Effects of mitochondrial poisons on glutathione redox potential and carotid body chemoreceptor activity

Low oxygen sensing in chemoreceptor cells involves the inhibition of specific plasma membrane K+ channels, suggesting that mitochondria-derived reactive oxygen species (ROS) link hypoxia to K+ channel inhibition, subsequent cell depolarization and activation of neurotransmitter release. We have used several mitochondrial poisons, alone and in combination with the antioxidant N-acetylcysteine (NAC), and quantify their capacity to alter GSH/GSSG levels and glutathione redox potential (EGSH) in rat diaphragm. Selected concentrations of mitochondrial poisons with or without NAC were tested for their capacity to activate neurotransmitter release in chemoreceptor cells and to alter ATP levels in intact rat carotid body (CB). We found that rotenone (1 μM), antimycin A (0.2 μg/ml) and sodium azide (5 mM) decreased EGSH; NAC restored EGSH to control values. At those concentrations mitochondrial poisons activated neurotransmitter release from CB chemoreceptor cells and decreased CB ATP levels, NAC being ineffective to modify these responses. Additional experiments with 3-nitroprionate (5 mM), lower concentrations of rotenone and dinitrophenol revealed variable relationships between EGSH and chemoreceptor cell neurotransmitter release responses and ATP levels. These findings indicate a lack of correlation between mitochondrial-generated modifications of EGSH and chemoreceptor cells activity. This lack of correlation renders unlikely that alteration of mitochondrial production of ROS is the physiological pathway chemoreceptor cells use to signal hypoxia.