Fig. 4. Correlation of oxidative activation with Ca²⁺ and phagocytosis. (a) A typical experiment is shown in which the phagocytic event is shown by phase contrast microscopy (top row); the accompanying cytosolic free Ca²⁺ changes (middle row) and oxidative activity assessed by the DCDHF fluorescent intensity of the internalised zymosan particle (bottom row) are shown. The graph at the bottom shows the complete time course for cytosolic free Ca²⁺ change (black) and DCDHF intensity (SI) with the point of phagosomal closure marked by the arrow. In this example, a cell exhibiting a very marked 'twin peak' Ca²⁺ signal is shown. The full data is also shown in Movie 1 (available at jcs.biologists.org/supplemental) in which the oxidative signal from the particle and the Ca²⁺ signal from the neutrophil are superimposed. (b) For comparison, a cell exhibiting a 'shouldered' Ca²⁺ signal is also shown. The rows of images are as described above. In both examples, the onset of oxidative activity correlates with the second phase of the Ca²⁺ signal.