共查询到20条相似文献,搜索用时 187 毫秒
1.
Jin-Wuk Han Michiko Nakamura† In-Sun Choi† Jin-Hwa Cho† Hye-Mi Park† Maan-Gee Lee‡§ Byung-Ju Choi† Hyun-Jung Jang Il-Sung Jang†§ 《Journal of neurochemistry》2009,109(4):995-1007
Although it has been well established that GABAA receptors are molecular targets of a variety of allosteric modulators, such as benzodiazepines, the pharmacological properties of presynaptic GABAA receptors are poorly understood. In this study, the effects of diazepam and Zn2+ on presynaptic GABAA receptors have been investigated by measuring the GABAA receptor-mediated facilitation of spontaneous glutamate release in mechanically dissociated rat CA3 pyramidal neurons. Diazepam significantly enhanced the muscimol-induced facilitation (particularly at submicromolar concentrations) of spontaneous glutamate release and shifted the concentration–response relationship for muscimol toward the left, whereas Zn2+ (≤ 100 μM) had little effect on the muscimol-induced facilitation of spontaneous glutamate release. In contrast, Zn2+ significantly suppressed the muscimol-induced currents mediated by GABAA receptors expressed on dentate gyrus granule cells, which are parent neurons of mossy fibers, whereas the effect of diazepam on GABAA receptors expressed on dentate gyrus granule cells was lesser than that on presynaptic GABAA receptors. The results suggest that the pharmacological properties of GABAA receptors differ considerably between presynaptic (axon terminals) and somatic regions in the same granule cell and that presynaptic GABAA receptors should be considered as one of the important pharmacological targets of many drugs affecting GABAA receptors. 相似文献
2.
Rapid Down-Regulation of GABAA Receptors in the Gerbil Hippocampus Following Transient Cerebral Ischemia 总被引:1,自引:1,他引:0
Abstract: During transient cerebral ischemia, there is a temporary and robust accumulation of extracellular GABA in the hippocampus. We examined whether the acute exposure of GABAA /benzodiazepine receptors to high concentrations of GABA early after ischemia results in receptor down-regulation as observed in vitro. Gerbils were killed 30 and 60 min following a 5-min bilateral carotid occlusion, and their brains were prepared for receptor autoradiography. The hydrophilic GABAA receptor antagonist [3 H]SR-95531 and the hydrophobic benzodiazepine agonist [3 H]flunitrazepam were used to distinguish between cell surface and internalized receptors. Ischemia significantly decreased [3 H]SR-95531 binding in hippocampal areas CA1 and CA3 and in the dentate gyrus 30 min after ischemia. Scatchard analysis in area CA1 revealed that ischemia decreased the B max as low as 44%. The affinity of the remaining sites was increased substantially (72% decrease in K D ). As expected, there were no changes in the binding of [3 H]flunitrazepam to hippocampus in the early postischemic period because the benzodiazepine could bind to both internalized receptors and those on the cell surface. We hypothesize that prolonged exposure (∼30–45 min) of GABAA receptors to high concentrations of synaptic GABA in vivo causes receptor down-regulation, perhaps via receptor internalization. 相似文献
3.
Abstract: γ-Aminobutyric acid (GABA) is a major inhibitory neurotransmitter in the mammalian retina, where it serves many roles in establishing complex response characteristics of ganglion cells. We now provide biochemical and physiological evidence that at least three subclasses of GABA receptors (A1, A2, and B) contribute to different types of synaptic integration. Receptor binding studies indicate that approximately three-fourths of the total number of [3 H]GABA binding sites in retina are displaced by the GABAA receptor antagonist, bicuculline, whereas one-fourth are displaced by the GABA-B receptor agonist, baclofen. GABAA receptors can be described by a three-site binding model with KD values of 19 n M , 122 n M , and 5.7 μ M . Benzodiazepines and barbiturates potentiate binding to the GABAA site, which suggests that significant numbers of GABAA receptors are coupled to regulatory sites for these compounds and thus are classified as GABAA1 receptors. The response to pentobarbital appears to involve a conversion of low-affinity sites to higher-affinity sites, and is reflected in changes in the densities of sites at different affinities. Functional studies were used to establish which of the different receptor subclasses regulate release from cholinergic amacrine cells. Our results show that GABA suppresses light-evoked [3 H]acetylcholine release via GABAA2 receptors not coupled to a benzodiazepine or barbiturate regulatory site, and enhances release via GABAB receptors. GABAA1 sites do not appear to control acetylcholine release in rabbit retina. 相似文献
4.
