Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Guanine nucleotides have been examined as to their effects on subclass-specific excitatory amino acid receptor-ligand interactions. Guanine nucleotides selectively inhibit L-[3H]glutamate binding to the N-methyl-D-aspartate (NMDA) recognition site while showing a lesser effect on [3H]kainate, [3H]alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate and sodium-dependent L-[3H]glutamate binding. Of the series of guanine nucleotides tested in the inhibition of NMDA-specific L-[3H]glutamate binding, GTP, GDP, 5'-guanylylimidodiphosphate and 5'-guanylylmethylenediphosphate were significantly more potent than GMP, cyclic GMP and guanosine. Scatchard analysis indicates that the GTP inhibition (IC50 = 28 microM) of this NMDA-specific L-[3H]glutamate binding results from a decrease in the affinity of L-glutamate for the NMDA receptor whereas no alteration in the number of binding sites is observed. A kinetic analysis indicates that this decrease in affinity may be attributed to a decrease in association rate whereas no change in dissociation rate is observed. GTP (25 microM) lowers the affinities of both NMDA agonists (NMDA, L-glutamate, L-aspartate, and L-homocysteate) and antagonists (D-2-amino-5-phosphonovalerate, D-2-amino-7-phosphonoheptanoate, and D-2-aminoadipate). Pretreatment of the synaptic plasma membranes with either pertussis or cholera toxin had no significant effect on the GTP inhibition of NMDA-specific L-[3H] glutamate binding. The data suggest that guanine nucleotides can negatively modulate the NMDA receptor; however, the mechanism of this modulation is unclear.
Mol Pharmacol 1988 Aug
PMID:Effects of guanine nucleotides on N-methyl-D-aspartate receptor-ligand interactions. 284 50

N-Methyl-D-aspartate (NMDA) receptor ligands regulate the binding of uncompetitive antagonists in membranes prepared from rat brain. To determine the mechanism of this regulation, we examined the kinetics of the binding of the radiolabeled uncompetitive antagonist [3H]N-(1-[thienyl]cyclohexyl) piperidine (TCP). Increasing concentrations of NMDA receptor agonists produced dose-dependent increases in the association and dissociation rate constants of TCP. The NMDA receptor antagonist amino phosphono valeric acid virtually abolished both the association and dissociation of TCP. Linear regression analysis detected a significant (p less than 0.001) correlation between the effect of NMDA receptor ligands on the apparent association and dissociation rate constants. The most parsimonious explanation of the data is that NMDA receptor ligands regulate TCP binding by controlling access of TCP to a transiently accessible or "guarded" binding site located in the receptor-coupled ion channel. An increase in affinity or number of TCP binding sites is neither necessary nor sufficient to explain the potentiation of TCP binding produced by NMDA agonists. This finding validates the use of uncompetitive antagonist binding as a measure of the functional activation of the NMDA receptor-coupled ion channel in isolated membrane preparations.
Mol Pharmacol 1988 Sep
PMID:N-methyl-D-aspartate receptor regulation of uncompetitive antagonist binding in rat brain membranes: kinetic analysis. 284 44

