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Query: CAS:6893-26-1 (glutamate)
 73,096 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In the vertebrate retina excitatory transmission seems to be mediated mainly by excitatory amino acids; glutamate and/or aspartate are the most viable candidates to subserve this function. Postsynaptic receptors for N-methyl-D-aspartate (NMDA), kainate (KA), quisqualate (QA) and 2-amino-4-phosphonobutyric acid have been electrophysiologically identified. In this work we have tried to identify and characterize QA receptors through the binding of the most specific analogue available for this receptor: [3H]alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid ([3H]AMPA). AMPA binding to retinal membranes was sodium- and temperature-independent, with optimum pH at 6-7. Ligand-receptor interaction was reversible and saturable. Pharmacologically, glutamate analogues were more active displacers than NMDA analogues: AMPA greater than (RS)-3-hydroxy-4,5,6,7-tetrahydro-isoxazolo-(5,4-C)-pyridine-7-car boxylic acid = L-Glu = QA; with IC50 in the low microM range. Glutamic acid diethylester was uneffective while KA and cis-2,3-piperidine dicarboxylate were potent inhibitors of binding. Binding was stereospecific, L-isomers being more effective displacers than D-forms. Subcellular distribution showed binding concentrated in the inner plexiform layer (IPL), but also present in the outer plexiform layer (OPL). Kinetics of [3H]AMPA binding showed a high affinity kB = 1-2 microM in membranes from complete retina, IPL and OPL, with binding sites concentrated in P2 (Bmax = 16.2 pmol/mg protein). Our results provide biochemical evidence for the presence and distribution of physiologically relevant QA receptors in the chick retina which is in agreement with previous physiological findings.
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PMID:Characterization of quisqualate-type L-glutamate receptors in the retina. 288 40

The binding of [3H]AMPA (DL-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid), a ligand for the putative quisqualate excitatory amino acid receptor subtype, was evaluated using centrifugation and filtration receptor binding techniques in rat brain crude synaptosomal membrane preparations. Maximal specific binding of [3H]AMPA occurred in Triton X-100 treated membranes in the presence of the chaotropic agent potassium thiocyanate (KSCN). The effects of KSCN on binding were reversible and optimal at 100 mM. Supernatant obtained from detergent-treated membranes inhibited specific [3H]AMPA and [3H]kainic acid binding, suggesting the presence of an inhibitory agent which was tentatively identified as glutamate. Using centrifugation, saturation analysis revealed two distinct binding sites in both the absence and presence of KSCN. The chaotrope was most effective in increasing binding at the low affinity binding site, enhancing the affinity (Kd) without a concommitant change in the total number of binding sites. Using filtration, a single binding site was detected in Triton-treated membranes. Like the data obtained by centrifugation, KSCN enhanced the affinity of the receptor (Kd value = 10 nM) without altering the number of binding sites (Bmax = 1.2 pmol/mg protein). The rank order of potency of various glutamate analogs in the [3H]AMPA binding assay was quisqualate greater than AMPA greater than L-glutamate greater than kainate greater than D-glutamate, consistent with the labeling of a quisqualate-type excitatory amino acid receptor subtype. L-glutamic acid diethylester, and 2-amino-7-phosphonoheptanoic acid (AP7) were inactive. The present technique provides a rapid, reliable assay for the evaluation of quisqualate-type excitatory amino acid agonists and/or antagonists that may be used to discover more potent and selective agents.
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PMID:Characterization of quisqualate recognition sites in rat brain tissue using DL-[3H]alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) and a filtration assay. 289 Jan 12

The binding of L-[3H]glutamate to membranes from human temporal cortex was studied in the absence of Na+, Ca2+, and Cl- ions. Pharmacological characterisation revealed that approximately 35% of specific binding at 50 nM L-[3H]glutamate was sensitive to a combination of kainate and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid. The remaining approximately 65% of specific binding was to a single population of sites with a KD of 844 nM and a Bmax of 0.92 pmol/mg protein. The pharmacological characteristics were consistent with an interaction at the N-methyl-D-aspartate subclass of excitatory amino acid receptor. The inclusion of Cl- ions revealed additional glutamate binding; this was sensitive to quisqualate and DL-2-amino-4-phosphonobutyrate, but not to kainate, DL-2-amino-7-phosphonoheptanoate, or alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid.
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PMID:Characterisation of Na+-independent L-[3H]glutamate binding sites in human temporal cortex. 289 29

