scholarly journals Rat cortical synaptosomes have more than one mechanism for Ca2+ entry linked to rapid glutamate release: studies using the Phoneutria nigriventer toxin PhTX2 and potassium depolarization

1993 ◽  
Vol 296 (2) ◽  
pp. 313-319 ◽  
Author(s):  
M A Romano-Silva ◽  
R Ribeiro-Santos ◽  
A M Ribeiro ◽  
M V Gomez ◽  
C R Diniz ◽  
...  
Keyword(s):  
Slow Component ◽  
Glutamate Uptake ◽  
Glutamate Release ◽  
South American ◽  
Potassium Depolarization ◽  
Additional Increase ◽  
Agelenopsis Aperta ◽  
Release Studies ◽  
Dose Dependent ◽  
Phoneutria Nigriventer

PhTX2, one of the components of the venom of the South American spider Phoneutria nigriventer, inhibits the closure of voltage-sensitive Na+ channels. Incubation of cerebral-cortical synaptosomes with PhTX2 causes a rapid increase in the intrasynaptosomal free Ca2+ concentration and a dose-dependent release of glutamate. This release is made up of a slow component, which appears to be due to reversal of Na(+)-dependent glutamate uptake, and more rapid component that is dependent on the entry of extrasynaptosomal Ca2+. It has previously been shown that membrane depolarization using KCl can cause rapid Ca(2+)-dependent release of glutamate from synaptosomes. This requires Ca2+ entry through a specific type of Ca2+ channel that is sensitive to Aga-GI, a toxic component of the venom of the spider Agelenopsis aperta. We have compared the effects of PhTX2 and KCl on elevation of intrasynaptosomal free Ca2+ and glutamate release, and a number of differences have emerged. Firstly, PhTX2-mediated Ca2+ influx and glutamate release, but not those caused by KCl, are inhibited by tetrodotoxin. Secondly, KCl produces a clear additional increase in Ca2+ and glutamate release following those elicited by PhTX2. Finally, 500 microM MnCl2 abolishes PhTX2-mediated, but not KCl-mediated, glutamate release. These findings suggest that more than one mechanism of Ca2+ entry may be coupled to glutamate release from nerve endings.

scholarly journals Inhibition of glutamate uptake by a polypeptide toxin (phoneutriatoxin 3-4) from the spider Phoneutria nigriventer

1999 ◽  
Vol 343 (2) ◽  
pp. 413-418 ◽  
Author(s):  
Helton J. REIS ◽  
Marco A. M. PRADO ◽  
Evanguedes KALAPOTHAKIS ◽  
Marta N. CORDEIRO ◽  
Carlos R. DINIZ ◽  
...  
Keyword(s):  
Glutamate Uptake ◽  
Glutamate Release ◽  
Dependent Manner ◽  
Glutamatergic Neurotransmission ◽  
Brain Ischaemia ◽  
Glutamate Concentration ◽  
Extracellular Compartment ◽  
Voltage Dependent ◽  
Ca2 Channels ◽  
Phoneutria Nigriventer

Glutamate concentration increases significantly in the extracellular compartment during brain ischaemia and anoxia. This increase has an important Ca2+-independent component, which is due in part to the reversal of glutamate transporters of the plasma membrane of neurons and glia. The toxin phoneutriatoxin 3-4 (Tx3-4) from the spider Phoneutria nigriventer has been reported to decrease the evoked glutamate release from synaptosomes by inhibiting Ca2+ entry via voltage-dependent Ca2+ channels. However, we report here that Tx3-4 is also able to inhibit the uptake of glutamate by synaptosomes in a time-dependent manner and that this inhibition in turn leads to a decrease in the Ca2+-independent release of glutamate. No other polypeptide toxin so far described has this effect. Our results suggest that Tx3-4 can be a valuable tool in the investigation of function and dysfunction of glutamatergic neurotransmission in diseases such as ischaemia.