Proenkephalin Gene Regulation in the Paraventricular Nucleus by GABA: Interactions with Opioid Systems in a Transgenic Model 总被引:1,自引:1,他引:0
Abstract: GABA, which is present at high levels within the paraventricular nucleus (PVN) of the hypothalamus, has been implicated in neuroendocrine regulation. Here we use a transgenic mouse model expressing a human proenkephalin-β-galactosidase fusion gene, in which both up-regulation and down-regulation of gene expression can be measured easily, to study the effects of GABA on basal and stress-induced gene expression within the PVN. This model has been shown previously to be appropriately physiologically regulated by stress within the PVN. Acute systemic administration of GABA, of aminooxyacetic acid, and of the selective GABAB receptor agonist, baclofen, induces transgene expression in the PVN. Chronic administration of aminooxyacetic acid inhibits both basal and stress-induced transgene expression. Acute or chronic administration of the selective GABAA agonist, muscimol, inhibits both basal and stress-induced expression of the transgene. Muscimol also inhibits transgene expression in hypothalamic slice cultures in which extrahypothalamic afferents are removed. It is surprising that, following chronic aminooxyacetic acid administration, the opiate antagonist naltrexone induces transgene expression in a manner similar to that observed with naloxone-precipitated opioid withdrawal and that expression is accompanied by a behavioral syndrome that partially mimicks opioid withdrawal. Taken together with our previous work, and using gene expression as our read-out, we conclude that transgene-expressing PVN neurons receive tonic inhibitory inputs mediated via GABAA receptors. Moreover, these inhibitory inputs can themselves be inhibited via GABAB and μ-opioid receptors. 相似文献
5.
The activity of many receptors and ion channels in the nervous system can be regulated by redox-dependent mechanisms. Native and recombinant GABAA receptors are modulated by endogenous and pharmacological redox agents. However, the sensitivity of GABAC receptors to redox modulation has not been demonstrated. We studied the actions of different reducing and oxidizing agents on human homomeric GABAρ1 receptors expressed in Xenopus laevis oocytes. The reducing agents dithiothreitol (2 mM) and N -acetyl- l -cysteine (1 mM) potentiated GABA-evoked Cl− currents recorded by two-electrode voltage-clamp, while the oxidants 5-5'-dithiobis-2-nitrobenzoic acid (500 μM) and oxidized dithiothreitol (2 mM) caused inhibition. The endogenous antioxidant glutathione (5 mM) also enhanced GABAρ1 receptor-mediated currents while its oxidized form GSSG (3 mM) had inhibitory effects. All the effects were rapid and easily reversible. Redox modulation of GABAρ1 receptors was strongly dependent on the GABA concentration; dose–response curves for GABA were shifted to the left in the presence of reducing agents, whereas oxidizing agents produced the opposite effect, without changes in the maximal response to GABA and in the Hill coefficient. Our results demonstrate that, similarly to GABAA receptors and other members of the cys-loop receptor superfamily, GABAC receptors are subjected to redox modulation. 相似文献
6.
Abstract: The multisubunit γ-aminobutyric acid type A (GABAA ) receptor is heterogeneous in molecular and pharmacological aspects. We used quantitative autoradiographic techniques to generate detailed pharmacological profiles for the binding of the GABAA -receptor ionophore ligand tert -[35 S]butylbicyclophosphorothionate ([35 S]TBPS) and its modulation by GABA and the GABAA antagonists bicuculline and 2'-(3'-carboxy-2',3'-propyl)-3-amino-6- p -methoxyphenylpyrazinium bromide (SR 95531). Regional differences in the actions of bicuculline and SR 95531 were correlated with the expression of 13 GABAA subunits in brain as reported previously. In some brain regions SR 95531 reduced [35 S]TBPS binding much more than bicuculline, as illustrated by high ratios of bicuculline- to SR 95531-modulated [35 S]TBPS binding. This ratio correlated positively with α2-subunit mRNA levels. Binding that was equally affected by SR 95531 and bicuculline occurred prominently in regions with abundant α1 mRNA expression. The present findings thus reveal a novel pharmacological heterogeneity based on differences between α1 and α2 subunit-containing GABAA receptors. The data aid in developing GABAA -receptor subtype-specific antagonists and in establishing receptor domains critical for the actions of GABAA antagonists. 相似文献
7.
