In rat cerebrocortical synaptosomes, the addition of 4β-phorbol dibutyrate (4β-PDBu) and arachidonic acid enhances and decreases, respectively, the glutamate release evoked by 4-aminopyridine. Pretreatment of synaptosomes with 12-O-tetradecanoylphorbol 13-acetate (TPA) or preincubation with staurosporine, prevent the stimulatory effect of 4β-PDBu, but are without effect on the inibitory action of arachidonic acid. Moreover, methyl arachidonate, which is not effective as a PKC activator, also strongly inhibits glutamate exocytosis. These results suggest that PKC is not involved in the inhibition of glutamate release by arachidonic acid.