Presynaptic Modulation of Synaptic Transmission by Pregnenolone Sulfate as Studied by Optical Recordings

2005 ◽  
Vol 94 (6) ◽  
pp. 4131-4144 ◽  
Author(s):  
Ling Chen ◽  
Masahiro Sokabe
Keyword(s):  
Synaptic Transmission ◽  
Glutamate Release ◽  
Hippocampal Slices ◽  
Receptor Activation ◽  
Optical Recording ◽  
Perforant Path ◽  
Dependent Manner ◽  
Pregnenolone Sulfate ◽  
Voltage Sensitive Dyes ◽  
Dose Dependent

The effects of pregnenolone sulfate (PREGS), a putative neurosteroid, on the transmission of perforant path–granule cell synapses were investigated with an optical recording technique in rat hippocampal slices stained with voltage-sensitive dyes. Application of PREGS to the bath solution resulted in an acute augmentation of EPSP in a dose-dependent manner. The PREGS effect was dependent on the extracellular Ca2+ concentration ([Ca2+]o), but independent of NMDA receptor activation. PREGS caused a decrease in paired-pulse facilitation, which implies that PREGS positively modulates presynaptic neurotransmitter releases. Firmer support for this mechanism was that PREGS augmented the synaptically induced glial depolarization (SIGD) that reflects the activity of electrogenic glutamate transporters in glial cells during the uptake of released glutamate. The selective α7nAChR antagonist α-BGT or MLA prevented the SIGD increase by PREGS. Furthermore DMXB, a selective α7nAChR agonist, mimicked the PREGS effect on SIGD and antagonized the effect of PREGS. The presynaptic effect of PREGS was partially attenuated by the L-type Ca2+ channel (VGCC) blocker nifedipine. Based on these findings, we proposed a novel mechanism underlying the facilitated synaptic transmission by PREGS: this neurosteroid sensitizes presynaptic α7nAChR that is followed by an activation of L-type VGCC to increase the presynaptic glutamate release.

scholarly journals Ischemic Preconditioning Reveals that GLT1/EAAT2 Glutamate Transporter is a Novel PPARγ Target Gene Involved in Neuroprotection

2007 ◽  
Vol 27 (7) ◽  
pp. 1327-1338 ◽  
Author(s):  
Cristina Romera ◽  
Olivia Hurtado ◽  
Judith Mallolas ◽  
Marta P Pereira ◽  
Jesús R Morales ◽  
...  
Keyword(s):  
Nervous System ◽  
Ischemic Preconditioning ◽  
Transcriptional Activity ◽  
Target Gene ◽  
Glutamate Uptake ◽  
Glutamate Release ◽  
Glutamate Transporter ◽  
Glutamate Transport ◽  
Extracellular Glutamate ◽  
Pparγ Agonist

Excessive levels of extracellular glutamate in the nervous system are excitotoxic and lead to neuronal death. Glutamate transport, mainly by glutamate transporter GLT1/EAAT2, is the only mechanism for maintaining extracellular glutamate concentrations below excitotoxic levels in the central nervous system. We recently showed that neuroprotection after experimental ischemic preconditioning (IPC) involves, at least partly, the upregulation of the GLT1/EAAT2 glutamate transporter in astrocytes, but the mechanisms were unknown. Thus, we decided to explore whether activation of the nuclear receptor peroxisome proliferator-activated receptor (PPAR)γ, known for its antidiabetic and antiinflammatory properties, is involved in glutamate transport. First, we found that the PPARγ antagonist T0070907 inhibits both IPC-induced tolerance and reduction of glutamate release after lethal oxygen-glucose deprivation (OGD) (70.1% ± 3.4% versus 97.7% ± 5.2% of OGD-induced lactate dehydrogenase (LDH) release and 61.8% ± 5.9% versus 85.9% ± 7.9% of OGD-induced glutamate release in IPC and IPC + T0070907 1 μmol/L, respectively, n = 6 to 12, P < 0.05), as well as IPC-induced astrocytic GLT-1 overexpression. IPC also caused an increase in nuclear PPARγ transcriptional activity in neurons and astrocytes (122.1% ± 8.1% and 158.6% ± 22.6% of control PPARγ transcriptional activity, n = 6, P < 0.05). Second, the PPARγ agonist rosiglitazone increased both GLT-1/EAAT2 mRNA and protein expression and [3H]glutamate uptake, and reduced OGD-induced cell death and glutamate release (76.3% ± 7.9% and 65.5% ± 15.1% of OGD-induced LDH and glutamate release in rosiglitazone 1 μmol/l, respectively, n = 6 to 12, P < 0.05). Finally, we have identified six putative PPAR response elements (PPREs) in the GLT1/EAAT2 promoter and, consistently, rosiglitazone increased fourfold GLT1/EAAT2 promoter activity. All these data show that the GLT1/EAAT2 glutamate transporter is a target gene of PPARγ leading to neuroprotection by increasing glutamate uptake.