Expression of Excitatory Amino Acid Receptors by Cerebellar Cells of the Type-2 Astrocyte Cell Lineage 总被引:6,自引:4,他引:2
Vittorio Gallo Claudio Giovannini Rossana Suergiu Giulio Levi 《Journal of neurochemistry》1989,52(1):1-9
Abstract: We have used postnatal rat cerebellar astrocyte-enriched cultures to study the excitatory amino acid receptors present on these cells. In the cultures used, type-2 astrocytes (recognized by the monoclonal antibodies A2B5 and LB1) selectively took up γ-[3 H]aminobutyric acid ([3 H]GABA) and released it when incubated in the presence of micromolar concentrations of kainic and quisqualic acids. The releasing effect of kainic acid was concentration dependent in the range of 5–100 μ M . Quisqualate was more effective than kainate in the lower concentration range but less effective at concentrations at which its releasing activity was maximal (∼50 μ M ). N -Methyl- d -aspartic acid and dihydrokainate (100 μ M ) did not stimulate [3 H]GABA release from cultured astrocytes. l -Glutamic acid (20–100 μ M ) stimulated [3 H]GABA release as effectively as kainate. The stimulatory effects of kainate and quisqualate on [3 H]GABA release were completely Na+ dependent; that of kainate was also partially Ca2+ dependent. Kynurenic acid (50–200 μ M ) selectively antagonized the releasing effects of kainic acid and also that of l -glutamate; quisqualate was unaffected. Quisqualic acid inhibited the releasing effects of kainic acid when both agonists were used at equimolar concentrations (50 μ M ). d -[3 H]aspartate was taken up by both type-1 and type-2 astrocytes, but only type-2 astrocytes released it in the presence of kainic acid. Excitatory amino acid receptors with a pharmacology similar to that of the receptors present in type-2 astrocytes were also expressed by the immature, bipotential progenitors of type-2 astrocytes and oligodendrocytes. 相似文献
8.
Endogenous GABA Modulates Histamine Release from the Anterior Hypothalamus of the Rat 总被引:1,自引:0,他引:1
Kaori Okakura-Mochizuki Takatoshi Mochizuki Yumiko Yamamoto †Arata Horii ‡ Atsushi Yamatodani 《Journal of neurochemistry》1996,67(1):171-176
Abstract: Using a microdialysis method, we investigated the effects of the nipecotic acid-induced increase in content of endogenous GABA on in vivo release of histamine from the anterior hypothalamus (AHy) of urethane-anesthetized rats. Nipecotic acid (0.5 m M ), an inhibitor of GABA uptake, decreased histamine release to ∼60% of the basal level. This effect was partially antagonized by picrotoxin (0.1 m M ), an antagonist of GABAA receptors, or phaclofen (0.1 m M ), an antagonist of GABAB receptors. These results suggest that histamine release is modulated by endogenous GABA through both GABAA and GABAB receptors. When the tuberomammillary nucleus, where the cell bodies of the histaminergic neurons are localized, was stimulated electrically, the evoked release of histamine from the nerve terminals in the AHy was significantly enhanced by phaclofen, suggesting that GABAB receptors may be located on the histaminergic nerve terminals and modulate histamine release presynaptically. On the other hand, picrotoxin caused an increase in histamine release to ∼170% of the basal level, and this increase was diminished by coinfusion with d (−)-2-amino-5-phosphonopentanoic acid (0.1 m M ), an antagonist of NMDA receptors. Previously, we demonstrated tonic control of histamine release by glutamate mediated through NMDA receptors located on the histaminergic terminals in the AHy. These results suggest the possible localization of GABAA receptors on glutamatergic nerve terminals and that the receptors may regulate the basal release of histamine indirectly. 相似文献
9.
