[³H]MK‐801 Labels a Site on the N‐Methyl‐D‐Aspartate Receptor Channel Complex in Rat Brain Membranes

Abstract

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.

Cataleptic effects of γ-hydroxybutyrate (GHB) and baclofen in mice: mediation by GABAB receptors, but differential enhancement by N-methyl-d-aspartate (NMDA) receptor antagonists

“…The main finding of this study is that GHB-induced catalepsy was selectively enhanced by dizocilpine, PCP, and ketamine, with a potency order (i.e., dizocilpine > PCP > ketamine, based on their minimum effective dose: 0.178, 3.2, and 17.8 mg/kg, respectively) similar to their relative potencies to antagonize effects of NMDA in vivo (e.g., ) and consistent with their relative affinities at binding sites in the ion channel of the NMDA receptor complex labeled with PCP (e.g., Wong et al 1988) or the PCP derivative, TCP (e.g., Maurice and Vignon 1990). Dizocilpine significantly increased catalepsy when given alone.…”

Acute ammonia toxicity is mediated by the NMDA type of glutamate receptors

“…MK-801 is a potent and selective antagonist of the NMDA type of glutamate receptors which bind to the ion channel of the receptor complex [4,5]. To further confirm that the protective effect of MK-801 is mediated by its action on the NMDA type of glutamate receptors, we assessed the effect of another specific antagonist, AP-5, which acts on a dif'ferent site (the glutamate binding site) of the same receptor.…”

The Increase in TNF-α Levels Is Implicated in NF-κB Activation and Inducible Nitric Oxide Synthase Expression in Brain Cortex after Immobilization Stress

“…injected with BB1101 (a TACE inhibitor; Kupatt et al 1999;Watts et al 1999), with MK-801 ([(ϩ)-5-methyl-10,11-dihydroxy-5H-dibenzo (a,d) cyclohepten-5,10-imine]; dizocilpine), a specific non-competitive NMDA antagonist (Wong et al 1988) or with PDTC (pyrrolidine dithiocarbamate, an inhibitor of the activation of NF-B; Schreck et al 1992). Drugs were administered at the onset of the stress.…”