The excitotoxicity caused by excessive
glutamate is a critical
element in the neuropathology of acute and chronic
brain disorders. Therefore, inhibition of
glutamate release is a potentially valuable therapeutic strategy for treating these diseases. In this study, we investigated the effect of
celecoxib, a selective
cyclooxygenase-2 (COX-2) inhibitor that reduces the level of
prostaglandin E2 (
PGE2), on endogenous
glutamate release in rat cerebral cortex nerve terminals (synaptosomes).
Celecoxib substantially inhibited the release of
glutamate induced by the K(+) channel blocker
4-aminopyridine (4-AP), and this phenomenon was prevented by chelating the extracellular Ca(2+)
ions and by the vesicular transporter inhibitor
bafilomycin A1.
Celecoxib inhibited a 4-AP-induced increase in cytosolic-free Ca(2+) concentration, and the
celecoxib-mediated inhibition of
glutamate release was prevented by the Cav2.2 (N-type) and
Cav2.1 (P/Q-type) channel blocker ω-
conotoxin MVIIC. However,
celecoxib did not alter 4-AP-mediated depolarization and Na(+) influx. In addition, this
glutamate release-inhibiting effect of
celecoxib was mediated through the
PGE2 subtype 2 receptor (EP2) because it was not observed in the presence of
butaprost (an EP2 agonist) or PF04418948 [1-(4-fluorobenzoyl)-3-[[6-methoxy-2-naphthalenyl)methyl]-
3-azetidinecarboxylic acid; an EP2 antagonist]. The
celecoxib effect on 4-AP-induced
glutamate release was prevented by the inhibition or activation of
protein kinase A (PKA), and
celecoxib decreased the 4-AP-induced phosphorylation of PKA. We also determined that COX-2 and the EP2 receptor are present in presynaptic terminals because they are colocalized with
synaptophysin, a presynaptic marker. These results collectively indicate that
celecoxib inhibits
glutamate release from nerve terminals by reducing voltage-dependent Ca(2+) entry through a signaling cascade involving EP2 and PKA.