Abstract: Previously, it was shown that microinfusion of the GABAA antagonist picrotoxin into the anterior ventral tegmental area (VTA) is reinforcing. It was hypothesized that this reinforcing effect of picrotoxin in the anterior VTA is mediated, at least in part, by the activation of the mesoaccumbens dopamine (DA) system. The objective of the present study was to determine if blockade of GABAA receptors in the anterior VTA can increase extracellular levels of DA in the nucleus accumbens (ACB), using an in vivo microdialysis technique in freely moving rats. Concentrations of picrotoxin (40, 80, and 160 µ M ) that had previously been shown to produce a reinforcing effect increased the extracellular levels of DA and its major metabolites in the ACB. The increased extracellular DA levels induced by intra-VTA injection of picrotoxin was markedly attenuated by coadministration with the GABAA agonist muscimol, whereas intra-VTA injection of muscimol alone did not have an apparent effect on extracellular DA levels in the ACB. Microinjection of another GABAA antagonist, bicuculline, into the anterior VTA also increased the extracellular release of DA in the ACB. These results suggest that DA neurons projecting from the anterior VTA to the ACB are tonically inhibited by GABA through its actions at the GABAA receptors. 相似文献
10.
UPTAKE AND METABOLISM OF GLUTAMATE IN ASTROCYTES CULTURED FROM DISSOCIATED MOUSE BRAIN HEMISPHERES 总被引:21,自引:20,他引:1
Abstract— Uptake kinetics of l -glutamate in cultured, normal glia cells obtained from the brain hemispheres of newborn mice were measured together with the activities of the glutamate metabolizing enzymes, glutamic-oxaloacetate-transaminase, glutamate dehydrogenase and glutamine synthetase. During 3 weeks of culturing, the activities of the enzymes rose from low neonatal values toward the levels in the adult brain (206, 12.3 and 25.9 nmol. min−1 . mg−1 cell protein for the three enzymes, respectively). The uptake kinetics indicated an unsaturable component together with an uptake following Michaelis-Menten kinetics with a Km of 220 μ m and a V max of 7.9 nmol. min−1 . mg−1 cell protein. The saturable glutamate uptake was inhibited by d -glutamate, l -aspartate and α-aminoadipate whereas l -glutamine, GABA and glutarate had no effect. The uptake which was Ca2+ -independent had a Km for sodium of 18m m and it was stimulated by an increase in the external potassium concentration from 5 to 10 and 25 m m. The results suggest that glia cells are important for the uptake of glutamate from synaptic clefts and for the subsequent metabolism of glutamate. 相似文献
11.
Fatima A. Nasrallah Julian L. Griffin† Vladimir J. Balcar‡ Caroline Rae§ 《Journal of neurochemistry》2009,108(1):57-71
A targeted neuropharmacological, 1 H/13 C NMR spectroscopy and multivariate statistical approach was used to examine the effects of exogenous GABA and ligands at the GABAA receptor family on brain metabolism in the Guinea pig cortical tissue slice. All ligands at GABAA receptors generated metabolic patterns which were distinct from one another with the major variance in the data arising because of metabolic work (shown by net flux into Krebs cycle byproducts and increased metabolic pool sizes). Three major clusters of metabolic signatures were identified which corresponded to: (i) activity at phasic (synaptic) GABAA receptors, dominated by α1-containing receptors and responsive to GABA at 10 μmol/L; (ii) activity at perisynaptic receptors, dominated by response to high (40 μmol/L) GABA and the superagonist 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridine-3-ol hydrochloride, and C, activity at extrasynaptic receptors, dominated by response to low (0.1–1.0 μmol/L) GABA, zolpidem (400 nmol/L) and the non-specific allosteric modulator RO19-4603 (1 nmol/L). These results highlight the utility of a different but robust approach to study of the GABAergic system using metabolic systems analysis. 相似文献
12.
