Elsevier

Neuroscience

Volume 125, Issue 1, 2004, Pages 191-201
Neuroscience

Mechanisms underlying the riluzole inhibition of glutamate release from rat cerebral cortex nerve terminals (synaptosomes)

https://doi.org/10.1016/j.neuroscience.2004.01.019Get rights and content

Abstract

We have examined the effect of riluzole, a neuroprotective agent with anticonvulsant properties, on the release of endogenous glutamate from rat cerebrocortical synaptosomes using an on-line enzyme-coupled fluorometric assay. Riluzole inhibited the calcium-dependent release of glutamate that was evoked by exposing cerebrocortical synaptosomes to the potassium channel blocker 4-aminopyridine, and this presynaptic inhibition was concentration-dependent. Riluzole did not alter either 4-aminopyridine-evoked depolarization of the synaptosomal membrane potential or ionomycin-mediated glutamate release, indicating that riluzole-mediated inhibition of glutamate release is not due to a decrease in synaptosomal excitability or a direct effect on the exocytotic machinery. Examination of the effect of riluzole on Ca2+ influx revealed that the diminution of glutamate release could be attributed to a reduction in cytosolic calcium. A possible effect of riluzole on synaptosomal calcium channels was confirmed in experiments where synaptosomes pretreated with P/Q-type calcium channel blocker ω-agatoxin IVA, which abolished the riluzole-mediated inhibition of glutamate release. In addition, pretreatment of synaptosomes with either the Gi/Go protein inhibitor pertussis toxin or the GABAB receptor agonist baclofen, completely prevented the inhibitory effect of riluzole on 4-aminopyridine-evoked glutamate release.

It is concluded that riluzole exerts their presynaptic inhibition, likely through a reduction in the calcium influx mediated by P/Q-type calcium channels, and thereby inhibits the release of glutamate from rat cerebrocortical nerve terminals. This release inhibition may involve a pertussis toxin-sensitive G protein signalling pathway. This finding provides further support that presynaptic calcium channel blockade concomitant with inhibition of glutamate release could be an important mechanism underlying the therapeutic actions of this drug.

Section snippets

Materials

Fura-2-acetoxymethyl ester and DiSC3(5) were obtained from Molecular Probes (Eugene, OR, USA). Percoll was obtained from Pharmacia. Riluzole was obtained from Tocris Cookson (Bristol, USA). Glutamate dehydrogenase and all other reagents were obtained from Sigma (Poole, UK) or Merck (Poole, UK).

Synaptosomal preparation

Synaptosomes were purified as described previously (Sihra, 1997). Briefly, the cerebral cortex from 2-month-old male Sprague–Dawley rats was isolated and homogenised in a medium containing 320 mM sucrose,

Results

Glutamate release from purified cerebrocortical synaptosomes was monitored on-line continuously using an assay employing exogenous GDH and NADP+ to couple the oxidative deamination of released glutamate to the generation of NADPH, which is detected fluorometrically (Nicholls et al., 1987). Under synaptosomes incubated in the presence of 1 mM CaCl2, the release of glutamate evoked by 3 mM 4AP, a potassium channel blocker that opens voltage-gated Ca2+ channels and induces the release of vesicular

Discussion

Riluzole is primarily used clinically in the treatment of ALS, where glutamate damage is considered as a major pathogenetic factor. Thus, it prompted us to focus on this neurotransmitter in the present study. The results of the present study demonstrate that riluzole inhibits glutamate release from rat cerebrocortical nerve terminals possibly by reducing Ca2+ influx through P/Q-type Ca2+ channels, and that the activation of a pertussis toxin-sensitive G protein is involved in this effect.

Acknowledgements

This work was supported by the National Science Council of Taiwan, Republic of China (NSC 92-2320-B-030-005).

References (53)

  • I.M. Mintz et al.

    P-type calcium channels in rat central and peripheral neurons

    Neuron

    (1992)
  • M. Prakriya et al.

    Selective depression of low-release probability excitatory synapses by sodium channel blockers

    Neuron

    (2000)
  • T.J. Rink et al.

    Lymphocyte membrane potential assessed with fluorescent probes

    Biochim Biophys Acta

    (1980)
  • J. Roeper et al.

    Presynaptic potassium channels

    Curr Opin Neurobiol

    (1996)
  • C. Rosenmund et al.

    Definition of the readily releasable pool of vesicles at hippocampal synapses

    Neuron

    (1996)
  • M. Scanziani et al.

    Presynaptic inhibition of miniature excitatory synaptic currents by baclofen and adenosine in the hippocampus

    Neuron

    (1992)
  • T.S. Sihra et al.

    Localized Ca2+ entry preferentially effects protein dephosphorylation, phosphorylation, and glutamate release

    J Biol Chem

    (1992)
  • A. Stefani et al.

    Differential inhibition by riluzole, lamotrigine, and phenytoin of sodium and calcium currents in cortical neuronsImplications for neuroprotective strategies

    Exp Neurol

    (1997)
  • T.J. Turner et al.

    Pharmacological characterization of presynaptic calcium channels using subsecond biochemical measurements of synaptosomal neurosecretion

    Neuropharmacology

    (1995)
  • S.J. Wang

    Cannabinoid CB1 receptor-mediated inhibition of glutamate release from rat hippocampal synaptosomes

    Eur J Pharmacol

    (2003)
  • J. Wokke

    Riluzole

    Lancet

    (1996)
  • X.Z. Zhu et al.

    Modulation of calcium uptake and d-aspartate release by BABAB receptors in culture cerebellar granule cells

    Eur J Pharmacol

    (1987)
  • C. Zona et al.

    Riluzole interacts with voltage-activated sodium and potassium currents in cultured rat cortical neurons

    Neuroscience

    (1998)
  • K.E. Akerman et al.

    Ionic dependence of membrane potential and glutamate receptor-linked responses in synaptoneurosomes as measured with a cyanine dye, DiS-C2-(5)

    J Neurochem

    (1987)
  • G. Bensimon et al.

    A controlled trial of riluzole in amyotrophic lateral sclerosisAls/riluzole study group

    N Engl J Med

    (1994)
  • T.V. Bliss et al.

    A synaptic model of memoryLong-term potentiation in the hippocampus

    Nature

    (1993)
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