Intracellular recordings were obtained from guinea pig hippocampal neurons maintained in vitro. Current- and voltage-clamp techniques were used to study the effect of microiontophoresis of excitatory amino acid agonists. Modification of agonist responses by bath application of known concentrations of antagonist agents was also examined. All agonists used, glutamate, aspartate, N-methyl-D-aspartic acid (NMDA), and quisqualate, depolarized hippocampal neurons and caused repetitive firing. NMDA was also noted to induce burst-firing in some neurons. Quisqualate and NMDA were more potent than glutamate or aspartate. In slices perfused with a nominally calcium-free saline containing tetrodotoxin and manganese, quisqualate application produced a depolarization associated with a conductance increase. Under those conditions, NMDA-induced depolarizations caused apparent decreases as well as increases in conductance. The apparent decreases in conductance were observed in the voltage range of -40 to -70 mV, whereas increases in conductance were observed at membrane potentials more positive than -35 mV. Under voltage-clamp conditions, quisqualate produced an inward current whose amplitude increased with hyperpolarization and decreased upon depolarization, reversing near 0 mV. The conductance change induced by quisqualate was independent of voltage. NMDA application resulted in an inward current that was maximal around the resting potential and decreased with both hyperpolarization and depolarization. Response reversal was not observed with hyperpolarization to -100 mV but was apparent with depolarization beyond 0 mV. Conductance changes induced by NMDA were voltage dependent, and the application of this agent was associated with the appearance of a region of negative slope conductance in the current-voltage relationship. Apparent decreases in conductance in response to NMDA were reduced when the extracellular magnesium concentration was lowered. Response amplitudes were not affected. The NMDA receptor antagonist DL-2-amino-5-phosphonovalerate (DL-APV) was a potent and selective blocker of NMDA responses, whereas the antagonist DL-2-amino-4-phosphonobutyric acid (DL-APB) was less potent and did not select between NMDA and quisqualate responses. Analysis of iontophoretic dose-response curves indicated that DL-APV was a competitive antagonist. The results of these experiments indicate that hippocampal CA1 pyramidal neurons possess separate receptors for quisqualate and NMDA, with different pharmacological and electrophysiological profiles.
Cell Mol Neurobiol 1985 Dec
PMID:Action of excitatory amino acids and their antagonists on hippocampal neurons. 286 26

Biochemical and electrophysiological studies have provided evidence that a complex comprising the N-methyl-D-aspartate (NMDA)-type excitatory amino acid (EAA) receptor and the phencyclidine (PCP) recognition site exists in mammalian brain. This complex, which has been compared to that established for the inhibitory amino acid, gamma-aminobutyric acid, and the benzodiazepine anxiolytic, diazepam, is sensitive to the effects of the divalent cation Mg2+, which has suggested the presence of a third, ion channel component. Using a radioreceptor assay for the PCP receptor, L-glutamate (L-Glu) produced a concentration-dependent increase in the binding of [3H]thienyl cyclohexylpiperazine ([3H]TCP) in well washed membranes from rat forebrain. The EAA produced a maximal increase in specific binding of 400%, with an EC50 value of 340 nM. The ability of L-Glu to enhance [3H]TCP binding was 10-fold more potent in the presence of 30 microM Mg2+, which inhibits NMDA-evoked responses in intact tissue preparations and produces a 50% increase in [3H]TCP binding on its own. Analysis of saturation curves indicated that the effect of both L-Glu and Mg2+ could be attributed to an increase in receptor affinity as well as increases in the proportion of a high affinity state of the PCP-binding site. Assessment of the effect of a number of EAAs on basal [3H]TCP binding (well washed membranes in the absence of either L-Glu or Mg2+) showed that the EAA recognition site involved in the effects of L-Glu was the NMDA subtype. Further studies examined a series of compounds thought to interact with either the NMDA or PCP components of the receptor complex under four binding conditions: basal, +Mg2+; +L-Glu; and +Mg2+/L-Glu. These results showed that dissociative anesthetics, such as dexoxadrol and PCP, as well as the novel anticonvulsant MK-801, selectively interact with the high affinity state of the PCP receptor. NMDA antagonists, such as CPP, were also found to inhibit binding to the high affinity state of the PCP receptor, although not as potently as the dissociative anesthetics. Interestingly, the NMDA antagonists did not inhibit any of the binding to the low affinity state of the receptor. The sigma ligands (+/-)-SKF 10,047 and haloperidol recognized two components of [3H]TCP binding only in the presence of L-Glu. The results of the present study are consistent with the finding that agonists of the NMDA receptor induce a high affinity state of the PCP receptor.
Mol Pharmacol 1987 Dec
PMID:Interaction of L-glutamate and magnesium with phencyclidine recognition sites in rat brain: evidence for multiple affinity states of the phencyclidine/N-methyl-D-aspartate receptor complex. 289 25

