Sodium azide enhances neutrophil migration and exocytosis: Involvement of nitric oxide, cyclic GMP and calcium

Azide, in the absence of other stimuli, enhanced neutrophil migration in a chemotactic way. The effect of azide on migration was significant at concentrations ≥ 1 μM and maximal at 10 μM azide. Although azide itself could not induce exocytosis, at concentrations ≥ 10 μM azide enhanced exocytosis induced by a combination of the chemotactic peptide f-methionyl-leucyl-phenylalanine (fMLP) and cytochalasin B (CB). Azide can be oxidized by catalase and myeloperoxidase in the presence of H2O2, resulting in the generation of nitric oxide (NO). Formation of NO from azide was detected by ESR spectroscopy with carboxy-PTIO as a NO-selective probe, and by measurement of nitrite formation. Azide-induced migration, and the enhancement by azide of fMLP/CB-induced exocytosis, were blocked by pre-incubating cells with aminotriazole, an inhibitor of catalase and myeloperoxidase, suggesting that the effect of azide was mediated by NO. Azide-induced migration, but not the enhancement by azide of fMLP/CB-induced exocytosis, was inhibited to a large extent by inhibitors of soluble guanylate cyclase and by inhibitors of cGMP-dependent protein kinase. These observations suggest that azide-induced migration is mediated via cGMP and cGMP-dependent protein kinase, while the enhancement of fMLP/CB-induced exocytosis is not. Azide caused a sustained elevation of the intracellular Ca2+-concentration of neutrophils stimulated with fMLP/CB, which was not affected by inhibitors of the cGMP-signalling cascade. Since neutrophil exocytosis has been shown to be closely correlated with increases in intracellular Ca2+, a further increase by azide of the intracellular Ca2+-level of cells stimulated with fMLP/CB provides a likely mechanism for the enhancement of fMLP/CB-induced exocytosis by azide.