Abstract
Human neutrophils maximally stimulated with the optimal concentration (100 ng/ml) of phorbol myri-state acetate (PMA), a direct activator of protein kinase C (PKC), for 5 min at 37°C did not respond with superoxide (O-2) release to the later addition of PMA itself or the Ca2+ionophore ionomycin. The loss of responsiveness to the later addition of ionomycin was dependent on the interval between the addition of PMA and ionomycin. However, these cells did respond with enhanced release of O-2to the later addition of N-formyl-methionyl-leucyl-phenylalanine (FMLP) or concanavalin A (Con A) ·In these PMA-pretreated cells, an increase in cytoplasmic free Ca2+ ( [Ca2+] i) induced by ionomycin was unaffected, whereas that induced by FMLP was inhibited by 50-60% and that induced by Con A was completely abolished. UCN-01, a PKC inhibitor, inhibited O-2release induced by PMA, but not by FMLP.
These findings suggest that FMLP and Con A trigger the respiratory burst in human neutrophils by activating the definite pathway which include other signals than activation of PKC and an increase in [Ca2+] i.