Functional roles of peroxynitrite in N-methyl-D-aspartate (NMDA)- and sodium nitroprusside (SNP)-evoked releases of acetylcholine (ACh) from cerebral cortical neurons in primary culture have been investigated. NMDA increased the release of ACh in a dose-dependent manner, which was significantly suppressed by (+)-5-methyl-10,11-dihydro-5H-dibenzo-[a,d]cycloheptan-5,10-imine (MK-801), a non-competitive antagonist specific for the NMDA receptor complex, and NO synthase inhibitors. SNP also showed a concentration-dependent increase in ACh release. Hemoglobin significantly abolished the stimulatory effects of both NMDA and SNP on ACh release. In addition, superoxide anion scavengers such as superoxide dismutase and ceruloplasmin significantly reduced the increased ACh release evoked by NMDA and SNP. Synthesized peroxynitrite dose-dependently elevated the release of ACh. These results indicate that the increased release of ACh by NMDA and SNP is mediated through peroxynitrite formed in the reaction of superoxide anion with nitric oxide produced by NMDA receptor activation and liberated from SNP rather than nitric oxide itself.
Brain Res Mol Brain Res 1995 Jul
PMID:Involvement of peroxynitrite in N-methyl-D-aspartate- and sodium nitroprusside-induced release of acetylcholine from mouse cerebral cortical neurons. 747 28

Ethanol inhibits N-methyl-D-aspartate (NMDA) receptor-mediated responses at pharmacologically relevant concentrations, suggesting that inhibition of NMDA receptors may underlie some of the actions of ethanol in the central nervous system. We examined the ability of glycine to modulate ethanol inhibition of four recombinant heteromeric NMDA receptors (NR1a/NR2A through NR2D) expressed in Xenopus oocytes. Ethanol dose-response analysis revealed enhanced inhibitory efficacy of ethanol in the presence of subsaturating glycine concentrations at the NR1/NR2A, NR1/NR2C, and NR1/NR2D receptors. When assayed over a range of glycine concentrations, ethanol exhibited both glycine-reversible and glycine-independent inhibition of NMDA receptors. In contrast, ethanol inhibition of recombinant NMDA receptors was independent of NMDA concentration. Glycine reversal of ethanol inhibition suggested that ethanol might lower the affinity of glycine for the NMDA receptor and thereby decrease response magnitude. Consistent with this hypothesis, ethanol significantly reduced glycine affinity at NR1/NR2A and NR1/NR2C receptors. Evaluation of the glycine-independent component of ethanol inhibition demonstrated that in the presence of saturating concentrations of glycine, the NR1/NR2A and NR1/NR2B receptors were more sensitive to ethanol than the NR1/NR2C and NR1/NR2D receptors. Activation of the NR1/NR2D heteromers by NMDA and low concentrations of glycine elicited responses characterized by an initial peak followed by a lower-amplitude plateau response, which is consistent with glycine-sensitive desensitization as previously described for native NMDA receptors. In addition, nondesensitizing NR1/NR2B responses elicited in the presence of subsaturating concentrations of glycine were frequently converted into desensitizing responses by the addition of ethanol, an effect that was reversed with increasing glycine concentrations. The ability of ethanol to promote glycine-sensitive desensitization further suggests an interaction between glycine and ethanol inhibition of the NMDA receptor. Taken together, the results of the present report demonstrate that ethanol inhibition of NMDA receptors has both glycine-reversible and glycine-independent components, suggesting two distinct molecular mechanisms for ethanol inhibition of NMDA receptors.
Mol Pharmacol 1995 Oct
PMID:Glycine modulates ethanol inhibition of heteromeric N-methyl-D-aspartate receptors expressed in Xenopus oocytes. 747 99

