Role of enhanced inositol phospholipid metabolism in neutrophil activation

When guinea pig neutrophils were stimulated with chemotactic peptide [formylmethionyl-leucyl-phenylalanine (fMLP)], a marked release of lysosomal enzyme and production of superoxide anion were detected. The breakdown of phosphatidylinositol 4,5-bisphosphate (TPI) and the subsequent formation of diacylglycerol, phosphatidic acid and free arachidonic acid also occurred during the processes. Ca2+ ionophore A23187 caused an evident secretion of lysosomal enzyme but no superoxide anion production. Ca2+ ionophore also caused TPI breakdown to diacylglycerol although this breakdown was not as significant as that detected by fMLP. The tumor promotor tetradecanoylphorbol acetate (TPA), which is a strong activator of superoxide anion production but not a good stimulator of lysosomal enzyme secretion, did not cause a significant decrease of TPI or arachidonic acid release. Since TPA is known not to increase the intracellular Ca2+ level, these results suggest that lysosomal enzyme secretion is correlated closely with enhanced inositol phospholipid metabolism and Ca2+-dependent processes. On the other hand, superoxide anion production seemed to be caused mainly by Ca2+-independent processes, perhaps by protein kinase-C activation through newly formed diacylglycerol, when neutrophils were activated by chemotactic peptide.