Pulmonary neuroepithelial bodies (NEBs) are presumed airway chemoreceptors that express the putative O 2 sensor protein NADPH oxidase and O 2 -sensitive K + channels K + (O 2 ). Although there is a consensus that redox modulation of K + (O 2 ) may be a common O 2 -sensing mechanism, the identity of the O 2 sensor and related coupling pathways are still controversial. To test whether NADPH oxidase is the O 2 sensor in NEB cells, we performed patch-clamp experiments on intact NEBs identified by neutral red staining in fresh lung slices from wild-type (WT) and oxidase-deficient (OD) mice. In OD mice, cytochrome
b558 and oxidase function was disrupted in the gp91 phox subunit coding region by insertion of a neomycin phosphotransferase (neo) gene. Expression in NEB cells of neo mRNA, a marker for nonfunctional gp91 phox , was confirmed by nonisotopic in situhybridization. In WT cells, hypoxia (pO 2 = 15–20 mmHg; 1 mmHg = 133 Pa) caused a reversible inhibition (≈46%) of both Ca 2+ -independent and Ca 2+ -dependent K + currents. In contrast, hypoxia had no effect on K + current in OD cells, even though both K + current components were expressed. Diphenylene iodonium (1 μM), an inhibitor of the oxidase, reduced K + current by ≈30% in WT cells but had no effect in OD cells. Hydrogen peroxide (H 2 O 2 ; 0.25 mM), a reactive oxygen species generated by functional NADPH oxidase, augmented K + current by >30% in both WT and OD cells; further, in WT cells, H 2 O 2 restored K + current amplitude in the presence of diphenylene iodonium. We conclude that NADPH oxidase acts as the O 2 sensor in pulmonary airway chemoreceptors.