Extracellular Ca2+ regulates the respiratory burst of human neutrophils

Abstract The role of extracellular calcium in the activation of respiratory burst in human neutrophils was studied by using the receptor agonist, N -formyl-methionyl-leucyl-phenylalanine (fMLP), and the activator of protein kinase C phorbol myristate acetate (PMA). The level of intracellular free calcium was measured by using both cell suspensions and single cells in the presence and absence of extracellular calcium. The Ca 2+ -ATPase inhibitor, thapsigargin, was used to activate higher Ca 2+ influx, while a novel calcium channel blocker, panax notoginseng saponins (PNGS) was used to block the Ca 2+ entry from extracellular space during the responding period of cells. It was found that about two-thirds of the activation of respiratory burst initiated by the receptor agonist were attributed to the Ca 2+ influx under normal physiological conditions. The higher Ca 2+ influx resulted in tremendous enhancement of the intensity of respiratory burst initiated by fMLP and marked acceleration of the onset of the respiratory burst stimulated by PMA. It is evident that both intra- and extracellular Ca 2+ are required for full activation of the respiratory burst of human neutrophils, and the Ca 2+ influx from extracellular space plays an important role either in generation of reactive oxygen metabolites or in activation of protein kinase C.