An inhibitor of cyclic AMP-dependent protein kinase enhances the superoxide production of human neutrophils stimulated by N-formyl-methionyl-leucyl-phenylalanine.

Intact human neutrophils produced superoxide (O2-) by the stimulation with N-formyl-methionyl-leucyl-phenylalanine (fMLP) even when the extracellular Ca2+ was absent (0.56 +/- 0.13 nmol/min per 10(6) cells). The production by fMLP was enhanced more than twice in the presence of the extracellular Ca2+. Moreover, the O2- production by fMLP in the presence of extracellular Ca2+ was enhanced nearly three times by the treatment of cells with H-89, an inhibitor of cyclic AMP-dependent protein kinase (PKA). The enhancement was not observed when the extracellular Ca2+ was depleted from the reaction mixture. In addition, H-89 did not enhance fMLP-induced O2- production of electropermeabilized neutrophils in which the intracellular Ca2+ concentration was fixed to about 100 nM. These observations suggest that not only Ca2+ influx but the inhibition of PKA is necessary for the maximum O2- production by fMLP and that the O2- production is partially suppressed by the activation of PKA induced by fMLP.