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Title

Cytosolic free calcium elevation mediates the phagosome-lysosome fusion during phagocytosis in human neutrophils

Authors
Jaconi, Marisa
Magnusson, K. E.
Sjogren, M.
Stendahl, O.
Published in The Journal of Cell Biology. 1990, vol. 110, no. 5, p. 1555-1564
Abstract Cytosolic free calcium ([Ca2+]i) and fusion of secondary granules with the phagosomal membrane (phagosome-lysosome fusion, P-L fusion) were assessed in single adherent human neutrophils during phagocytosis of C3bi-opsonized yeast particles. Neutrophils were loaded with the fluorescent dye fura2/AM and [Ca2+]i was assessed by dual excitation microfluorimetry. Discharge of lactoferrin, a secondary granule marker into the phagosome was verified by immunostaining using standard epifluorescence, confocal laser scanning and electron microscopy. In Ca2(+)-containing medium, upon contact with a yeast particle, a rapid rise in [Ca2+]i was observed, followed by one or more Ca2+ peaks (maximal value 1,586 nM and median duration 145 s): P-L fusion was detected in 80% of the cells after 5-10 min. In Ca2(+)-free medium the amplitude, frequency and duration of the [Ca2+]i transients were decreased (maximal value 368 nM, mostly one single Ca2+ peak and median duration 75 s): P-L fusion was decreased to 52%. Increasing the cytosolic Ca2+ buffering capacity by loading the cells with MAPT/AM led to a dose-dependent inhibition both of [Ca2+]i elevations and P-L fusion. Under conditions where basal [Ca2+]i was reduced to less than 20 nM and intracellular Ca2+ stores were depleted, P-L fusion was drastically inhibited while the cells ingested yeast particles normally. P-L fusion could be restored in Ca2(+)-buffered cells containing ingested particles by elevating [Ca2+]i with the Ca2(+)-ionophore ionomycin. The present findings directly indicate that although the ingestion step of phagocytosis is a Ca2(+)-independent event, [Ca2+]i transients triggered upon contact with opsonized particles are necessary to control the subsequent fusion of secondary granules with the phagosomal membrane.
Keywords Benzofurans/diagnostic useCalcium/metabolism/ physiologyCytosol/metabolismEgtazic Acid/diagnostic useFluorescent Antibody TechniqueFluorescent Dyes/diagnostic useFura-2/ analogs & derivativesHumansImmunohistochemistryLactoferrin/metabolismLysosomes/metabolism/ physiologyMembrane Fusion/physiologyMicroscopy, ElectronNeutrophils/ metabolismPhagocytosis/ physiologyPhagosomes/metabolism/ physiology
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PMID: 2110568
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Other version: http://jcb.rupress.org/content/110/5/1555.full.pdf
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JACONI, Marisa et al. Cytosolic free calcium elevation mediates the phagosome-lysosome fusion during phagocytosis in human neutrophils. In: The Journal of Cell Biology, 1990, vol. 110, n° 5, p. 1555-1564. https://archive-ouverte.unige.ch/unige:7350

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Deposited on : 2010-06-21

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