The appearance, kinetics and pharmacological properties of receptors for n-methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), kainate (KA), L-glutamate (Glu) and L-aspartate (Asp) was investigated using 3H-ligand binding during the development of chick embryo retina. Receptors for AMPA are maximally concentrated at embryonic day 7 (ED 7) and decline 50% in subsequent days; L-Glu receptors are low until ED 11, and the same is true for Asp and NMDA receptors which increase at ED 14 and 18 respectively. All receptors studied underwent an increase in pharmacological specificity, whereas only AMPA-receptors showed an important change in affinity during ontogeny. Results demonstrate that receptors for excitatory amino acids in the retina suffer maturational changes and suggest that while NMDA and aspartate could interact with the same receptor, AMPA and glutamate seem to bind to different sites.
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PMID:Maturational changes in retinal excitatory amino acid receptors. 290 Jun 69

The binding of [3H]alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid ([3H]AMPA), a ligand for the quisqualate subtype of excitatory amino acid receptors, was measured after chemical modifications of rat brain synaptic membranes. Treatment with oxidizing or thiol-alkylating agents did not modify [3H]AMPA binding, whereas treatment with several sulfhydryl reagents produced marked increases in binding. The involvement of free sulfhydryl groups in the regulation of the properties of [3H]AMPA binding sites was suggested by the specificity of p-chloromercuribenzoic acid (PCMB), its sulfonate analog p-chloromercuriphenyl-sulfonic acid (PCMBS), and HgCl2, plus the reversal of their effects after reduction with dithiothreitol. Pretreatment of synaptic membranes with the oxidizing agent 5,5'-dithiobis(2-nitrobenzoic acid) or the alkylating agent N-ethylmaleimide did not significantly affect [3H]AMPA binding but markedly reduced the enhancing effect of PCMBS. On the other hand, the increase in [3H]AMPA binding produced by PCMBS was not prevented by treatment with agonists such as quisqualate or L-glutamate and was produced equally well in resealed postsynaptic membranes with both lipophilic or nonlipophilic SH-reagents. Using filtration assays, two types of binding sites could be detected with high and low affinity for [3H]AMPA. Treatment with SH-reagents produced an increase in the Bmax for the high affinity component and a decrease in the Bmax for the low affinity component, accompanied by an increase in its affinity for the ligand. Using centrifugation assays, the same two types of sites could be detected under control conditions but treatment with SH-reagents produced an increase in affinity of the large component that prevented the analytical differentiation of the two sites. Treatment with SH-reagents also increased the binding of [3H] glutamate to the N-methyl-D-aspartate receptors but did not modify the binding of [3H]kainate to the kainate receptors or the strychnine-insensitive [3H]glycine binding. These results suggest that free sulfhydryl groups allosterically modulate the affinity of the quisqualate subtype of excitatory amino acid receptors and also indicate that different types of glutamate receptors might be differentially affected by chemical modification.
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PMID:Effects of thiol-reagents on [3H]alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid binding to rat telencephalic membranes. 290 Oct 29

