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

Abstract

Pulmonary neuroepithelial bodies (NEBs) are presumed airway chemoreceptors that express the putative O2 sensor protein NADPH oxidase and O 2-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 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 oxidasedeficient (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 situ hybridization. In WT cells, hypoxia (pO2 ‫؍‬ 15-20 mmHg; 1 mmHg ‫؍‬ 133 Pa) caused a reversible inhibition (Ϸ46%) 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 M), an inhibitor of the oxidase, reduced K ؉ current by Ϸ30% 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 O 2 sensor in pulmonary airway chemoreceptors.

Activation Mechanism of Gi and Go by Reactive Oxygen Species

“…Intracellular signaling proteins such as NADPH oxidase (34), ryanodine receptor (32), and K ϩ channel (31) can work as redox sensors (33). Our results add G i and G o to the growing members of the redox-sensing protein family.…”

NADPH oxidases in lung biology and pathology: Host defense enzymes, and more

“…In the respiratory tract, pulmonary neuroepithelial bodies (NEBs) within the airway mucosa represent specialized pulmonary structures that are composed of clusters of innervated amine-and peptide-containing cells, and are involved in mediating airway responses to hypoxia. Based on studies with NADPH oxidase inhibitors and gp91phox (NOX2)-deficient mice, it has been demonstrated that these responses are due to the presence of NOX2, which acts as an oxygen sensor by regulating O 2 -sensitive K+ currents, via altered production of ROS (4,175). NADPH oxidase (most likely NOX2) has been suggested to play a more universal role as oxygen sensor in various tissues, thereby mediating hypoxic pulmonary vasoconstriction, vascular smooth muscle function, and carotid and airway chemoreceptor activation (4).…”

Pro-metastatic signaling by c-Met through RAC-1 and reactive oxygen species (ROS)

“…It is interesting to note that the Rac-ROS signaling module has also been implicated in oxygen sensing (Fu et al, 2000), and may therefore have a specific role in directing circulating malignant cells towards the lungs along a chemotactic gradient of pO 2 .…”