scholarly journals NLRX1 Enhances Glutamate Uptake and Inhibits Glutamate Release by Astrocytes

Cells ◽  
2019 ◽  
Vol 8 (5) ◽  
pp. 400 ◽  
Author(s):  
Shaimaa Mahmoud ◽  
Marjan Gharagozloo ◽  
Camille Simard ◽  
Abdelaziz Amrani ◽  
Denis Gris
Keyword(s):  
Glutamate Uptake ◽  
Glutamate Release ◽  
Neuronal Firing ◽  
Glutamate Excitotoxicity ◽  
Cns Inflammation ◽  
Atp Production ◽  
Inflammatory Conditions ◽  
Mitochondrial Functions ◽  
The Central Nervous System ◽  
First Time

Uptake of glutamate from the extracellular space and glutamate release to neurons are two major processes conducted by astrocytes in the central nervous system (CNS) that protect against glutamate excitotoxicity and strengthen neuronal firing, respectively. During inflammatory conditions in the CNS, astrocytes may lose one or both of these functions, resulting in accumulation of the extracellular glutamate, which eventually leads to excitotoxic neuronal death, which in turn worsens the CNS inflammation. NLRX1 is an innate immune NOD-like receptor that inhibits the major inflammatory pathways. It is localized in the mitochondria and was shown to inhibit cell death, enhance ATP production, and dampen oxidative stress. In the current work, using primary murine astrocyte cultures from WT and Nlrx1-/- mice, we demonstrate that NLRX1 potentiates astrocytic glutamate uptake by enhancing mitochondrial functions and the functional activity of glutamate transporters. Also, we report that NLRX1 inhibits glutamate release from astrocytes by repressing Ca2+-mediated glutamate exocytosis. Our study, for the first time, identified NLRX1 as a potential regulator of glutamate homeostasis in the CNS.

Neuroprotective Effects of Propofol in a Model of Ischemic Cortical Cell Cultures

2003 ◽  
Vol 99 (2) ◽  
pp. 368-375 ◽  
Author(s):  
Lionel J. Velly ◽  
Benjamin A. Guillet ◽  
Frederique M. Masmejean ◽  
André L. Nieoullon ◽  
Nicolas J. Bruder ◽  
...  
Keyword(s):  
Lactate Dehydrogenase ◽  
Cell Cultures ◽  
Glutamate Uptake ◽  
Neuroprotective Effect ◽  
Glutamate Release ◽  
Cortical Cell ◽  
Neuroprotective Effects ◽  
Mk 801 ◽  
Lactate Dehydrogenase Release ◽  
Cortical Cell Cultures

Background During cerebral ischemia, excess of glutamate release and dysfunction of its high affinity transport induce an accumulation of extracellular glutamate, which plays an important role in neuronal death. The authors studied the relationship among propofol neuroprotection, glutamate extracellular concentrations, and glutamate transporter activity in a model of ischemic cortical cell cultures. Methods Thirteen-day-old primary cortical neuronal-glial cultures were exposed to a 90-min combined oxygen-glucose deprivation (OGD) in an anaerobic chamber, followed by reoxygenation. Propofol was added only during the OGD period, and its effect was compared to that of the N-methyl-d-aspartate receptor antagonist dizocilpine (MK-801). Twenty-four hours after the injury, cell death was quantified by lactate dehydrogenase release and cell viability by reduction of 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT). Extracellular concentrations of glutamate in culture supernatants and glutamate uptake were performed at the end of OGD period by high-performance liquid chromatography and incorporation of l-[3H]glutamate into cells, respectively. Results At clinically relevant concentrations (0.05-10 microm), propofol offered protection equivalent to that of MK-801. It significantly reduced lactate dehydrogenase release and increased the reduction of MTT. At the end of the ischemic injury, propofol was able to reverse the OGD-induced increase in glutamate extracellular concentrations and decrease of glutamate uptake. The inhibition of the glial GLT1 transporter by 3-methyl-glutamate did not further modify the effect of propofol on glutamate uptake, suggesting that GLT1 was not the major target of propofol. Conclusion Propofol showed a neuroprotective effect in this in vitro model of OGD, which was apparently mediated by a GLT1-independent restoration of the glutamate uptake impaired during the injury.

