the cerebellum failing to show significant binding. Detailed pharmacological characterization indicated [ 3 H]HIMK‐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 [ 3 H]TCP. These sites were distinct from the high‐affinity sites labelled by the σ receptor ligand (+)‐[ 3 H]SKF 10,047. [ 3 H]MK‐801 binding was allosterically modulated by the endogenous NMDA receptor antagonist Mg 2+ and by other active divalent cations. These data suggest that [ 3 H]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.