Dynamic Ca2+ changes in neutrophil phagosomes - A source for intracellularCa2+ during phagolysosome formation?

An increase in cytosolic Ca2+ concentration periphagosomally is critical fo r phagolysosomal formation and neutrophil elimination of microbes. The Ca2 increase could be achieved through release of Ca2+ from mobilized intracel lular stores. Alternatively, Ca2+ that passively enter the phagosome during phagocytosis could be provided by the phagosome. Intraphagosomal Ca2+ chan ges in single human neutrophils was measured during phagocytosis of serum o psonized Fura-2-conjugated zymosan particles, using a digital image process ing system for microspectrofluorometry. A decrease in phagosomal Ca2+ down to nanomolar concentrations was seen within minutes following phagosomal cl osure. Blockage of plasma membrane Ca2+ channels by econazole abolished thi s decrease. The fluorescence properties of Fura-2 zymosan were retained aft er phagocytosis and stable to pH changes, reactive oxygen species, and prot eolytic enzymes. We suggest that Ca2+ ions present in the phagosome enter t he cell cytosol through Ca2+ channels in the phagosomal membrane, achieving a localized Ca2+ rise that is important for phagosome processing. (C) 2000 Harcourt Publishers Ltd.