Wang S-J, Wang K-Y, Wang W-C
School of Medicine, Fu Jen Catholic University, 510 Chung-Cheng Road, Hsin-Chuang, Taipei Hsien, Taiwan 24205.
Neuroscience. 2004;125(1):191-201. doi: 10.1016/j.neuroscience.2004.01.019.
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 omega-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.
我们使用在线酶联荧光测定法，研究了具有抗惊厥特性的神经保护剂利鲁唑对大鼠脑皮质突触体释放内源性谷氨酸的影响。利鲁唑抑制了将脑皮质突触体暴露于钾通道阻滞剂4-氨基吡啶所诱发的谷氨酸钙依赖性释放，且这种突触前抑制呈浓度依赖性。利鲁唑既不改变4-氨基吡啶诱发的突触体膜电位去极化，也不改变离子霉素介导的谷氨酸释放，这表明利鲁唑介导的谷氨酸释放抑制并非由于突触体兴奋性降低或对胞吐机制的直接作用。对利鲁唑对Ca2+内流影响的研究表明，谷氨酸释放的减少可归因于胞质钙的降低。在用P/Q型钙通道阻滞剂ω-芋螺毒素IVA预处理突触体的实验中，证实了利鲁唑对突触体钙通道可能的作用，该预处理消除了利鲁唑介导的谷氨酸释放抑制。此外，用Gi/Go蛋白抑制剂百日咳毒素或GABAB受体激动剂巴氯芬预处理突触体，完全阻止了利鲁唑对4-氨基吡啶诱发的谷氨酸释放的抑制作用。得出的结论是，利鲁唑可能通过减少由P/Q型钙通道介导的钙内流发挥其突触前抑制作用，从而抑制大鼠脑皮质神经末梢谷氨酸的释放。这种释放抑制可能涉及百日咳毒素敏感的G蛋白信号通路。这一发现进一步支持了突触前钙通道阻滞与谷氨酸释放抑制同时发生可能是该药物治疗作用的重要机制这一观点。
