Modulation Of Chronic Hypoxia-Induced Chemoreceptor Hypersensitivity By Nadph Oxidase Subunits In Rat Carotid Body

He L, Liu X, Chen J, Dinger B, Stensaas L, Fidone S. Modulation of chronic hypoxia-induced chemoreceptor hypersensitivity by NADPH oxidase subunits in rat carotid body. J Appl Physiol 108: 1304-1310, 2010. First published February 25, 2010; doi: 10.1152/japplphysiol.00766.2009.-Previous studies in our laboratory established that reactive oxygen species (ROS) generated by NADPH oxidase (NOX) facilitate the open state of a subset of K+ channels in oxygen-sensitive type I cells of the carotid body. Thus pharmacological inhibition of NOX or deletion of a NOX gene resulted in enhanced chemoreceptor sensitivity to hypoxia. The present study tests the hypothesis that chronic hypoxia (CH)-induced hypersensitivity of chemoreceptors is modulated by increased NOX activity and elevated levels of ROS. Measurements of dihydroethidium fluorescence in carotid body tissue slices showed that increased ROS production following CH (14 days, 380 Torr) was blocked by the specific NOX inhibitor 4-(2-aminoethyl) benzenesulfonyl fluoride (AEBSF, 3 mu M). Consistent with these findings, in normal carotid body AEBSF elicited a small increase in the chemoreceptor nerve discharge evoked by an acute hypoxic challenge, whereas after 9 days of CH the effect of the NOX inhibitor was some threefold larger (P < 0.001). Evaluation of gene expression after 7 days of CH showed increases in the isoforms NOX2 (similar to 1.5-fold) and NOX4 (similar to 3.8-fold) and also increased presence of the regulatory subunit p47(phox) (similar to 4.2-fold). Involvement of p47(phox) was further implicated in studies of isolated type I cells that demonstrated an similar to 8-fold and an similar to 11-fold increase in mRNA after 1 and 3 days, respectively, of hypoxia in vivo. These findings were confirmed in immunocytochemical studies of carotid body tissue that showed a robust increase of p47(phox) in type I cells after 14 days of CH. Our findings suggest that increased ROS production by NOX enzymes in type I cells dampens CH-induced hypersensitivity in carotid body chemoreceptors.