The role of protein kinase C and [Ca2+]i in superoxide anion synthesis and myeloperoxidase degranulation of human neutrophils.

A chemiluminescence procedure has been developed to determine superoxide anion (O2-) generation and myeloperoxidase (MPO) release from human activated neutrophils. By using this procedure, the role of protein kinase C (PKC) and cytosolic calcium ion (Ca2+[i) for O2- generation and MPO release was examined. Activation of Fc gamma R on neutrophils with IgG-coated zymosan (IgGZ) caused a transient rise of Ca2+[i, followed by O2- generation and MPO release. A PKC inhibitor suppressed completely the O2- generation and slightly the MPO release. Direct activation of PKC by a specific PKC activator, phorbol myristate acetate (PMA), induced a remarkable O2- generation and a small MPO release, indicating that PKC may regulate entirely O2- synthesis and partially MPO degranulation. Influx of extracellular Ca2+ induced by the calcium ionophore A23187 provoked MPO release only. Complete inhibition of this MPO release with a Ca2+/calmodulin (CaM)-coupling inhibitor and a CaM inhibitor provides evidence that Ca2+[i may regulate MPO degranulation through direct activation of CaM, but not PKC. The Ca2+/CaM inhibitors significantly prevented IgGZ-induced O2- generation and MPO release, while they did not affect PMA-induced O2- generation and MPO release. These results suggest that in Fc gamma R-stimulated neutrophils, Ca2+[i activates CaM, which in turn mediates not only activation of PKC-induced O2- synthesis and MPO degranulation, but also MPO degranulation without PKC intermediate.