Functional characteristics of l-glutamate, N-methyl-d-aspartate and kainate receptors in isolated brain synaptic membranes

l-Glutamic acid (l-Glu) and other excitatory amino acids and amino acid analogs enhanced [³⁵S]thiocyanate (SCN^-) uptake in isolated-resealed synaptic membrane vesicles. The SCN^- uptake was used as a measure of membrane depolarization to evaluate the characteristics of functional excitatory amino acid receptors in the synaptic membranes. N-Methyl-d-aspartate (NMDA) and l-Glu produced additive effects on SCN^- accumulation indicating the presence of distinct l-Glu and NMDA receptors. On the other hand, kainic acid (KA) and l-Glu shared either common receptor sites or ion channels. The effects of antagonists on NMDA, l-Glu, and KA stimulation of SCN^- influx were consistent with previously reported electrophysiologic observations in intact neurons.