ATP was measured in the sterile filtrates of HL-60 cells using the Sigma Luciferase ATP assay kit as previously described (9). We used an ATP regenerating system consisting of 100 μg/ml creatine kinase and 15 mM phosphocreatine to prevent destruction of extracellular ATP during the 2-h assay.
Polarization microscopy for birefringent crystals was performed as described previously (6).
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