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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Spermine potentiates the action of N-methyl-D-aspartate (NMDA) at micromolar concentrations but is less effective at millimolar concentrations. In cultured cortical neurons we demonstrate that spermine enhances NMDA receptor currents in a unique manner. At low concentrations (1-10 microM) spermine enhances NMDA receptor current by increasing channel opening frequency, and at higher concentrations (greater than 10 microM) it produces, in addition, a voltage-dependent decrease in channel amplitude and average open time that limits its enhancing action. It is likely that these two actions of spermine, due to differences in concentration and voltage dependence, are mediated by independent sites on the NMDA receptor complex.
Mol Pharmacol 1992 Jan
PMID:The polyamine spermine has multiple actions on N-methyl-D-aspartate receptor single-channel currents in cultured cortical neurons. 137 Jul 9

In cultured spinal cord neurons, we found that blockers of chloride transport (furosemide, a widely used loop diuretic, and the related compounds piretanide and bumetanide, as well as niflumic and flufenamic acids, used as antiinflamatory agents) prevented N-methyl-D-aspartate (NMDA) receptor activation in a dose-dependent manner and are specific for this class of glutamate receptor. Antagonism of NMDA-mediated currents by chloride transport blockers was voltage independent and showed fast on-ff kinetics. The action was noncompetitive with NMDA and did not arise from interaction with the Zn2+ inhibitory site, because blockade of NMDA-induced responses by furosemide and Zn2+ was additive. The inhibition was greater in a low concentration of glycine, but it could not be overcome by increasing the glycine concentration (up to 100 microM). In contrast, the inhibition was attenuated by the polyamine spermine. Because the presence of spermine was not required for inhibition to develop, we conclude that chloride transport blockers are noncompetitive antagonists of the NMDA receptor, likely acting as inverse agonists of the polyamine site. This action may explain the protective effect that has been shown for some of these drugs in neuronal degeneration; because they also prevent neuronal swelling, they may be good starting compounds for synthesis of appropriate therapeutic agents to ameliorate excitotoxicity.
Mol Pharmacol 1992 Feb
PMID:Chloride transport blockers prevent N-methyl-D-aspartate receptor-channel complex activation. 137 81

The inhibitory potencies at excitatory amino acid (EAA) receptors of 11 quinoxaline derivatives were evaluated in two-electrode voltage-clamp recordings of Xenopus oocytes injected with rat cortex mRNA. Currents activated by kainate or (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) in Xenopus oocytes were inhibited competitively by all the quinoxaline derivatives, with apparent Ki values ranging from 0.27 to 300 microM against kainate and from 0.25 to 137 microM against AMPA. An excellent correlation was observed between inhibitory potencies of the quinoxaline derivatives against kainate and AMPA currents, in support of the contention that in this preparation these two agonists act at a single site. All 11 quinoxaline derivatives also inhibited current activated by the combination of glycine and N-methyl-D-aspartate (NMDA), apparently acting at the glycine site, and did so over a narrower range of apparent Ki values (0.37-8.1 microM). The correlation between the quinoxalines' kainate/AMPA potencies and their glycine/NMDA potencies was relatively weak. Thus, the quinoxaline derivatives were all good antagonists of glycine/NMDA currents and displayed a greater range of potencies against kainate and AMPA. The inhibitory effects of the six quinoxaline derivatives most potent in the Xenopus oocyte experiments were also tested against the excitatory postsynaptic field potential (EPSFP) recorded in the pyramidal cell dendritic field of the CA1 region of hippocampal slices after stimulation of the Schaffer collateral-commissural pathways. In slices superfused with "normal" medium (containing 1 mM Mg2+), in which the EPSFP is mediated primarily by non-NMDA receptors, IC50 values correlated closely with the Ki values against kainate/AMPA obtained in oocyte experiments but were approximately 8-fold higher. Similarly, in slices superfused with nominally Mg(2+)-free medium, in which the EPSFP is amplified due to a relief of the Mg2+ block of NMDA receptors, IC50 values correlated closely with the Ki values against glycine/NMDA obtained in oocyte experiments but were 60-fold higher. This comparison of results from the two experimental systems lends further support to the argument that hippocampal synaptic transmission is mediated postsynaptically by kainate/AMPA-type and NMDA/glycine-type EAA receptors that are pharmacologically indistinguishable from those expressed in mRNA-injected Xenopus oocytes. Furthermore, it suggests that EAA receptors in situ may be nearly saturated by high local concentrations of the endogenous ligands, a condition that would contribute substantially to the apparent non-NMDA receptor selectivity of certain quinoxaline derivatives.
Mol Pharmacol 1992 Feb
PMID:Quinoxaline derivatives: structure-activity relationships and physiological implications of inhibition of N-methyl-D-aspartate and non-N-methyl-D-aspartate receptor-mediated currents and synaptic potentials. 137 83

