Prostaglandin F 2α synthesis in the hippocampal mossy fiber synaptosomal preparation: I. Dependence in arachidonic acid, phospholipase A 2, calcium availability and membrane depolarization

Abstract

Isolated hippocampal mossy fiber synaptosomes were used to characterize control mechanisms of prostaglandin F 2α (PGF 2α) synthesis at a central mammalian synapse. Exogenous arachidonic acid stimulated the dose-dependent synthesis of PGF 2α, as did the addition of phospholipase A 2 or the activation of endogenous phospholipase A 2. Phospholipase A 2 inhibitors attenuated prostaglandin synthesis, but phospholipase C inhibitors had no effect. However, a diglyceride kinase inhibitor reduced PGF 2α accumulation. The cyclooxygenase inhibitor ibuprofen eliminated PGF 2α production, while the lipoxygenase inhibitors baicalein and NDGA reduced PGF 2α accumulation. The CA 2+-ionophore-dependent stimulation of PGF 2α synthesis was abolished by Cd 2+ or Ni 2+. Further more, PGF 2α production appeared to be dependent on Ca 2+ influx via L-type, but not N- or T-type, voltage-sensitive Ca 2+ channels. Membrane depolarization with KC1, veratridine or 4-aminopyridine stimulated the synthesis of PGF 2α. This depolarization-dependent stimulation of PGF 2α synthesis was attenuated by L-type voltage-sensitive Ca 2+ channel blockers, phospholipase A 2 inhibitors, a K + channel activator and a Na + channel blocker. The activation of protein kinase C also led to a reduction of PGF 2α accumulation in depolarized nerve endings. These results may be used to suggest that PGF 2α production by hippocampal mossy fiber synaptosomes was controlled by the Ca 2+- and phospholipase A 2-dependent accumulation of unesterified arachidonic acid and was modulated by membrane depolarization and the activity of protein kinase C.