Cytosolic pH changes in VSOP/Hv1^−/− neutrophils. Bone marrow neutrophils were loaded with the pH-sensitive dye BCECF and changes in fluorescence ratio (F490/F440) measured in sodium-free solutions to minimize the contribution of Na⁺/H⁺ exchange. (A) Representative ratio images of WT and VSOP/Hv1^−/− neutrophils before (left) and after (right) addition of PMA. Bar, 10 µm. (B) Cytosolic pH distribution of all the PMA-treated cells. (C) Mean cytosolic pH of resting and PMA-activated neutrophils. Data are means ± SD of three experiments with >100 cells each from two WT and two VSOP/Hv1^−/− mice. **, P < 0.01; *, P < 0.05, unpaired Student's t test.