Lappaconitine inhibits glutamate release from rat cerebrocortical nerve terminals by suppressing Ca2+ influx and protein kinase A cascade

The inhibition of the excessive release of glutamate in the brain has emerged as a promising new option for developing therapeutic strategies for neurodegenerative disorders. This study investigated the effect and mechanism of lappaconitine, a diterpenoid alkaloid found in species of Aconitum , on glutamate release in rat cerebral cortex nerve terminals (synaptosomes). Here, we report that in the rat cortical synaptosomal preparation, lappaconitine reduced the K + channel blocker 4-aminopyridine (4-AP)-evoked Ca 2+ -dependent release of glutamate. The inhibitory effect of lappaconitine on the evoked glutamate release was blocked by the vesicular transporter inhibitor bafilomycin A1 and calcium-chelating agent ethylene glycol tetraacetic acid (EGTA), but was unaffected by exposure to the glutamate transporter inhibitor dl -threo-beta-benzyloxyaspartate ( dl -TBOA). The depolarization-induced elevation of cytosolic calcium concentration ([Ca 2+ ]c) was inhibited by lappaconitine, while the 4-AP-mediated depolarization of the synaptosomal membrane potential was not affected. The inhibition of glutamate release by lappaconitine was markedly decreased in synaptosomes pretreated with the Ca v 2.3 (R-type) channel blocker SNX-482 or the protein kinase A inhibitor H89. Nevertheless, the lappaconitine-mediated inhibition of glutamate release was not abolished by the intracellular Ca 2+ -release inhibitors dantrolene and CGP37157. Lappaconitine also significantly decreased the 4-AP-induced phosphorylation of PKA and SNAP-25, a presynaptic substrate for PKA. Our data suggest that lappaconitine reduces Ca 2+ influx through R-type Ca 2+ channels, subsequently reducing the protein kinase A cascade to inhibit the evoked glutamate release from rat cerebral cortex nerve terminals. • Lappaconitine inhibits glutamate release via calcium-dependent exocytosis. • Reduced Ca 2+ influx through Ca v 2.3 channels is involved. • This inhibitory effect depends on the suppression of the protein kinase A pathway. • Lappaconitine is a promising candidate for treating glutamate-induced excitotoxicity.