The role of Ca²⁺ and Ca²⁺-activated phospholipid-dependent protein kinase in degranulation of human neutrophils

The degranulation reactions of human neutrophils induced by 1-oleoyi-2-acetyiglycerol (OAG), phorbol 12-myristate 13-acetate (PMA), and calcium ionophore A23187 or their combinations, were studied. OAG in the absence of the Ca²⁺-ionophore A23187 stimulated the releases of both lysozyme and lactoferrin, constituents of the specific granules, but did not stimulate the release of β-glucuronidase, an enzyme of the azurophil granules. Electron microscopy revealed a selective decrease in the numbers of the specific granules in this case. The combined effects of A23187 at a concentration higher than 0.1 μM and OAG were essentially additive. W-7, known to be an inhibitor of both Ca²⁺-activated phospholipid-dependent protein kinase (C-kinase) and calmodulin, inhibited the degranulation induced by OAG or PMA, while it inhibited the reaction induced by A23187 less markedly. The release of lysozyme reached a plateau at about 0.1 μM A23187 and increased again at higher concentrations of A23187. The observations suggest that degranulation can be induced by the activation of the C-kinase, and the degranulation by A23187 at low concentrations may be due to the activation of the C-kinase; the effects of A23187 at high concentrations, however, could not be explained only in terms of the activation of the C-kinase.