Characterization of the binding of [3H]-CGS 19755: a novel N-methyl-D-aspartate antagonist with nanomolar affinity in rat brain.
1. CGS 19755 (cis-4-phosphonomethyl-2-piperidine carboxylic acid), a rigid analogue of 2-amino-5-phosphonopentanoic acid (AP5), is one of the most potent competitive N-methyl-D-aspartate (NMDA) antagonists described. Using Triton-treated crude synaptic membranes from rat brain, binding studies indicated that [3H]-CGS 19755 bound with high affinity and selectivity to the NMDA-type excitatory amino acid receptor. 2. [3H]-CGS 19755 binding was saturable, reversible, heat-labile, pH-dependent and linear with protein concentration. Specific binding represented 80-85% of the total amount bound. 3. Using a centrifugation assay, saturation experiments revealed two distinct binding components with Kd values of 9 and 200 nM, and corresponding Bmax values of 0.55 and 1.00 pmol mg-1 protein. In contrast, a single binding component with a Kd value of 24 nM and an apparent Bmax value of 0.74 pmol mg-1 protein was observed with a filtration assay. 4. Competition experiments in which both assay techniques were used, showed that [3H]-CGS 19755 selectively labels the NMDA receptor. The most active inhibitors of [3H]-CGS 19755 binding were L-glutamate and CGS 19755 (IC50 values = 100 nM). 5. In the centrifugation assay, a number of excitatory amino acids were found to generate shallow inhibition curves, and computer analysis indicated the presence of two binding components. The quisqualate receptor ligand AMPA (D,L-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate), kainic acid and the non-competitive NMDA antagonists, such as phencyclidine, tiletamine and MK-801, were without activity. 6. The high affinity binding obtained with [3H]-CGS 19755 by use of filtration techniques thus permits the more rapid evaluation of compounds as potential NMDA antagonists and agonists. Therefore, this rigid analogue of AP5 is a more suitable radioligand for NMDA receptors than [3H]-CPP (34-+/-)2-carboxypiperazin-4-yl)propyl-1-phosphonic acid), the corresponding analogue of 2-amino-7-phosphonoheptanoic acid (AP7).
Murphy
D E
DE
Research Department, CIBA-GEIGY Corporation, Summit, NJ 07901.
Hutchison
A J
AJ
Hurt
S D
SD
Williams
M
M
Sills
M A
MA
D000818:Animals; D001224:Aspartic Acid / Q000031:analogs & derivatives* / Q000378:metabolism; D001921:Brain / Q000378:metabolism*; D007425:Intracellular Membranes / Q000378:metabolism; D008297:Male; D016202:N-Methylaspartate; D010875:Pipecolic Acids; D010880:Piperidines / Q000378:metabolism*; D011869:Radioligand Assay; D051381:Rats; D011919:Rats, Inbred Strains; D016194:Receptors, N-Methyl-D-Aspartate; D017981:Receptors, Neurotransmitter / Q000187:drug effects*
D010875:Pipecolic Acids; D010880:Piperidines; D016194:Receptors, N-Methyl-D-Aspartate; D017981:Receptors, Neurotransmitter; D001224:Aspartic Acid; C053672:selfotel; D016202:N-Methylaspartate