Interaction of Strychnine‐Insensitive Glycine Binding with MK‐801 Binding in Brain Synaptic Membranes

Strychnine‐insensitive [ 3 H]glycine binding was detected in brain synaptic membranes treated with Triton X‐100 using a filtration assay method. The binding was a time‐dependent, inversely temperature‐dependent, and reversible process with a relatively high affinity for the neuroactive amino acid. Scatchard analysis revealed that Triton treatment doubled both the affinity and density of the binding sites, which consisted of a single component. The binding was not only displaced by structurally‐related amino acids such as D‐serine and D‐alanine, but also inhibited by some peptides containing glycine, including glycine methylester and N ‐methylglycine. These ligands invariably potentiated the binding of [ 3 H](+)‐5‐methyl‐10,11‐dihydro‐5 H ‐dibenzo[ a,d ]‐cyclohepten‐5,10‐imine ([ 3 H]MK‐801), a noncompetitive antagonist for the N ‐methyl‐D‐aspartate‐sensitive subclass of the central excitatory amino acid receptors, in a concentration‐dependent manner. Among various endogenous tryptophan metabolites, kynurenic acid significantly inhibited the strychnine‐insensitive [ 3 H]glycine binding. The Triton treatment did not affect the pharmacological profile of [ 3 H]MK‐801 binding sites. These results suggest that brain synaptic membranes treated with Triton X‐100 are useful in evaluating the strychnine‐insensitive and kynurenate‐sensitive binding sites of glycine, which are functionally linked to N ‐methyl‐D‐aspartate‐sensitive receptor channels.