Peroxynitrite may contribute to oxidative stress involving neurodegeneration in several disorders, including Alzheimer's disease. As with other reactive oxygen species, peroxynitrite might affect neuronal signalling systems, actions that could contribute to adaptive or deleterious cellular outcomes, but such effects have not previously been studied. To address this issue directly, peroxynitrite (50–500 µM) was administered to human neuroblastoma SH-SY5Y cells to assess its effects on protein tyrosine nitration, phosphoinositide signalling and protein tyrosine phosphorylation. Peroxynitrite rapidly increased the nitrotyrosine immunoreactivity of numerous proteins, primarily in the cytosol. Peroxynitrite inhibited, in a concentration-dependent manner, phosphoinositide hydrolysis stimulated by activation of muscarinic receptors with carbachol and the inhibition was greater after the depletion of cellular glutathione. In comparison, muscarinic receptor-stimulated phosphoinositide hydrolysis in human astrocytoma 1321N1 cells was less vulnerable to inhibition by peroxynitrite either without or with prior depletion of glutathione. There was a large, rapid and reversible increase in the tyrosine phosphorylation of the p120 Src substrate in peroxynitrite-treated SH-SY5Y cells, a response that was potentiated by glutathione depletion; in contrast, peroxynitrite decreased the tyrosine phosphorylation of focal adhesion kinase and paxillin. Tyrosine phosphorylation of p120 in 1321N1 astrocytoma cells was less sensitive to modulation by peroxynitrite. Thus alterations in phosphoinositide signalling and protein tyrosine phosphorylation were greater in neuroblastoma than astrocytoma cells, and modulation of these signalling processes probably contributes to neuronal mechanisms of the response to peroxynitrite.

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