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

Abstract Thapsigargin was used to study the regulation of different static calcium level ([Ca 2+ ] i ) on the respiratory burst of human neutrophils stimulated with phorbol myristate acetate (PMA). The result showed that the onset time of the respiratory burst was obviously reduced by elevation of static [Ca 2+ ] i but is still much longer than that stimulated with N-formylmethionylleucylphenylalanine (fMLP). To find the reason, the onset times of the respiratory burst stimulated with fMLP, 1,2-dioctanoyl-sn-glycerol (DiC8), and PMA were determined at different static [Ca 2+ ] i . It turns out that although DiC8 was unable to induce the respiratory burst at low [Ca 2+ ] i , the onset time of DiC8-stimulated response at high [Ca 2+ ] i was almost the same as that stimulated with fMLP. The study revealed that the fast onset of the fMLP-stimulated respiratory burst in comparison with PMA-stimulated response is not only due to the transient rise of [Ca 2+ ] 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.