pH measurement on isolated phagosomes.

<p>Intra-vesicular pH of phagosomes containing FITC-labeled zymosan was determined in untreated control preparations (left panel), untreated preparations from Stat1−/− BMMs (middle panel), and control preparations treated with 93 mM K₂SO₄ (right panel). Acidification was initiated by addition of 2.5 mM ATP and 1 mM MgSO₄ (closed arrow). Subsequent addition of 20 µM NH₄Cl increased the pH of all phagosome preparations (open arrow). The addition of 10 µM nigericin increased the pH to 7 (not shown). Each time course was done in triplicate with the standard deviation indicated by the error bars.