Requirements for high affinity binding of glycine analogs to the glycine site of the NMDA receptor complex

1-Aminocylopropane-1-carboxylic acid derivatives as ligands at the glycine-binding site of the N-methyl-D-aspartate receptor

Several 1-aminocyclopropane-1-carboxylic acid derivatives were prepared and tested for activity at the glycine-binding site of the N-methyl-D-aspartate (NMDA) receptor complex. Structural modifications involved the amino group, the carboxylic function or position 2 of the ring. When tested in a [3H]-MK-801 binding assay in the presence of glutamic acid, some of the compounds were able to activate the receptor. Two of them (3e and 6) are selective ligands for the glycine site of the NMDA receptor.

Characterisation of the binding of [3H]MDL 105,519, a radiolabelled antagonist for the N-methyl-D-aspartate-associated glycine site, to pig cortical brain membranes

Binding of [3H]MDL 105,519 to glycine sites on N-methyl-D-aspartate (NMDA) receptors of pig cortical brain membranes was evaluated. [3H]MDL 105,519 labelled a homogeneous population of binding sites with a Kd-value of 3.73 +/- 0.43 nM and a Bmax-value of 3030 +/- 330 fmol/mg protein. Clear correlations between the affinity (Ki) to [3H]MDL 105,519 labelled sites and the potency (EC50) to enhance or inhibit non-equilibrium [3H]MK-801 binding in the nominal absence of glycine were shown for a variety of glycine site agonists, partial agonists and antagonists. The ratio of Ki to EC50 was >1 for agonists and partial agonists and <1 for antagonists. Various cations as well as glutamate and polyamine site ligands were shown to be able to influence [3H]MDL 105,519 binding to pig cortical brain membranes substantially.

Characterisation of [3H]MK-801 binding and its cooperative modulation by pig brain membranes

Cooperative modulation of [3H]MK-801 binding to extensively washed pig cortical brain membranes in the presence of various concentrations of L-glutamate, glycine, spermine, CPP and DCKA was evaluated in association experiments. In saturation experiments [3H]MK-801 labelled a homogeneous population of binding sites with a Kd-value of 1.26 +/- 0.18 nmol 1(-1) and a Bmax-value of 2130 +/- 200 fmol/mg protein. The pharmacological profile of this site was further evaluated in competition experiments with known NMDA receptor channel blockers. In nonequilibrium binding experiments EC50-values of reference compounds acting at the L-glutamate, at the glycine, and at the polyamine site, were determined by increasing or decreasing [3H]MK-801 binding. Ifenprodil reduced [3H]MK-801 binding in a biphasic manner. All the data obtained are in agreement with results from [3H]MK-801 binding to rodent as well as human brain membranes. This study therefore strongly suggests, that pig cortical membranes are a suitable alternative to rodent brain membranes, and an acceptable substitute for human brain membranes in [3H]MK-801 binding experiments.