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 (O-2(-)) by the stimulati on with N-formyl-methionyl-leucyl-phenylalanine (fMLP) even when the e xtracellular 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 o f the extracellular Ca2+. Moreover, the O-2(-) production by fMLP in t he presence of extracellular Ca2+ was enhanced nearly three times by t he treatment of cells with H-89, an inhibitor of cyclic AMP-dependent protein kinase (PKA). The enhancement was not observed when the extrac ellular Ca2+ was depleted from the reaction mixture. In addition, H-89 did not enhance fMLP-induced O-2(-) production of electropermeabilize d 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 O-2(-) producti on by fMLP and that the O-2(-) production is partially suppressed by t he activation of PKA induced by fMLP.