Phospholipase C and phosphatidylinositol 3‐kinase signaling are involved in the exogenous arachidonic acid‐stimulated respiratory burst in human neutrophils

To define the role of phospholipase C (PLC) and phosphatidylinositol 3-kinase (PI-3K), signaling pathways in arachidonic acid (AA)-stimu- lated respiratory burst in human neutrophils, the AA-stimulated respiratory burst, Ins(1,4,5)P 3 pro- duction, PI-3K activation, and cytoplasmic Ca 2 mobilization were investigated. It was found that Ins(1,4,5)P 3 production and PI-3K activity in AA- stimulated cells were increased in a dose-depen- dent manner. U73122, the PLC inhibitor, effec- tively inhibited the AA-stimulated respiratory burst and Ca 2 release from the intracellular calcium store but not the activity of PI-3K, indicating the independence of PI-3K signaling on PLC activa- tion. Wortmannin, the PI-3K inhibitor, at the con- centration sufficient to inhibit PI-3K activity, can only partially inhibit Ca 2 release from the internal store, indicating a partial regulation of PLC signal- ing by PI-3K and the existence of two pathways initiated by different PLC subfamilies. One is reg- ulated by PI-3K activation, and the other is inde- pendent of PI-3K signaling. It was observed that AA could still induce a noncapacitative Ca 2 entry in the cells when Ca 2 release from the intracellu- lar store was blocked by a PLC inhibitor, or a capacitative Ca 2 entry was induced by preincuba- tion with thapsigargin. However, the AA-mediated, noncapacitative Ca 2 entry seems to play a little, if any, role in the stimulated respiratory burst. The present study suggests that the PLC signaling path- way, which may be activated by PLC and PLC, respectively, and the PI-3K signaling pathway are involved in the AA-stimulated respiratory burst in human neutrophil. J. Leukoc. Biol. 74: 000-000; 2003.