Pardaxin (PX) is a voltage-dependent ionophore that stimulates catecholamine exocytosis from PC-12 pheochromocytoma cells both in the presence and absence of extracellular calcium. Using a battery of phospholipase A2 inhibitors we show that PX stimulation of phospholipase A2 (PLA2) enzymes is coupled with induction of exocytosis. We investigated the relationship between PX-induced PLA2 activity and neurotransmitter release by measuring the levels of arachidonic acid (AA), prostaglandin E2 (PGE2), and dopamine release. In the presence of extracellular calcium, the cytosolic PLA2 inhibitor arachidonyl trifluoromethyl ketone (AACOCF3) inhibited by 100, 70, and 73%, respectively, the release of AA, PGE2, and dopamine induced by PX. The mitogen-activated protein kinase/extracellular signal-regulated kinase inhibitor 2′-amino-3′-methoxyflavone (PD98059) reduced by 100 and 82%, respectively, the release of AA and PGE2 induced by PX. In the absence of extracellular calcium, the calcium-independent PLA2 (iPLA2) inhibitors methyl arachidonyl fluorophosphonate, AACOCF3, and bromoenol lactone (BEL) inhibited by 80 to 90% PX stimulation of AA release, by 65 to 85% PX stimulation of PGE2 release, and by 80 to 90% PX-induced dopamine release. Using vesicle fusion-based enzyme-linked immunosorbent assay we found similar levels of inhibition of PX-induced exocytosis by these inhibitors. Also, PX induced the formation of soluble N-ethylmaleimide-sensitive factor attachment protein receptor complexes, an effect that was augmented by N-methylmaleimide. This complex formation was completely inhibited by BEL. Botulinum toxins type C1 and F significantly inhibited the release of AA, PGE2, and dopamine induced by PX. Our data suggest that PX stimulates exocytosis by activating cystolic PLA2 and iPLA2, leading to the generation of AA and eicosanoids, which, in turn, stimulate vesicle competence for fusion and neurotransmitter release.
|Original language||American English|
|Number of pages||10|
|Journal||Journal of Pharmacology and Experimental Therapeutics|
|State||Published - 2002|