ACTIVATION OF THE OXYGEN-RADICAL-GENERATING SYSTEM IN GRANULES OF INTACT HUMAN NEUTROPHILS BY A CALCIUM IONOPHORE (IONOMYCIN)

Subcellular fractionation studies were performed on human neutrophils stimulated with ionomycin (a Ca2+-specific ionophore). The results of these studies revealed NADPH-oxidase activity, without any additive, both in the plasma membrane and in the specific granule fractions. After comparing these results with the NADPH oxidase activity induced by the ionophore in intact neutrophils, in differentiated HL-60 cells and in neutrophil cytoplasts, we conclude that ionomycin preferentially activates the NADPH oxidase pool located in the membrane of specific granules. Furthermore, we suggest that incorporation of granule membrane into the plasma membrane makes the associated NADPH oxidase less sensitive to activation induced by a rise in [Ca2+]i.