Peroxynitrite regulates exocytosis of neutrophil granules

Peroxynitrite is formed in the organism by activated neutrophils as a result of the enhanced production of nitrogen monoxide and superoxide anion radical in the inflammation foci. Since peroxynitrite modifies the structure of macromolecules, including the elements of actin cytoskeleton, it can influence signal transduction pathways that regulate intracellular granule exocytosis. In this paper we explore a dual effect of peroxynitrite on the processes of neutrophil degranulation by the methods of flow cytometry, light microscopy, and atomic force microscopy. We showed that peroxynitrite at concentrations less than 300 μM activated graded exocytosis of neutrophil intracellular granules, which resulted in the enhancement of neutrophil adhesion to the substrate, cell spreading on the substrate, and activation of neutrophil ability to kill microorganisms. Peroxynitrite at higher concentrations inhibited exocytosis of neutrophil granules and hindered cell adhesion to the substrate. The character of influence of the specific agents, such as colchicine and cytochalasin that selectively disrupt cytoskeletal structures, on peroxynitrite-induced changes in neutrophil morphology indicates an important role of actin cytoskeleton in the regulation of intracellular granule exocytosis induced by peroxynitrite. Our results support the hypothesis suggesting that peroxynitrite is a natural regulator of neutrophil effector functions.