Tanshinone IIA, a constituent of Danshen, inhibits the release of glutamate in rat cerebrocortical nerve terminals

Abstract

Ethnopharmacological relevanceDanshen is a commonly used traditional Chinese medicine and has received considerable attention due to their beneficial effects on the health, including prevention of cardiovascular disease, and cancer. Tanshinone IIA, a major active constituent of Danshen, has been reported to have a neuroprotective profile. Aim of the studyAn excessive release of glutamate is considered to be related to neuropathology of several neurological diseases. In this study, we investigated whether tanshinone IIA could affect endogenous glutamate release and explored the possible mechanism. Materials and methodsThe experimental model was the isolated nerve terminals (synaptosomes) purified from the rat cerebral cortex. The release of glutamate was evoked by the K+ channel blocker 4-aminopyridine (4-AP) and measured by one-line enzyme-coupled fluorometric assay. We also used a membrane potential-sensitive dye to assay nerve terminal excitability and depolarization, and a Ca2+ indicator, Fura-2-acetoxymethyl ester, to monitor cytosolic Ca2+ concentrations ([Ca2+]C). ResultsTanshinone IIA inhibited the release of glutamate evoked by 4-AP in a concentration-dependent manner. Inhibition of glutamate release by tanshinone IIA was prevented by the chelating the extracellular Ca2+ ions, and by the vesicular transporter inhibitor bafilomycin A1. However, the glutamate transporter inhibitor DL-threo-beta-benzyl-oxyaspartate did not have any effect on the action of tanshinone IIA. Tanshinone IIA decreased the depolarization-induced increase in [Ca2+]C, whereas it did not alter the resting synaptosomal membrane potential or 4-AP-mediated depolarization. Furthermore, the effect of tanshinone IIA on evoked glutamate release was prevented by the Cav2.2 (N-type) and Cav2.1 (P/Q-type) channel blocker ω-conotoxin MVIIC, but not by the ryanodine receptor blocker dantrolene or the mitochondrial Na+/Ca2+ exchanger blocker CGP37157. Mitogen-activated protein kinase (MEK) inhibition also prevented the inhibitory effect of tanshinone IIA on evoked glutamate release. ConclusionThese results show that tanshinone IIA inhibits glutamate release from cortical synaptosomes in rats through the suppression of presynaptic voltage-dependent Ca2+ entry and MEK signaling cascade.