The endogenous neurotransmitter candidates L-aspartate, L-cysteine sulfinate (CSA), L-glutamate, L-homocysteate (HCA), and the endogenously occurring analogue quinolinate were compared in terms of potency, maximal activity, and selectivity for steady state activation of N-methyl-D-aspartate (NMDA) and non-NMDA [(RS)-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)] types of glutamate receptors expressed in Xenopus oocytes injected with mRNA isolated from rat brain (minus cerebellum). Selective activation of NMDA receptors was achieved by deleting Mg2+ and including 3-10 microM glycine in the perfusion medium and by applying ligands in the presence of 30 microM quisqualate, which blocks the AMPA receptor and desensitizes the oocyte's own Ca(2+)-dependent Cl- current. Oocytes were voltage clamped, and steady state inward currents were measured in response to perfusion with agonists at known concentrations. Under the NMDA receptor-preferring condition, the potency rank order was L-glutamate (EC50 = 2.2 microM, 95% confidence interval = 1.4-3.6 microM) greater than L-aspartate (13 microM) = HCA (13 microM) greater than CSA (59 microM) greater than quinolinate (greater than or equal to 7200 microM). All amino acids tested evoked similar maximal currents, which were 120-159% that of NMDA itself. The Hill coefficient was greater than 1 for all agonists except L-HCA (0.6), which might reflect heterogeneity of NMDA receptors expressed. This was supported by the finding that glycine was more potent in combination with HCA than NMDA, in activating NMDA receptors. To study the activity of agonists at AMPA receptors, glycine and quisqualate were omitted and 1 mM Mg2+ was included to block NMDA receptors. Ca(2+)-dependent Cl- currents activated by L-glutamate were prevented by inclusion of 0.4 M ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid in the recording electrode. All amino acids were less potent at AMPA receptors than at NMDA receptors; the potency rank order for steady state activation of AMPA receptors was L-glutamate (EC50 = 11 microM, 95% confidence interval = 7.3-18 microM) greater than HCA (430 microM) greater than CSA (3300 microM). L-Aspartate and quinolinate produced little or no inward current even up to 10 mM, i.e., were inactive at forebrain AMPA receptors. The maximal currents activated by all amino acids at steady state were 5-10% that of kainate, presumably due to severe desensitization of the AMPA receptor by the natural agonists. These results are consistent with L-glutamate acting as a mixed agonist at both AMPA and NMDA synaptic receptors and L-aspartate being involved exclusively in NMDA receptor-mediated synapses.
Mol Pharmacol 1992 Mar
PMID:Selectivity of amino acid transmitters acting at N-methyl-D-aspartate and amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptors. 137 86

Arcaine, a putative competitive antagonist at the polyamine site on the N-methyl-D-aspartate (NMDA) receptor complex, not only inhibits polyamine enhancement of NMDA-induced [3H]dizocilpine (MK-801) binding but also depresses binding in the absence of polyamines. In the present experiments, we investigated the mechanism of this latter effect in whole-cell and single-channel recordings from cultured rat hippocampal neurons. Arcaine produced a concentration-dependent block of NMDA-evoked inward currents (KD, 61 microM at -60 mV) but not those induced by kainate, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, or gamma-aminobutyric acid. The arcaine block was strongly voltage dependent and was almost completely relieved at positive holding potentials. Analysis of the voltage dependence indicated that the arcaine acceptor site appeared to sense 67% of the transmembrane electric field. In support of an open channel blocking mechanism, arcaine, like Mg2+, prevented dizocilpine from blocking the NMDA receptor channel. Moreover, increasing the dizocilpine concentration partially overcame the arcaine effect, indicating a competitive interaction between arcaine and dizocilpine. Spermine, which in our preparation usually produced only an arcaine-like voltage-dependent block of NMDA currents at high concentrations (greater than 100 microM), had no effect on the block by arcaine at lower concentrations. In single-channel recordings, arcaine caused a concentration- and voltage-dependent decrease in apparent channel amplitude. Assuming a simple model of open channel block, we estimate the arcaine binding and unbinding rates as 4.4 x 10(8) M-1 sec-1 and 1.8 x 10(4) sec-1, respectively, which are comparable to the rates for open channel block by Zn2+ and substantially faster than those of Mg2+. These results indicate that arcaine inhibits NMDA-induced [3H]dizocilpine binding by blocking the open NMDA receptor channel, an action that is independent of the polyamine site.
Mol Pharmacol 1992 Apr
PMID:Arcaine blocks N-methyl-D-aspartate receptor responses by an open channel mechanism: whole-cell and single-channel recording studies in cultured hippocampal neurons. 137 1