The pharmacological properties of two recombinant human N-methyl-D-aspartate (NMDA) receptor subtypes, comprising either NR1a/NR2A or NR1a/NR2B subunits permanently transfected into mouse L(tk-) cells, have been compared using whole-cell voltage-clamp electrophysiology. Glutamate was a full agonist at both receptors, having a modestly but statistically significant (p < 0.002) higher affinity for the NR2B- than the NR2A-containing receptor (microscopic Kd [mKd] = 0.76 and 0.43 microM, respectively). In comparison to glutamate, NMDA, quinolinic acid, and cis-2,3-piperidinedicarboxylic acid were partial agonists at both receptor subtypes. Maximal amplitude currents resulted when glutamate-site agonists were combined with either glycine or D-serine; both of these amino acids were, therefore, defined as full agonists at the glycine site. Glycine had an approximately 10-fold higher affinity (p < 0.0001) for NR2B- than for NR2A-containing receptors (mKd = 0.057 and 0.53 microM, respectively). D-Cycloserine, (+)-(3R)-3-amino-1-hydroxypyrrolidin-2-one, (+)-cis-(4R)-methyl-(3R)-amino-1-hydroxypyrrolidin-2-one, and 1-aminocyclobutanecarboxylic acid also had higher affinities for the NR2B-containing receptor but were partial agonists, at both receptor subtypes, unlike glycine. Agonist-evoked whole-cell currents were antagonized by D-(-)-2-amino-5-phosphonopentanoic acid, cis-4-(phosphonomethyl)piperidine-2-carboxylic acid, and 3-((R)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid, all of which had slightly, but statistically significant, higher affinities (2.2-, 2.8-, and 5.5-fold, respectively) for the NR2A-containing receptor. Responses were also antagonized by the glycine-site antagonists 7-chlorokynurenic acid, 7-chloro-4-hydroxy-3-(3-phenoxy)phenylquinolin-2-(1H)-one, and (+/=)-4-(trans)-2-carboxy-5,7-dichloro-4-phenylaminocarbonylamino- 1,2,3,4- tetrahydroquinoline. The atypical NMDA antagonist ifenprodil showed the largest separation in functional affinity (IC50 values, 0.6 and 175 microM at NR2B- and NR2A-containing receptors, respectively). These experiments demonstrate the usefulness of permanently transfected L(tk-) cells for electrophysiological studies of recombinant NMDA receptor function and provide the first detailed functional pharmacological analysis of human NMDA receptor subtypes.
Mol Pharmacol 1995 Nov
PMID:Pharmacological properties of recombinant human N-methyl-D-aspartate receptors comprising NR1a/NR2A and NR1a/NR2B subunit assemblies expressed in permanently transfected mouse fibroblast cells. 747 14

We have shown previously that the neurosteroid pregnenolone sulfate acts as a positive allosteric modulator at the N-methyl-D-aspartate (NMDA) receptor while inhibiting the kainate, the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA), the glycine, and the gamma-aminobutyric acid (GABA) responses of chick spinal cord neurons. Here, we report that 3 alpha-hydroxy-5 beta-pregnan-20-one sulfate (5 beta 3 alpha S), a sulfated form of naturally occurring 5 beta 3 alpha, inhibits both the NMDA and the non-NMDA receptor-mediated responses as measured by whole cell voltage clamp recordings. 100 microM 5 beta 3 alpha S rapidly and reversibly inhibits the response to 30 microM NMDA by 66%, 50 microM kainate by 37%, and 25 microM AMPA by 29%. Application of 50 microM nonsulfated 5 beta 3 alpha does not produce any significant effect on the NMDA response, demonstrating that the sulfate moiety is important for the effect of 5 beta 3 alpha S on the NMDA response. The effect of 5 beta 3 alpha S on the NMDA response is concentration dependent, with an EC50 of 62 microM. 5 beta 3 alpha S reduces the maximum NMDA response with little effect on the NMDA EC50, indicating that antagonism of the NMDA response by 5 beta 3 alpha S is noncompetitive. The fact that 5 beta 3 alpha S inhibition of the NMDA response is neither agonist nor voltage dependent demonstrates that 5 beta 3 alpha S does not act as an open channel blocker. Furthermore, inhibition of the NMDA response by 5 beta 3 alpha S is not reduced by the addition of a maximal concentration (10 microM) of glycine, indicating that 5 beta 3 alpha S does not act via the glycine recognition site. The inhibitory action of 5 beta 3 alpha S on the NMDA and non-NMDA receptors may provide a basis for inhibiting glutamate receptor-induced seizures and excitotoxic cell death.
Mol Pharmacol 1994 Jul
PMID:3 alpha-Hydroxy-5 beta-pregnan-20-one sulfate: a negative modulator of the NMDA-induced current in cultured neurons. 752 Jan 24