Stephen J. Morris Diane M. Beatty Bibie M. Chronwall 《Journal of neurochemistry》1998,71(3):1329-1332
Abstract: GABAB and dopamine D2 receptors, both of which acutely inhibit adenylyl cyclase and high voltage-activated Ca2+ channels (HVA-CCs), are found in high levels in the melanotrope cells of the pituitary intermediate lobe. Chronic D2 receptor agonist application in vitro has been reported to result in inhibition of HVA-CC activity by down-regulation. Here we report that chronic GABAB , but not GABAA , agonist treatment also resulted in HVA-CC inhibition. Two GABAB receptor variants have been cloned and shown to inhibit adenylyl cyclase in HEK-293 cells. We have constructed an antisense deoxynucleotide knockdown-type probe that is complementary to 18 bp from the point at which the two sequences first become homologous. Chronic coincubation with baclofen and GABAB antisense nucleotide completely eliminated the inhibition of the channels by baclofen alone but had no reversing effect on HVA-CC inhibition by the D2 agonist quinpirole. A scrambled, missense nucleotide also had no reversing effect. Incubation with a D2 antisense knockdown probe eliminated the ability of a D2 agonist to inhibit the channels but had no effect on baclofen blockade. These results show the existence an R1a/R1b type of GABAB receptor, which, like the D2 receptor, is coupled to chronic HVA-CC inhibition in melanotropes. 相似文献
13.
Lysophosphatidic Acid Induces a Sustained Elevation of Neuronal Intracellular Calcium 总被引:4,自引:2,他引:2
Frederick W. Holtsberg Marion R. Steiner †Katsutoshi Furukawa Jeffrey N. Keller †Mark P. Mattson Sheldon M. Steiner 《Journal of neurochemistry》1997,69(1):68-75
Abstract: Lysophosphatidic acid (LPA) is a lipid biomediator enriched in the brain. A novel LPA-induced response in rat hippocampal neurons is described herein, namely, a rapid and sustained elevation in the concentration of free intracellular calcium ([Ca2+ ]i ). This increase is specific, in that the related lipids phosphatidic acid and lysophosphatidylcholine did not induce an alteration in [Ca2+ ]i . Moreover, consistent with a receptor-mediated process, there was no further increase in [Ca2+ ]i after a second addition of LPA. The LPA-induced increase in [Ca2+ ]i required extracellular calcium. However, studies with Cd2+ , Ni2+ , and nifedipine and nystatin-perforated patch clamp analyses did not indicate involvement of voltage-gated calcium channels in the LPA-induced response. In contrast, glutamate appears to have a significant role in the LPA-induced increase in [Ca2+ ]i , because this increase was inhibited by NMDA receptor antagonists and α-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA)/kainate receptor antagonists. Thus, LPA treatment may result in an increased extracellular glutamate concentration that could stimulate AMPA/kainate receptors and thereby alleviate the Mg2+ block of the NMDA receptors and lead to glutamate stimulation of an influx of calcium via NMDA receptors. 相似文献
14.
An mRNA Encoding a Putative GABA-Gated Chloride Channel Is Expressed in the Human Cardiac Conduction System 总被引:1,自引:0,他引:1
Maurice Garret Lionel Bascles Eric Boue-Grabot Pierre Sartor Gisele Charron Bertrand Bloch †Robert F. Margolskee 《Journal of neurochemistry》1997,68(4):1382-1389
Abstract: GABA-gated chloride channels are the main inhibitory neurotransmitter receptors in the CNS. Conserved domains among members of previously described GABAA receptor subunits were used to design degenerate sense and antisense oligonucleotides. A PCR product from this amplification was used to isolate a full-length cDNA. The predicted protein has many of the features shared by other members of the ligand-gated ion channel family. This channel subunit has significant amino acid identity (25–40%) with members of GABAA and GABAC receptor subunits and thus may represent a new subfamily of the GABA receptor channel. Although we cannot rule out that this clone encodes a receptor for an unidentified ligand, it was termed GABA χ . This gene is mainly expressed in placenta and in heart; however, placenta appears to express only an unspliced mRNA. In situ hybridization reveals that the GABA χ subunit mRNA is present in the electrical conduction system of the human heart. Our results suggest that novel GABA receptors expressed outside of the CNS may regulate cardiac function. 相似文献
15.
