Abstract
Human neutrophils exposed to chemotactic concentrations of zymosan- activated serum (ZAS) and a formylated chemotactic peptide (FMLP, 10(- 7)--10(-9) M) were markedly enhanced in their ability to generate superoxide (O2-) upon stimulation with either sodium fluoride or phorbol myristate acetate (PMA). For both fluoride and PMA, enhancement was characterized by a decrease in the lag from stimulation to initiation of superoxide release and by an increase in the rate of superoxide generation--representing faster activation and increased activity of O2- generating enzyme, respectively. Chemotactic concentrations of casein, normal serum, and casein-treated serum enhanced the activity, but not the rate of activation, of the fluoride- stimulated superoxide generating system. This effect on activity was not so impressive as that obtained with FMLP or ZAS. The mechanisms by which FMLP enhanced responsiveness to fluoride and PMA were found to be different. Optimal enhancement for fluoride-stimulated responses required extracellular Ca++. Extracellular glucose, but not extracellular Ca++, was required for enhancement of FMLP of PMA- stimulated responses. A similar glucose requirement could not be demonstrated for chemotactic peptide enhancement of the superoxide- generating system stimulated by fluoride. Fluoride and PMA apparently activate the neutrophil O2- generating enzyme by pathways that are not identical. However, responsiveness of the enzyme to both agents is susceptible to modulation by cellular responses to chemotactic peptides.
