[3H]MK-801 binding sites in post-mortem human frontal cortex

Eur J Pharmacol. 1989 Mar 29;162(3):483-90. doi: 10.1016/0014-2999(89)90339-7.

Abstract

The binding of [3H]MK-801 ((+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate) was investigated in extensively washed homogenates of post-mortem human frontal cortex. The association of [3H]MK-801 proceeded slowly (t1/2 = 553 min) and reached equilibrium only after a prolonged incubation (greater than 24 h). The dissociation of [3H]MK-801 from the binding site was also slow (t1/2 = 244 min). Glutamate, glycine and magnesium markedly increased the rate of association (t1/2 = 14.8 min) and dissociation (t1/2 = 36.5 min). At equilibrium, the binding was not altered by these substances. Specific binding was linear with protein concentration, was saturable, reversible, stereoselective, heat-labile and was nearly absent in the white matter. Scatchard analysis of the saturation curves obtained at equilibrium indicated that there was a high-affinity (Kd1 1.39 +/- 0.21 nM, Bmax1 0.483 +/- 0.084 pmol/mg protein) and a low-affinity (Kd2 116.25 +/- 50.79 nM, Bmax2 3.251 +/- 0.991 pmol/mg protein) binding site. All competition curves obtained with (+)-MK-801, (-)-MK-801, phencyclidine and ketamine had Hill coefficients of less than unity and were best explained by a two-site model. Thus, our results demonstrate the presence of binding sites for MK-801 in post-mortem human brains and provide evidence for binding site heterogeneity. Furthermore, glutamate, glycine and magnesium accelerate the association and dissociation of [3H]MK-801 to and from its binding sites. The results add support to the hypothesis that MK-801, glutamate, glycine and magnesium all bind to different sites on the NMDA receptor-ion channel complex.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Amino Acids / metabolism
  • Anticonvulsants / metabolism*
  • Binding Sites
  • Cerebral Cortex / drug effects
  • Cerebral Cortex / metabolism*
  • Dibenzocycloheptenes / metabolism*
  • Dizocilpine Maleate
  • Female
  • Humans
  • In Vitro Techniques
  • Male
  • Middle Aged

Substances

  • Amino Acids
  • Anticonvulsants
  • Dibenzocycloheptenes
  • Dizocilpine Maleate