Llansola Marta Hermenegildo Carlos Miñana María-Dolores Felipo Vicente 《Neurochemical research》1998,23(6):913-918
We observed that AP-3, an antagonist of metabotropic glutamate receptors, reduced carbachol-induced hydrolysis of phospholipids in hippocampal slices. This inhibition could be explained in different ways, e.g.: 1) AP-3 acts also as antagonist of muscarinic receptors mediating the hydrolysis of phospholipids induced by carbachol, 2) Carbachol induces the release of glutamate which, by activating metabotropic glutamate receptors, leads to additional hydrolysis of phospholipids. The aim of this work was to test these possibilities. It is shown that AP-3 reduces carbachol-induced hydrolysis of phospholipids in hippocampal slices but not in cerebellar neurons at 10–14 days of culture, when these cells are not able to induce hydrolysis of phospholipids following activation of metabotropic glutamate receptors. It is also shown that carbachol induces a release of [3H]aspartate in hippocampal slices. The results reported suggest that the hydrolysis of phospholipids induced by carbachol in hippocampal slices would have two components. One part would be due to direct activation by carbachol of muscarinic receptors associated to activation of phospholipase C. This part would not be inhibited by AP-3. The second part would be due to subsequent release of glutamate and activation of metabotropic glutamate receptors. This part would be inhibited by AP-3. 相似文献
16.
Giovanni Fontana Roberto De Bernardi Federico Ferro Anita Gemignani Maurizio Raiteri 《Journal of neurochemistry》1996,66(1):161-168
Abstract: l -Glutamate, NMDA, dl -α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA), and kainate (KA) increased the release of somatostatin-like immunoreactivity (SRIF-LI) from primary cultures of rat hippocampal neurons. In Mg2+ -containing medium, the maximal effects (reached at ∼100 µ M ) amounted to 737% (KA), 722% (glutamate), 488% (NMDA), and 374% (AMPA); the apparent affinities were 22 µ M (AMPA), 39 µ M (glutamate), 41 µ M (KA), and 70 µ M (NMDA). The metabotropic receptor agonist trans -1-aminocyclopentane-1,3-dicarboxylate did not affect SRIF-LI release. The release evoked by glutamate (100 µ M ) was abolished by 10 µ M dizocilpine (MK-801) plus 30 µ M 1-aminophenyl-4-methyl-7,8-methylenedioxy-5 H -2,3-benzodiazepine (GYKI 52466). Moreover, the maximal effect of glutamate was mimicked by a mixture of NMDA + AMPA. The release elicited by NMDA was sensitive to MK-801 but insensitive to GYKI 52466. The AMPA- and KA-evoked releases were blocked by 6,7-dinitroquinoxaline-2,3-dione (DNQX) or by GYKI 52466 but were insensitive to MK-801. The release of SRIF-LI elicited by all four agonists was Ca2+ dependent, whereas only the NMDA-evoked release was prevented by tetrodotoxin. Removal of Mg2+ caused increase of basal SRIF-LI release, an effect abolished by MK-801. Thus, glutamate can stimulate somatostatin release through ionotropic NMDA and AMPA/KA receptors. Receptors of the KA type (AMPA insensitive) or metabotropic receptors appear not to be involved. 相似文献
17.
In addition to their role in orchestrating body and tentacle contractions, hydra’s nerves control the behavior of nematocysts;
precisely how is still a work in progress. There are strong indications that the classical neurotransmitters, glutamate and
GABA (γ-amino-butyric acid), play an essential role in effecting stenotele and desmoneme discharge. In experiments on isolated
tentacles of Hydra vulgaris, in which cnidocils were mechanically deflected with a piezo-electrically-driven glass micropipette, stenoteles and desmonemes
respond to differences in applied force in a dose-dependent manner. GABA, working through its metabotropic receptor, appears
to be involved with the recruitment of desmonemes. Desmonemes in distant battery cells or in another part of a given battery
cell were discharged by stimulating a desmoneme cnidocil in the presence of bath-applied GABA or its metabotropic agonist,
baclofen. The effect was blocked by phaclofen, its metabotropic antagonist. Neither GABA nor baclofen affected stenotele discharge.
