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Ginkgolide B, a constituent of Ginkgo biloba, facilitates glutamate exocytosis from rat hippocampal nerve terminals

Elsevier B.V.
Publication Date
DOI: 10.1016/j.ejphar.2005.03.027
  • Ginkgolide B
  • Glutamate Exocytosis
  • Hippocampal Synaptosome
  • Presynaptic Voltage-Dependent Ca2+Influx
  • Protein Kinase A
  • Biology
  • Medicine


Abstract Although previous studies have demonstrated that Ginkgo biloba extract has modest effects in the improvement of memory and cognitive function of the Alzheimer's disease patients, the mechanism(s) underlyling its beneficial effects remain(s) unclear. In this study, the effect of ginkgolide B, one of the major constituents of Ginkgo biloba extract, on the release of endogenous glutamate from rat hippocampal nerve terminals (synaptosomes) was studied. Ginkgolide B facilitated the Ca 2+-dependent release of glutamate evoked by 4-aminopyridine in a concentration-dependent manner. The facilitatory action of ginkgolide B was not due to it increasing synaptosomal excitability because ginkgolide B did not alter the 4-aminopyridine-evoked depolarization of the synaptosomal plasma membrane potential. Rather, examination of the effect of ginkgolide B on cytosolic free Ca 2+ concentration revealed that the facilitation of glutamate release could be attributed to an enhancement of presynaptic voltage-dependent Ca 2+ influx. Consistent with this, the ginkgolide B-mediated facilitation of glutamate release was significantly prevented in synaptosomes pretreated with a wide spectrum blocker of N-, P-, and Q-type Ca 2+ channels, ω-conotoxin MVIIC. Moreover, the facilitation produced by ginkgolide B was completely abolished by the protein kinase A inhibitor, but not by the protein kinase C inhibitor. These results suggest that ginkgolide B effects a increase in protein kinase A activation, which subsequently enhances the Ca 2+ entry through voltage-dependent N- and P/Q-type Ca 2+ channels to cause a increase in evoked glutamate release from rat hippocampal nerve terminals. In addition, glutamate release elicited by Ca 2+ ionophore (ionomycin) was also facilitated by ginkgolide B, which suggests that ginkgolide B may have a direct effect on the secretory apparatus downstream of Ca 2+ entry. These actions of ginkgolide B may provide some information regarding the beneficial effects of Ginkgo biloba in the central nervous system.

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