The effects of alkylene bis-9,9'-aminoacridines and 1,2,3,4-tetrahydro-9-aminoacridine (THA) were studied on single-channel currents activated by N-methyl-D-aspartate (NMDA) in outside-out patches from cultured rat hippocampal neurons. These compounds reduced the channel open times with concentration and voltage dependence, which was consistent with an open-channel blockade mechanism of action. In nominally Mg(2+)-free solutions, the forward blocking rate constants for 1,2-propane-bis-9,9'-aminoacridine, 1,4-butane-9,9'-aminoacridine, and THA were 1.1 x 10(8), 1.4 x 10(8), and 3.5 x 10(7) M-1 sec-1, respectively, at a holding potential of -80 mV. The unblocking rate constants for the bis-9-aminoacridines were similar and in the range of 7 sec-1, whereas THA had an unblocking rate constant of approximately 6.2 x 10(3) sec-1. In the presence of Mg2+ (approximately 5 microM), the predictions of the model for open-channel blockade by the 9-aminoacridines were invalid, because the relationships between the channel lifetimes and 9-aminoacridine concentrations were not linear. The effects of Mg2+ (approximately 0-50 microM) on the open-channel blockade of the NMDA receptor by the 9-aminoacridines were evaluated further by measuring the burst times in the presence of 1,2-propane-bis-9,9'-aminoacridine (5 microM). The results suggested that the interactions of 9-aminoacridines and Mg2+ with the ion channel of the NMDA receptor were not mutually exclusive. Simultaneous occupancy of the NMDA receptor ion channel by Mg2+ and a channel-blocking organic cation could be a common mechanism of channel blockade for this receptor under physiological conditions.
Mol Pharmacol 1994 Jul
PMID:9-Aminoacridines act at a site different from that for Mg2+ in blockade of the N-methyl-D-aspartate receptor channel. 752 Jan 25

The heteromeric mouse epsilon 2/zeta 1 N-methyl-D-aspartate (NMDA) receptor was expressed in Xenopus oocytes, and its channel properties were studied using both the outside-out patch-clamp and two-microelectrode voltage-clamp techniques. In the cloned receptor channel, permeation properties of monovalent and divalent cations, and voltage-dependent block by Mg2+ were similar to those reported previously in the native NMDA receptor channels. The sequence of single-channel conductances for alkali metals was Rb+ > Cs+ approximately K+ > Na+ > Li+, whereas the sequence of relative permeabilities was Cs+ > Rb+ > K+ approximately Na+ > Li+. The single-channel conductances measured in isotonic Ca2+, Sr2+ and Ba2+ solutions were almost equal, and approximately one-fifth of the value in the Na+ solution, although the permeabilities for these alkaline earth cations were higher than for Na+. It is likely that Ca2+, Sr2+ and Ba2+ would enter the NMDA receptor channel more easily than Na+, but would bind to a site in the channel more tightly, the net effect being a reduced value of the current.
Brain Res Mol Brain Res 1994 Oct
PMID:Ion permeation properties of the cloned mouse epsilon 2/zeta 1 NMDA receptor channel. 753 4


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