GABAA agonists had no effect on nematocyst discharge. Glutamate caused a significant increase in number of stenoteles responding
to direct mechanical stimuli, but did not effect desmoneme discharge. The effect was mimicked by NMDA (n-methyl-d-aspartate) together with kainate, or by NMDA plus AMPA (amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid), but not with
any ionotropic agonist alone. The effect was blocked by D-AP 5 (d- (−)–2-amino–5-phosphopentanoic acid), a specific NMDA antagonist, or CNQX (6-cyano-7-nitroquinoxaline-2,3-dione), a specific
kainate/AMPA antagonist. A glutamatergic mechanism working through ionotropic glutamate receptors appears to lower the firing
threshold of stenoteles, perhaps␣by permitting the entry of Ca2+ into the cell through the early evolved NMDA/kainite/AMPA mechanism. 相似文献
18.
Interactions Between N-Acetylaspartylglutamate and AMPA, Kainate, and NMDA Binding Sites 总被引:2,自引:2,他引:0
H. Mohammed Valivullah Jean Lancaster Paul M. Sweetnam Joseph H. Neale 《Journal of neurochemistry》1994,63(5):1714-1719
Abstract: The structure of N -acetylaspartylglutamate (NAAG) suggests this neuronal dipeptide as a candidate for interaction with discrete subclasses of ionotropic and metabotropic acidic amino acid receptors. A substantial difficulty in the assay of these interactions is posed by membrane-bound peptidase activity that converts the dipeptide to glutamate and N -acetylaspartate, molecules that will interfere with receptor assays. We have developed two sets of unique receptor assay conditions and applied one standard assay to measure the interactions, under equilibrium binding conditions, of [3 H]kainate, [3 H]amino-3-hydroxy-5-methylisoxazole-4-propionic acid ([3 H]AMPA), and [3 H]CGS-19755 with the three classes (kainate, quisqualate, and N -methyl- d -aspartate) of ionotropic glutamate receptors, while inhibiting peptidase activity against NAAG. Under these conditions, NAAG exhibits apparent inhibition constants (IC50 ) of 500, 790, and 8.8 µ M in the kainate, AMPA, and CGS-19755 receptor binding assays, respectively. Glutamate was substantially more effective and less specific in these competition assays, with inhibition constants of 0.36, 1.1, and 0.37 µ M . These data support the hypothesis that, relative to glutamate, NAAG functions as a specific, low potency agonist at N -methyl- d -aspartate subclass of ionotropic acidic amino acid receptors, but the peptide is not likely to activate directly the kainate or quisqualate subclasses of excitatory ionotropic receptors under physiologic conditions. 相似文献
19.
Abstract: GTP and GDP decreased the saturable binding of [3 H]baclofen or [3 H]γ-aminobutyric acid ([3 H]GABA) to GABAB but not GABAA receptors whereas GMP displayed negligible activity. This effect was specific to guanyl nucleotides and was not mimicked by high concentrations of ATP. The inhibition of ligand binding was the result of a diminished receptor affinity with no change in receptor number. The use of a complete physiological saline solution rather than Tris buffer plus Ca2+ or Mg2+ increased the potency of GTP at the GABAB receptor. The results are discussed in relation to the effects of GABA and GTP on adenylate cyclase activity in the brain. 相似文献
20.
Distinct Loci Mediate the Direct and Indirect Actions of the Anesthetic Etomidate at GABAA Receptors
† Eric J. Moody †Christopher Knauer Ricardo Granja Marina Strakhova †Phil Skolnick 《Journal of neurochemistry》1997,69(3):1310-1313
Abstract: Most general anesthetics produce two distinct actions at GABAA receptors. Thus, these drugs augment GABA-gated chloride currents (referred to as an indirect action) and, at higher concentrations, elicit chloride currents in the absence of GABA (referred to as a direct action). Because a β subunit appears to be required for the direct action of intravenous anesthetics in recombinant GABAA receptors, site-directed mutagenesis of the β3 subunit was performed to identify amino acid residues that are critical for this action. In HEK293 cells expressing a prototypical GABAA receptor composed of α1β3γ2 subunits, mutation of amino acid 290 from Asn to Ser dramatically reduced both etomidate-induced chloride currents and its ability to stimulate [3 H]flunitrazepam binding. By contrast, the ability of etomidate to augment GABA-gated chloride currents and GABA-enhanced [3 H]flunitrazepam binding was retained. The demonstration that the direct, but not the indirect, actions of etomidate are dependent on β3(Asn290 ) indicates that the dual actions of this intravenous anesthetic at GABAA receptors are mediated via distinct loci. 相似文献