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Reduced to oxidized glutathione ratios and oxygen sensing in calf and rabbit carotid body chemoreceptor cells

G. Sanz-Alfayate, A. Obeso, M. T. Agapito and C. González

1. The aim of this work was to test the redox hypotheses of O₂ chemoreception in the carotid body (CB). They postulate that hypoxia alters the levels of reactive oxygen species (ROS) and the ratio of reduced to oxidized glutathione (GSH/GSSG), causing modifications to the sulfhydryl groups/disulfide bonds of K⁺ channel proteins, which leads to the activation of chemoreceptor cells.
2. We found that the GSH/GSSG ratio in normoxic calf CB (30.14 ± 4.67; n = 12) and hypoxic organs (33.03 ± 6.88; n = 10), and the absolute levels of total glutathione (0.71 ± 0.07 nmol (mg tissue)^-1, normoxia vs. 0.76 ± 0.07 nmol (mg tissue)^-1, hypoxia) were not statistically different.
3. N-Acetylcysteine (2 mM; NAC), a precursor of glutathione and ROS scavenger, increased normoxic glutathione levels to 1.03 ± 0.06 nmol (mg tissue)^-1 (P < 0.02) and GSH/GSSG ratios to 59.05 ± 5.05 (P < 0.001).
4. NAC (20 µM-10 mM) did not activate or inhibit chemoreceptor cells as it did not alter the normoxic or the hypoxic release of ³H-catecholamines (³H-CAs) from rabbit and calf CBs whose CA deposits had been labelled by prior incubation with the natural CA precursor ³H-tyrosine.
5. NAC (2 mM) was equally ineffective in altering the release of ³H-CAs induced by stimuli (high external K⁺ and ionomycin) that bypass the initial steps of the hypoxic cascade of activation of chemoreceptor cells, thereby excluding the possibility that the lack of effect of NAC on normoxic and hypoxic release of ³H-CAs results from a concomitant alteration of Ca²⁺ channels or of the exocytotic machinery.
6. The present findings do not support the contention that O₂ chemoreception in the CB is linked to variations in the GSH/GSSG quotient as the redox models propose.

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