Hydrogen Peroxide Enhances Signal-Responsive Arachidonic Acid Release from Neurons: Role of Mitogen-Activated Protein Kinase

Abstract: Hydrogen peroxide (H₂O₂) is a potent stimulator of signal-responsive phospholipase A₂ (PLA₂) in vascular smooth muscle and cultured endothelial cells. We investigated whether H₂O₂ plays a similar regulatory role in neurons. H₂O₂ did not stimulate a release of arachidonic acid from cultured neurons when applied alone but strongly enhanced the liberation of arachidonic acid evoked by maximally effective concentrations of either glutamate, the glutamate receptor agonist N-methyl-d -aspartate (NMDA), the muscarinic receptor agonist carbachol, the Na⁺-channel opener veratridine, or the Ca²⁺-ionophore ionomycin. The potentiating effects of H₂O₂ were strongly inhibited in the presence of the PLA₂ inhibitor mepacrine, suggesting that the site of action was within the signal responsive arachidonic acid cascade. The enhancing effect of H₂O₂ was not reversed by protein kinase C inhibitors (chelerythrine chloride or GF 109203X) nor was it mimicked by phorbol ester treatment. H₂O₂ alone strongly enhanced the levels of immunodetectable activated mitogen-activated protein kinase (activated MAP kinases ERK1 and ERK2) in a Ca²⁺-dependent manner and this effect was additive with increases in the levels of activated MAP kinase evoked by glutamate. The enhanced release of arachidonic acid, however, was not clearly reversed by the MAP kinase kinase (MEK) inhibitor PD 98059, although this treatment effectively abolished H₂O₂ activation of MAP kinase. Thus, MAP kinase activation and Ca²⁺-dependent arachidonic acid release are regulated by oxidative stress in cultured striatal neurons.