1. Intracellular and extracellular recordings were obtained from ganglion cells in the rabbit retina. The effects of glutamate analogues and antagonists were studied using a perfusion method for drug application. 2. Kainate (KA) excited all ganglion cells directly and caused a large increase in firing rate. N-Methyl-DL-aspartate (NMDLA) also excited ganglion cells but it was less potent and caused burst firing. 3. Quisqualate (QQ) and (RS)-2-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA) excited many ganglion cells and were approximately as potent as KA. Less frequently, QQ and AMPA had inhibitory effects possibly due to polysynaptic action. 4. General glutamate antagonists such as cis-2,3-piperidine dicarboxylic acid (PDA) and kynurenic acid blocked the light input to all ganglion cells. PDA and kynurenic acid blocked the effects of KA and NMDLA, but not carbachol, indicating that they act as glutamate antagonists in the rabbit retina. Kynurenic acid did not block the excitatory action of QQ, even though light responses were abolished. 5. Amacrine cells were depolarized by KA or QQ and less potently by NMDLA. Their light-evoked responses were blocked by PDA. 6. We conclude that the light input to ganglion cells in the rabbit retina is predominantly mediated by KA receptors. This is consistent with the idea that 'on' and 'off' bipolar cells are excitatory and release glutamate.
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PMID:Glutamate receptors of ganglion cells in the rabbit retina: evidence for glutamate as a bipolar cell transmitter. 290 48

A series of phosphono and phosphino analogues of glutamate were used to compare the pharmacological properties of (a) Cl-/Ca2+-dependent, 2-amino-4-phosphonobutanoate (AP4)-sensitive L-[3H]-glutamate binding sites in rat brain synaptic plasma membranes (SPMs) and (b) AP4-sensitive excitatory synaptic responses by use of electrophysiological techniques. In the presence of Cl- and Ca2+, L-[3H]-glutamate bound to SPMs with Kd 804 nM and Bmax 53 pmol mg-1 protein. The AP4-sensitive (Ki 7.3 microM) population of binding sites represented 61% of L-glutamate specifically bound. omega-Substituted analogues of AP4 were potent inhibitors of L-[3H]-glutamate binding (Ki values 2.4-38 microM), whereas N-substituted compounds or propionic acid derivatives were inactive. Experiments with AP4 alone and in combination with other analogues demonstrated that the primary target of all substances was the AP4-sensitive population of L-glutamate binding sites. In the hippocampal slice in vitro, AP4 antagonized lateral perforant path-evoked field potentials with an IC50 of 2.7 microM. In contrast to their actions at AP4-sensitive L-glutamate binding sites, all other compounds (except for the omega-carboxymethylphosphino analogue, IC50 19 microM) were weak or inactive as antagonists of this synaptic response (IC50 values greater than 100 microM). Inactive compounds which exhibited activity in the binding assay did not reverse the synaptic depressant effects of AP4, indicating that they were neither agonists nor antagonists at AP4-sensitive synapses. 4 The lack of correspondence between (a) the Cl- /Ca2 -dependent, AP4-sensitive population of L- [3H]-glutamate binding sites and (b) AP4-sensitive synaptic responses indicates that these binding sites are not the receptors through which AP4 exerts its neuropharmacological effects. The possibility that Cl- /Ca2+-dependent 'binding sites' represent transport into resealed SPM vesicles is discussed. 5 Electrophysiological data demonstrate that AP4-sensitive synaptic receptors display a high degree of ligand selectivity. High antagonist potency is shown only by glutamate analogues with unmodified alpha-amino and alpha-carboxyl groups, and with a bifunctional (dianionic) omega-terminal.
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PMID:Cl-/Ca2+-dependent L-glutamate binding sites do not correspond to 2-amino-4-phosphonobutanoate-sensitive excitatory amino acid receptors. 299 27

Glutamate and the glutamate analogue AMPA ((RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid) caused depolarizations of cultured rat spinal and brainstem neurones which were reversibly antagonized by the glutamate antagonist glutamic acid diethylester (GDEE) but not by 2-amino-5-phosphonovalerate (APV), an N-methyl-D-aspartate (NMDA) antagonist. In contrast, depolarizations by NMDA were blocked by APV but not by GDEE. These results suggest that the depolarization by AMPA is caused by the activation of glutamate/quisqualate-preferring receptors.
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PMID:Effects of the glutamate analogue AMPA and its interaction with antagonists on cultured rat spinal and brain stem neurones. 613 61

