Superoxide in bone marrow PMNs from BK^+/+ and BK^−/− mice. Net superoxide production as well as the kinetics over 60 minutes by PMA-stimulated PMNs was the same in normal and BK^−/− mice (A). The BK channel inhibitor IbTX had no effect on extracellular superoxide generation by either PMN population (B). Superoxide generation after opsonized zymosan was the same in BK^+/+ and BK^−/− cells (C). Intracellular NADPH oxidase activity, assessed as the DHR oxidation by stimulated PMNs measured and quantitated as mean fluorescent intensity (MFI), was the same in BK^+/+ and BK^−/− cells (D) based on the light scatter characteristics (E). PMNs specific GR-1 staining in whole blood indicated that the gated populations used to assess DHR oxidation were indeed PMNs (F).