Effect of DPI on superoxide production and membrane depolarization in human neutrophils. Neutrophils were pretreated with the indicated concentration of DPI for 3 minutes and subsequently stimulated with 100 nM PMA (A-C) or 1 μM fMLP (D-F). (A,D) Superoxide production was measured by cytochrome c reduction. (B,E) Membrane potential of nonstimulated cells is indicated by “ns.” (C,F) Data are expressed as percentage of the value obtained in the DPI-free samples. In panel C, the mean ± SEM of 11 (superoxide production) and 5 (membrane depolarization) independent experiments are summarized, whereas panel F represents the data of 3 independent experiments.