Ischemia But Not Anoxia Evokes Vesicular and Ca2+-Independent Glutamate Release In the Dorsal Vagal Complex In Vitro

2000 ◽  
Vol 83 (5) ◽  
pp. 2905-2915 ◽  
Author(s):  
Anna Kulik ◽  
Stefan Trapp ◽  
Klaus Ballanyi
Keyword(s):  
Glutamate Uptake ◽  
Glutamate Release ◽  
Outward Current ◽  
Cyclopiazonic Acid ◽  
Synaptic Activity ◽  
Dorsal Vagal Complex ◽  
Free Solution ◽  
Inward Current ◽  
Metabolic Arrest

Whole cell recordings of fura-2 dialyzed vagal neurons of brain stem slices were used to monitor interstitial glutamate accumulation within the dorsal vagal complex. Anoxia produced a sustained outward current (60 pA) and a moderate [Ca2+]i rise (40 nM). These responses were neither mimicked by [1S,3R]-1-aminocyclo-pentane-1,3-dicarboxylic acid nor affected by Ca2+-free solution, 6-cyano-7-nitroquino-xaline-2,3-dione (CNQX), 2-amino-5-phosphonovalerate (APV), or tetrodotoxin. Anoxia or cyanide in glucose-free saline (in vitro ischemia) as well as ouabain or iodoacetate elicited an initial anoxia-like [Ca2+]i increase that turned after several minutes into a prominent Ca2+ transient (0.9 μM) and inward current (−1.8 nA). APV plus CNQX (plus methoxyverapamil) inhibited this inward current as well as accompanying spontaneous synaptic activity, and reduced the secondary [Ca2+]i rise to values similar to those during anoxia. Each of the latter drugs delayed onset of both ischemic current and prominent [Ca2+]i rise by several minutes and attenuated their magnitudes by up to 40%. Ca2+-free solution induced a twofold delay of the ischemic inward current and suppressed the prominent Ca2+ increase but not the initial moderate [Ca2+]i rise. Cyclopiazonic acid or arachidonic acid in Ca2+-free saline delayed further the ischemic current, whereas neither inhibitors of glutamate uptake (dihydrokainate,d,l-threo-β-hydroxyaspartate,l-transpyrrolidone-2,4-dicarboxylate) nor the Cl− channel blocker 5-nitro-2-(3-phenylpropyl-amino) benzoic acid had any effect. In summary, the response to metabolic arrest is due to activation of ionotropic glutamate receptors causing Ca2+ entry via N-methyl-d-aspartate receptors and voltage-activated Ca2+ channels. An early Ca2+-dependent exocytotic phase of ischemic glutamate release is followed by nonvesicular release, not mediated by reversed glutamate uptake or Cl− channels. The results also show that glycolysis prevents glutamate release during anoxia.

Involvement of glutamate in ischemic neurodegeneration in isolated retina

2003 ◽  
Vol 20 (2) ◽  
pp. 97-107 ◽  
Author(s):  
YUKITOSHI IZUMI ◽  
SETH B. HAMMERMAN ◽  
CHARITY O. KIRBY ◽  
ANN M. BENZ ◽  
JOHN W. OLNEY ◽  
...  
Keyword(s):  
Glutamate Receptors ◽  
Ex Vivo ◽  
Glutamate Uptake ◽  
Glutamate Release ◽  
Plexiform Layer ◽  
Cell Swelling ◽  
Inner Plexiform Layer ◽  
Simulated Ischemia ◽  
High Concentrations ◽  
Bull's Eye

Retinal ischemia, a major cause of visual loss, is believed to result from overexcitation of glutamate receptors. However, under euglycemic and normoxic conditions, exogenously applied glutamate is not neurotoxic in the retina. Under such conditions, exogenous glutamate typically causes glia swelling and requires very high concentrations to produce neurotoxicity. To determine whether ischemic conditions enhance the neurotoxicity of endogenous and exogenous glutamate, we examined the effects of simulated ischemia (deprivation of both glucose and oxygen) on retinal morphology and lactate dehydrogenase (LDH) release. In an ex vivo rat retinal preparation, glutamate was administered during simulated ischemia in the presence of riluzole, an inhibitor of glutamate release. Deprivation of both glucose and oxygen for 60 min at 30°C produced severe acute neurodegeneration. This neurodegeneration, characterized by bull's eye formation in the inner nuclear layer and spongy appearance in the inner plexiform layer, was prevented by the combination of MK-801 and DNQX, antagonists of N-methyl-D-aspartate (NMDA) and non-NMDA receptors, indicating that the damage results from activation of both glutamate receptors. We also found that administration of glutamate pyruvate transaminase (alanine aminotransaminase) with pyruvate diminished the neurodegeneration during simulated ischemia. Furthermore, riluzole, an inhibitor of glutamate release, attenuated the neurodegeneration, suggesting the importance of endogenous glutamate in ischemic damage. In the presence of riluzole and simulated ischemia, exogenously applied glutamate failed to cause Müller cell swelling but was extremely neurotoxic. These results suggest that simulated ischemia enhances glutamate-mediated neurotoxicity in part by depressing glutamate uptake. When glutamate transport is impaired, sub-millimolar glutamate concentrations become profoundly neurotoxic.

