title: Tanshinone IIA, a constituent of Danshen, inhibits the release of glutamate in rat cerebrocortical nerve terminals.
abstract: BACKGROUND
  Danshen 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.
  
  
  OBJECTIVE
  An 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.
  
  
  METHODS
  The 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 Ca(2+) indicator, Fura-2-acetoxymethyl ester, to monitor cytosolic Ca(2+) concentrations ([Ca(2+)]C).
  
  
  RESULTS
  Tanshinone 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 Ca(2+) 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 [Ca(2+)]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(+)/Ca(2+) exchanger blocker CGP37157. Mitogen-activated protein kinase (MEK) inhibition also prevented the inhibitory effect of tanshinone IIA on evoked glutamate release.
  
  
  CONCLUSIONS
  These results show that tanshinone IIA inhibits glutamate release from cortical synaptosomes in rats through the suppression of presynaptic voltage-dependent Ca(2+) entry and MEK signaling cascade.
authors.affiliation: Department of Anesthesiology, Far-Eastern Memorial Hospital, Pan-Chiao District, New Taipei City 22060, Taiwan.
authors.forename: Tzu Yu
authors.initials: TY
authors.lastname: Lin
authors.forename: Cheng Wei
authors.initials: CW
authors.lastname: Lu
authors.forename: Shu-Kuei
authors.initials: SK
authors.lastname: Huang
authors.forename: Su-Jane
authors.initials: SJ
authors.lastname: Wang
mesh_terms: D015761:4-Aminopyridine / Q000494:pharmacology; D045784:Abietanes / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000502:physiology; D002540:Cerebral Cortex / Q000166:cytology*; D004365:Drugs, Chinese Herbal; D018698:Glutamic Acid / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D026902:Potassium Channel Blockers / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D027561:Salvia miltiorrhiza; D013574:Synaptosomes / Q000378:metabolism*
chemical_list: D045784:Abietanes; D004365:Drugs, Chinese Herbal; D026902:Potassium Channel Blockers; C021751:tanshinone; D018698:Glutamic Acid; D015761:4-Aminopyridine; D020928:Mitogen-Activated Protein Kinases; D002118:Calcium