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 H 2O 2, 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 Ca 2+-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 Ca 2+, a further increase by azide of the intracellular Ca 2+-level of cells stimulated with fMLP/CB provides a likely mechanism for the enhancement of fMLP/CB-induced exocytosis by azide.