The glycine site on the N-methyl-D-aspartate (NMDA) subtype of receptors for the excitatory neurotransmitter glutamate is a potential target for the development of neuroprotective drugs. We report here two chemical series of glycine site antagonists derived from kynurenic acid (KYNA), with greatly improved potency and selectivity. Disubstitution with chlorine or bromine in the 5- and 7-positions of KYNA increased affinity for [3H]glycine binding sites in rat cortex/hippocampus P2 membranes, with a parallel increase of potency for antagonism of NMDA-evoked responses in the rat cortical wedge preparation. The optimal compound was 5-I,7-Cl-KYNA, with an IC50 for [3H]glycine binding of 29 nM and an apparent Kb in the cortical wedge preparation of 0.41 microM. Reduction of the right-hand ring of 5,7-diCl-KYNA reduced affinity by 10-fold, but this was restored by substitution in the 4-position with the trans-phenylamide and further improved in the trans-benzylamide. The optimal compound was the transphenylurea (L-689,560), with an IC50 of 7.4 nM and an apparent Kb of 0.13 microM. Both series of compounds displayed a high degree of selectivity for the glycine site, having IC50 values of greater than 10 microM versus radioligand binding to the glutamate recognition sites of NMDA, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA), and kainate receptors and the strychnine-sensitive glycine receptor. Selectivity versus AMPA receptor-mediated responses was also apparent in the rat cortical wedge and in patch-clamp recordings of cortical neurons in culture. Experiments using [3H]dizocilpine (MK-801) binding indicated that 5,7-diBr-KYNA, 5,7-diCl-KYNA, 5-I,7-Cl-KYNA, and L-689,560 all behaved as full antagonists and were competitive with glycine. Patch-clamp recordings of cortical neurons in culture also indicated that NMDA-induced currents were antagonized by competition for the glycine site, and gave no evidence for partial agonist activity. pKi values for 5,7-diBr-KYNA and L-689,560 in these experiments were 7.2 and 7.98, respectively, similar to the affinities of these compounds in the glycine binding assay. The high affinity and selectivity of these new derivatives make them useful tools to investigate the function of the glycine site on the NMDA receptor.
Mol Pharmacol 1992 May
PMID:Kynurenic acid analogues with improved affinity and selectivity for the glycine site on the N-methyl-D-aspartate receptor from rat brain. 137 17

Several polyamines have been shown to interact with a site on the N-methyl-D-aspartate (NMDA) receptor that regulates the binding of open channel blockers. Spermine (SP) and spermidine (SD), polyamine agonists, enhanced binding of open channel blockers, whereas arcaine (ARC), diethylenetriamine (DET), and putrescine (PUT), polyamine antagonists, reduced the polyamine enhancement of open channel blocker binding. We previously showed that SP had multiple actions on NMDA receptor single-channel currents that underlie its effect on whole-cell NMDA receptor current. At high concentrations, SP produced a voltage-dependent decrease in NMDA receptor single-channel conductance and average open time. In the present study, another polyamine agonist (SD) produced a similar reduction of NMDA receptor single-channel conductance at higher concentrations. The polyamine antagonists (ARC, DET, and PUT), however, produced a voltage-dependent reduction in NMDA receptor whole-cell currents and reductions in single-channel conductance and average open time, even in the absence of polyamine agonists. The rank order of potency for reduction of NMDA receptor single-channel conductance by polyamines was ARC greater than SP greater than SD greater than PUT = DET, a rank order similar to that for the inhibitory actions of polyamines in receptor binding assays and for the effects of the antagonists on NMDA receptor whole-cell currents. The polyamine antagonist DET did not block the reduction of single-channel conductance by the polyamine agonist SP. In fact, the effects of SP and DET on single-channel conductance were additive. DET also showed a variable enhancement of NMDA receptor whole-cell currents in some neurons, suggesting polyamine agonist-like properties. These results are not consistent with the standard pharmacological profile for agonists and antagonists acting at the same site. Potential mechanisms for the effects of the polyamines on single-channel conductance are discussed.
Mol Pharmacol 1992 Jul
PMID:Spermine and related polyamines produce a voltage-dependent reduction of N-methyl-D-aspartate receptor single-channel conductance. 137 23

