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

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Abstract
Strychnine-insensitive [3H]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. The ligands invariably potentiated the binding of [3H](+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]-cyclohepten-5,10-imine ([3H]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 [3H]glycine binding. The Triton treatment did not affect the pharmacological profile of [3H]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.