Intracellular free calcium regulates the onset of the respiratory burst ofhuman neutrophils activated by phorbol myristate acetate

Thapsigargin was used to study the regulation of different static calcium l evel ([Ca2+](i)) on the respiratory burst of human neutrophils stimulated w ith phorbol myristate acetate (PMA). The result showed that the onset time of the respiratory burst was obviously reduced by elevation of static [Ca2](i) but is still much longer than that stimulated with N-formylmethionylle ucylphenylalanine (fMLP). To find the reason, the onset times of the respir atory burst stimulated with fMLP, 1,2-dioctanoyl-sn-glycerol (DiC8), and PM A were determined at different static [Ca2+](i). It turns out that although DiC8 was unable to induce the respiratory burst at low [Ca2+](i), the onse t time of DiC8-stimulated response at high [Ca2+](i) was almost the same as that stimulated with fMLP. The study revealed that the fast onset of the f MLP-stimulated respiratory burst in comparison with PMA-stimulated response is not only due to the transient rise of [Ca2+](i), but is also due to the higher efficiency of diacylglycerol (DAG) in activating protein kinase c ( PKC). The determining step in governing the onset of a respiratory burst is the activation of PKC. CELL SIGNAL 11;5:355-360, 1999. (C) 1999 Elsevier S cience Inc.