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Characterization of the calcium and chloride [3H]glutamate binding site in crude synaptic membranes from human brain
1Unité de Neurobiologie et Pharmacologie (U-109) de l'INSERM, Centre Paul Broca, Paris, France.
Abstract:
1. The specific binding properties of [3H]glutamate to crude synaptic membranes (CSM) from postmortem human brain were studied. 2. Equilibrium binding analysis of [3H]glutamate binding to CSM from human brain cortex revealed a KD = 110 +/- 12 nM and a Bmax = 27 +/- 4 pmol/mg protein). 3. Calcium increased the number of binding sites, Bmax = 44 +/- 6 pmol/mg protein, without a significant change in the affinity constant, KD = 95 +/- 10 nM. 4. The dissociation constant of the [3H]glutamate bound to human CSM was 4.0 +/- 0.4 min-1 (n = 3). 5. The relative potencies of glutamate analogs and 2-amino-4-phosphonobutyric acid (APB) to compete for the glutamate binding sites, in human CSM, were glutamate > quisqualate = ibotenic acid > APB >> alpha-amino-3-hydroxy-5-methyl-4-isoxozolepropionate acid. 6. The glutamate specific binding in CSM from postmortem human brain was particularly rich in the gyrus hippocampus, nucleus accumbens, thalamus and frontal cortex. 7. This glutamate binding protein is related, probably, to a presynaptic neurosecretory pathway.