[3H]MK-801 binding sites in post-mortem human frontal cortex.
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.
Kornhuber
J
J
Department of Psychiatry, University of Würzburg, F.R.G.
Mack-Burkhardt
F
F
Kornhuber
M E
ME
Riederer
P
P
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000596:Amino Acids / Q000378:metabolism; D000927:Anticonvulsants / Q000378:metabolism*; D001665:Binding Sites; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism*; D003986:Dibenzocycloheptenes / Q000378:metabolism*; D016291:Dizocilpine Maleate; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D008875:Middle Aged
D000596:Amino Acids; D000927:Anticonvulsants; D003986:Dibenzocycloheptenes; D016291:Dizocilpine Maleate