Platelet Glutamate Uptake and Release in Migraine With and Without Aura

Cephalalgia ◽  
2007 ◽  
Vol 27 (1) ◽  
pp. 35-40 ◽  
Author(s):  
M Vaccaro ◽  
C Riva ◽  
L Tremolizzo ◽  
M Longoni ◽  
A Aliprandi ◽  
...  
Keyword(s):  
Amino Acid ◽  
High Performance ◽  
Spreading Depression ◽  
Glutamate Uptake ◽  
Glutamate Release ◽  
Plasma Concentrations ◽  
Control Group ◽  
Therapeutic Approaches ◽  
The Brain ◽  
Uptake And Release

Glutamate may play an important role in the pathogenesis of migraine: glutamate release in the brain may be involved in the development of spreading depression and increased concentrations of this amino acid have been reported in plasma and platelets from migraine patients. Here we assessed platelet glutamate uptake and release in 25 patients affected by migraine with aura (MA) and 25 patients affected by migraine without aura (MoA), comparing the results with a group of 20 healthy matched controls. Both glutamate release from stimulated platelets and plasma concentrations of the amino acid were assessed by high-performance liquid chromatography, and were increased in both types of migraine, although more markedly in MA. Platelet glutamate uptake, assessed as 3H-glutamate intake, was increased in MA, while it was reduced in MoA with respect to the control group. These results support the view that MA might involve different pathophysiological mechanisms from MoA and, specifically, up-regulation of the glutamatergic metabolism. Understanding these dysfunctional pathways could lead to new, possibly more successful therapeutic approaches to the management of migraine.

scholarly journals Benzoate stimulates glutamate release from perfused rat liver

1989 ◽  
Vol 264 (3) ◽  
pp. 837-843 ◽  
Author(s):  
D Häussinger ◽  
T Stehle ◽  
J P Colombo
Keyword(s):  
Rat Liver ◽  
Glutamate Release ◽  
Isolated Perfused Rat Liver ◽  
Perfused Rat Liver ◽  
Ammonia Metabolism ◽  
Ammonia Uptake ◽  
Glutamine Synthesis ◽  
Methionine Sulphoximine ◽  
Dose Dependent ◽  
Glutamate Efflux

In isolated perfused rat liver, benzoate addition to the influent perfusate led to a dose-dependent, rapid and reversible stimulation of glutamate output from the liver. This was accompanied by a decrease in glutamate and 2-oxoglutarate tissue levels and a net K+ release from the liver; withdrawal of benzoate was followed by re-uptake of K+. Benzoate-induced glutamate efflux from the liver was not dependent on the concentration (0-1 mM) of ammonia (NH3 + NH4+) in the influent perfusate, but was significantly increased after inhibition of glutamine synthetase by methionine sulphoximine or during the metabolism of added glutamine (5 mM). Maximal rates of benzoate-stimulated glutamate efflux were 0.8-0.9 mumol/min per g, and the effect of benzoate was half-maximal (K0.5) at 0.8 mM. Similar Vmax. values of glutamate efflux were obtained with 4-methyl-2-oxopentanoate, ketomethionine (4-methylthio-2-oxobutyrate) and phenylpyruvate; their respective K0.5 values were 1.2 mM, 3.0 mM and 3.8 mM. Benzoate decreased hepatic net ammonia uptake and synthesis of both urea and glutamine from added NH4Cl. Accordingly, the benzoate-induced shift of detoxication from urea and glutamine synthesis to glutamate formation and release was accompanied by a decreased hepatic ammonia uptake. The data show that benzoate exerts profound effects on hepatic glutamate and ammonia metabolism, providing a new insight into benzoate action in the treatment of hyperammonaemic syndromes.

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