Kinetic characterization of the phencyclidine-N-methyl-D-aspartate receptor interaction: evidence for a steric blockade of the channel.
The nature of the interactions between the N-methyl-D-aspartate (NMDA) and the phencyclidine (PCP) receptors was studied in membranes obtained from rat cerebral cortex and washed repeatedly to remove endogenous excitatory amino acids. Binding of [3H]-N-[1-(2-thienyl)cyclohexyl]piperidine ([3H]TCP) to its receptor sites in these membranes proceeded slowly and did not reach equilibrium even after incubation for 4 h at 25 degrees C. The dissociation rate of [3H]TCP-receptor complexes was also slow (t1/2 = 128-165 min). Both association and dissociation followed first-order reaction kinetics, with similar time constants (0.0054 min-1). Addition of glutamate and glycine to the washed membranes was immediately followed by a marked increase in the rates of both association of [3H]TCP with the receptors and its dissociation from them (t1/2 = 8 min). Association now followed second-order reaction kinetics. Accelerated association of [3H]TCP with its binding sites could also be induced by NMDA or by glutamate alone, and glycine enhanced the effect. All effects of glutamate and glycine on [3H]TCP binding kinetics were blocked by the competitive NMDA receptor antagonist AP-5 [D-(-)-2-amino-5-phosphovaleric acid]. [3H]TCP-receptor interactions at equilibrium were not altered by AP-5 or by glutamate and glycine. The binding data were fitted to a model in which interactions of [3H]TCP with the receptor involve a two-step process: the outside ligand must cross a barrier (presumably a closed NMDA receptor channel in the absence of agonists). Once agonists are added, this limitation is removed (presumably because the channel is open).(ABSTRACT TRUNCATED AT 250 WORDS)
Kloog
Y
Y
Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, Israel.
Haring
R
R
Sokolovsky
M
M
D000818:Animals; D001224:Aspartic Acid / Q000031:analogs & derivatives* / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002540:Cerebral Cortex / Q000378:metabolism*; D007700:Kinetics; D016202:N-Methylaspartate; D010622:Phencyclidine / Q000378:metabolism*; D051381:Rats; D016194:Receptors, N-Methyl-D-Aspartate; D017981:Receptors, Neurotransmitter / Q000378:metabolism*; D017478:Receptors, Phencyclidine
D016194:Receptors, N-Methyl-D-Aspartate; D017981:Receptors, Neurotransmitter; D017478:Receptors, Phencyclidine; D001224:Aspartic Acid; D016202:N-Methylaspartate; D010622:Phencyclidine