Activation of human neutrophils by substance P. Effect on oxidative metabolism, exocytosis, cytosolic Ca2+ concentration and inositol phosphate formation.

The neuropeptide substance P (SP), which has been suggested to mediate neurogenic inflammation, induces in human neutrophils the activation of the respiratory burst measured as O2 consumption and H2O2 production, and a cytochalasin B-dependent secretion of specific and azurophilic granules. The SP(4-11) fragment is much more stimulant than the entire molecule, whereas the SP(1-4) fragment is inactive. The respiratory and secretory response to SP are associated with an activation of phosphoinositide turnover, of Ca2+ influx and release from intracellular stores. Pertussis toxin inhibits 70% of the respiratory response and the residual 30% activity remains, even increasing 10-fold the concentration of the toxin. 1-(5-Isoquinolinesulfonyl)-2-methylpiperazine, a putative inhibitor of protein kinase C, does not modify the respiratory response to SP. Cytochalasin B significantly depresses the activation of the respiration by SP, whereas it moderately enhances the activation of phosphoinositide turnover and potentiates the increase of intracellular Ca2+ concentration. The results are discussed in relation to the receptor apparatus involved in SP activity, the signal transduction sequence activated by SP for the stimulation of NADPH oxidase, and the role of cell response to SP in the inflammatory process.