In the present study, a relationship between convulsant activity and two cellular events, changes in calmodulin (CaM) concentration and proto-oncogene c-fos expression has been considered. c-fos has been found activated after the administration of the organochlorine insecticide lindane, the Ca2+ channel agonist Bay K, and N-methyl-D-aspartate (NMDA). The administration of the voltage-dependent Ca2+ channel antagonist nifedipine was able to block the expression elicited by lindane. The effect of lindane on c-fos expression could not be blocked by prior administration of MK-801, a non-competitive antagonist of the NMDA receptor. These results suggest a possible role for the voltage-dependent Ca2+ channels in the mechanism of action of lindane. By means of in situ hybridization, the different patterns of c-fos expression after the administration of the mentioned compounds have been described. A possible modification of the levels of CaM has also been investigated. Among all the subcellular fractions considered, only levels of nuclear CaM appeared to be affected after the different treatments. The changes observed seemed to follow a similar pattern to that described for c-fos induction. Calcium entry through these voltage-dependent calcium channels would be the link between membrane depolarizing events and expression of c-fos and/or increase in nuclear CaM.
Brain Res Mol Brain Res 1992 Aug
PMID:Effect of different convulsants on calmodulin levels and proto-oncogene c-fos expression in the central nervous system. 138 76

Structure-activity analysis reveals that acidic alpha-amino acids containing an omega-PO3H2 group are more potent antagonists at N-methyl-D-aspartate (NMDA) receptors than are analogs with omega-COOH or omega-tetrazole groups. At physiological values of extra-cellular pH the omega-PO3H2 group is only partially deprotonated and the corresponding antagonists exist as ions with one or two negative charges. In contrast, competitive antagonists with omega-COOH and omega-tetrazole groups are fully ionized at physiological pH but carry only a single negative charge. Dose-inhibition analysis was performed with (2R)-AP7 and its piperidine derivative LY 257883 to determine whether ionization of the omega-PO3H2 group influences NMDA receptor antagonist potency; these experiments revealed a > 3-fold increase in potency on raising of the extracellular pH from 7.3 to pH 8.2, consistent with the increase in the relative concentration of the ionic form of the antagonist in which the omega-PO3H2 group contains two negative charges. Experiments with the omega-COOH-containing analog of LY 257883 and with SDZ EAB 515, an omega-PO3H2-containing antagonist of novel structure, revealed only 1.5- and 1.3-fold increases in potency, respectively, over the same pH range. Analysis of the kinetics of block of NMDA-activated currents resulting from rapid application of LY 257883 suggests that the increase in potency on raising of the extracellular pH results largely from an increase in the antagonist association rate constant but also from a small decrease in the dissociation rate constant. Together, these results suggest that the fully ionized forms of the R-enantiomers of AP7 and LY 257883 act as the active antagonist species at NMDA receptors.
Mol Pharmacol 1992 Oct
PMID:Effect of extracellular pH on the potency of N-methyl-D-aspartic acid receptor competitive antagonists. 143 43

Several competitive antagonists of the N-methyl-D-aspartate (NMDA) subtype of excitatory amino acid receptors are phosphonate analogs of L-glutamic acid. The position of the phosphonate has been shown to be important in the structure-activity relationships of these analogs. To investigate whether other phosphorous-containing compounds had activity at the NMDA receptor, several organophosphates were tested for the ability to inhibit the specific binding to brain synaptic membranes of 3-((+-)-2-carboxypiperazin-4-yl)-[1,2-3H]propyl-1-phosphonic acid ([3H]CPP), a selective antagonist of NMDA receptors. Diisopropylfluorophosphate (DFP), dichlorvos, cyanophos, mipafox, and o-ethyl o-4-nitrophenyl phenylphosphonothioate are relatively potent inhibitors of [3H]CPP binding to synaptic membranes. The inhibition produced by DFP is selective for the NMDA subtype of excitatory amino acid receptors, is irreversible, and can be prevented by preincubation with excess CPP, 2-amino-7-phosphonoheptanoic acid, or L-glutamate. Rat brain synaptic membranes have a population of phosphonate-sensitive [3H]DFP binding sites that are covalently labeled by [3H]DFP. Two protein bands of synaptic membrane proteins subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis are labeled by [3H]DFP in a 2-amino-5-phosphonopentanoic acid-sensitive manner. These proteins have an average molecular size of 47-50 and 32 kDa. Proteins of nearly identical molecular sizes have been shown in other studies to be components of an NMDA receptor complex. These observations are indicative of an interaction between the organophosphates and the NMDA receptor protein complex and suggest that DFP may be another important pharmacological tool that can be used in the elucidation of the molecular structure of the NMDA receptor complex.
Mol Pharmacol 1992 Apr
PMID:Characterization of organophosphate interactions at N-methyl-D-aspartate receptors in brain synaptic membranes. 153 69


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