Nitric oxide induces tyrosine nitration and release of cytochrome c preceding an increase of mitochondrial transmembrane potential in macrophages

Treatment of elicited peritoneal macrophages or the macrophage cell line RAW 264.7 with high concentrations of nitric oxide donors is followed by apoptotic cell death. Analysis of the changes in the mitochondrial transmembrane potential (Delta Psi(m)) with specific fluorescent probes showed a rapid and persistent increase of Delta Psi(m), potential that usually decreases in cells undergoing apoptosis through mitochondrial-dependent mechanisms. Using confocal microscopy, the release of cytochrome c from the mitochondria to the cytosol was characterized as an early event preceding the rise of Delta Psi(m). The cytochrome c from cells treated with nitric oxide donors was modified chemically, probably through the formation of nitrotyrosine residues, suggesting the synthesis of peroxynitrite in the mitochondria, These results indicate that nitric oxide-dependent apoptosis in macrophages occurs in the presence of a sustained increase of Delta Psi(m), and that the chemical modification and release of cytochrome c from the mitochondria precede the changes of Delta Psi(m).