Characterization of specific, high-affinity binding sites for L-[3H]glutamic acid in rat brain membranes.
L-[3H]Glutamic acid binds reversibly to rat brain membranes with high affinity. Specific binding is linear with tissue concentration and has a pH optimum at neutrality. Saturation isotherms reveal anomolous kinetics of specific binding with an high affinity site with a KD of 11 nM and a lower affinity site with a KD of 80 nM; the Scatchard plots intercept at a common bound/free ratio. Hill plots of the complete saturation isotherms have a slope of 1.0. There are marked regional differences in the distribution of binding sites in rat brain: parietal cortex, frontal cortex, hippocampus greater than striatum greater than thalamus greater than cerebellum, pons-medulla and hypothalamus. Except for a small amount of specific binding in heart, other peripheral tissues do not exhibit specific binding of L-[3H]glutamic acid. Several amino acids with neuroexcitatory effects inhibit the specific binding: L-glutamic acid greater than L-aspartic acid and D,L-homocysteic acid greater than D-glutamic acid and L-cysteine sulfinic acid; related amino acids without neuroexcitatory effects do not inhibit specific binding. Reputed antagonists of glutamate-induced neuronal depolarization block specific binding: alpha-aminoadipic acid greater than 2-amino,4-phosphonobutyric acid greater than glutamate diethylester. Prior kainate lesion of the neurons intrinsic to the striatum results in a 45% decrement in specific binding of L-[3H]glutamic acid whereas cortical ablation, which causes degeneration of a cortical-striatal glutamatergic projection and reduces striatal glutamate synaptosomal uptake, does not affect specific binding. These results are compatible with the interpretation that the binding of [3H]glutamic acid occurs at excitatory receptors on neurons.
D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D018691:Excitatory Amino Acid Antagonists; D005971:Glutamates / Q000008:administration & dosage / Q000378:metabolism*; D008297:Male; D009434:Neural Pathways / Q000502:physiology; D051381:Rats; D013570:Synaptic Membranes / Q000187:drug effects / Q000378:metabolism*
D018691:Excitatory Amino Acid Antagonists; D005971:Glutamates