NADPH oxidase is an O 2 sensor in airway chemoreceptors: Evidence from K + current modulation in wild-type and oxidase-deficient mice

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Abstract
Pulmonary neuroepithelial bodies (NEBs) are presumed airway chemoreceptors that express the putative O2 sensor protein NADPH oxidase and O2-sensitive K+ channels K+(O2). Although there is a consensus that redox modulation of K+(O2) may be a common O2-sensing mechanism, the identity of the O2 sensor and related coupling pathways are still controversial. To test whether NADPH oxidase is the O2 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 gp91phox subunit coding region by insertion of a neomycin phosphotransferase (neo) gene. Expression in NEB cells of neo mRNA, a marker for nonfunctional gp91phox, was confirmed by nonisotopic in situ hybridization. In WT cells, hypoxia (pO2 = 15–20 mmHg; 1 mmHg = 133 Pa) caused a reversible inhibition (≈46%) of both Ca2+-independent and Ca2+-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 (H2O2; 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, H2O2 restored K+ current amplitude in the presence of diphenylene iodonium. We conclude that NADPH oxidase acts as the O2 sensor in pulmonary airway chemoreceptors.