A biological assay was developed to evaluate rapidly the relative efficacy of marketed and experimental mercurial scavengers. Rat liver mitochondrial protein (1.0 mg) was titrated against methyl-mercuric chloride to the inhibitory level of mitochondrial respiration. Respiration induced by adenosine 5'-diphosphate with succinate (plus rotenone) as the substrate was inhibited consistently by 20.7 +/- 3.9 nmoles of methylmercury/mg of protein. Adenosine 5'-diphosphate-stimulated respiration (State 3) was restored with dimercaprol, penicillamine, and cysteine but not with serine. The antagonists glutathione, 3-mercapto-propionic acid, 2-mercaptoethanol, dithiothreitol, thioglucose, mercaptosuccinic acid, and thiosalicylic acid and mercaptosuccinic acid. Sodium sulfide, thioacetamide, and ethylenediaminetetraacetic acid were completely inactive. Substitution of glutamate (plus malate) for succinate (plus rotenone) as the substrate did not alter the responses significantly. The rat liver mitochondrial assay provides preliminary information about the efficacy and toxicity of water-soluble thiols. Investigations utilizing encapsulated water- and lipid-soluble mercaptans are in progress.
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PMID:New evaluation of potential methylmercury scavengers. 740 Sep 47

1. Inhibitors of extracellular carbonic anhydrase (CAo) offer much promise as diagnostic tools in the study of the synaptic basis of activity-induced alkaline transients in the brain. However, most of the present information related to the effects of CAo blockers in nervous tissue comes from experiments that involve simultaneous synaptic activation of various types of postsynaptic receptor channels. In the present work, double-barreled H(+)-selective microelectrodes were used to study alkaline shifts in extracellular pH (pHo) evoked by selective synaptic and pharmacological activation of glutamate and gamma-aminobutyric acid (GABA) receptors in the CA1 cell body layer in rat hippocampal slices. Inhibition of CAo was achieved with the use of the poorly permeant carbonic anhydrase inhibitor, benzolamide (10 microM; applied in the bath solution) or the impermeant macromolecular inhibitor, prontosil-dextran 5000 (PD 5000; applied in microdrops). 2. Alkaline transients that were exclusively attributable to synaptic activation of glutamate receptors were induced by stimulation of Schaffer collaterals in the presence of picrotoxin (PiTX, 100 microM). An enhancement by the CAo inhibitors of these alkaline transients took place at all stimulus frequencies (5-200 Hz) and stimulus train durations (0.5-20 s) examined. 3. Inhibition of CAo enhanced the alkaline transients evoked by selective synaptic activation of alpha-amino-3-hydroxy-5-methyli-oxazolate- 4-propionic acid (AMPA)/kainate receptors in experiments involving stimulation of Schaffer collaterals in the simultaneous presence of PiTX and D-2-amino-5-phosphonopentoate (AP5, 40-80 microM). 4. Alkaline shifts evoked by selective synaptic activation of N-methyl-D-aspartate (NMDA) receptors were enhanced after inhibition of CAo as seen in experiments where Schaffer collaterals were stimulated in the simultaneous presence of PiTX and 6-cyano-2,3-dihydroxy-7-nitroquinoxaline (CNQX, 20-40 microM) in an Mg(2+)-free solution. 5. Benzolamide and PD 5000 also enhanced the alkaline shifts seen upon pressure injection of glutamate, AMPA, or NMDA. The glutamate-induced alkaline shifts were inhibited by AP5+CNQX, suggesting that uptake of glutamate did not significantly contribute to their generation. 6. Stimuli applied at 5-10 Hz in stratum radiatum close (within 0.5 mm) to the recording site evoked alkaline shifts that were blocked by CNQX plus AP5. In the continuous presence of the two glutamate antagonists, PiTX-sensitive alkaline transients were observed in response to brief high-frequency (20-100 Hz) trains consisting of 100 stimuli. Upon application of pentobarbital sodium (100 microM), these apparently monosynaptically evoked GABAA receptor-mediated alkaline transients were evident also at low stimulation frequencies (5-10 Hz).(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Pharmacological characterization of extracellular pH transients evoked by selective synaptic and exogenous activation of AMPA, NMDA, and GABAA receptors in the rat hippocampal slice. 747 70


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