Role of Glutathione Redox State in Oxygen Sensing by Carotid Body Chemoreceptor Cells

American Journal of Physiology-Cell Physiology

Sanz-Alfayate²,

Gomez-Niño³

et al. 2009

Self Cite

Carotid body (CB) chemoreceptor cells detect physiological levels of hypoxia and generate a hyperventilation, homeostatic in nature, aimed to minimize the deleterious effects of hypoxia. Intimate mechanisms involved in oxygen sensing in chemoreceptor cells remain largely unknown, but reactive oxygen species (ROS) had been proposed as mediators of this process. We have determined glutathione levels and calculated glutathione redox potential (E(GSH); indicator of the general redox environment of cells) in rat diaphragms incubated in the presence of oxidizing agents of two types: nonpermeating and permeating through cell membranes; in the latter group, unspecific oxidants and inhibitors of ROS-disposing enzymes were used. Selected concentrations of oxidizing agents were tested for their ability to modify the normoxic and hypoxic activity of chemoreceptor cells measured in vitro as their rate of release of neurotransmitters. Results evidence variable relationships between E(GSH) and the activity of chemoreceptor cells. The independence of chemoreceptor cell activity from the E(GSH) would imply that the ability of the CB to play its homeostatic role is largely preserved in any pathological or toxicological contingency causing oxidative stress. Consistent with this suggestion, it was also found that CB-mediated hypoxic hyperventilation was not altered by treatment of intact animals with agents that markedly decreased the E(GSH) in all tissues assayed.

Section: Surgical Proceduresmentioning

confidence: 99%

“…Measurements of GSH and GSSG were made as previously described in detail (17). In brief, spontaneous reduction of 5,5Ј-dithiobis-(2-nitrobenzoic acid) (DTNB) by GSH generates 5-thio-2-nitrobenzoic acid (peak absorbance at 412 nm) and GSSG.…”

Section: Surgical Proceduresmentioning

confidence: 99%

General redox environment and carotid body chemoreceptor function

American Journal of Physiology-Cell Physiology

Sanz-Alfayate²,

Gomez-Niño³

et al. 2009

Self Cite

“…Tissues were dry-blotted on filter paper, weighed and placed in eppendorf tubes with a solution of 5-sulfosalicylic acid (SSA) at 5% containing 0.25 mM EDTA; SSA solution volume was adjusted to 5× tissue weight. Tissues were glass to glass homogenized at 0-4 • C or stored at −80 • C until assay (Gonzalez et al, 2004b). Homogenates were centrifuged (4 • C, 10 min) and the supernatant was used to measure GSH/GSSG.…”

Section: Tissue Incubationmentioning

confidence: 99%

“…The measurement of GSH and GSSG was made with the method of Griffith (1980) as described in detail (Gonzalez et al, 2004b). Spontaneous reduction of 5,5 -dithiobis-(2-nitrobenzoic acid) (DTNB) by GSH generates 5-thio-2-nitrobenzoic acid (TNB; peak absorbance at 412 nm) and GSSG.…”

Section: Gsh and Gssg Assaysmentioning

confidence: 99%

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

Gomez-Niño

Respiratory Physiology & Neurobiology

Obeso

et al. 2009

a b s t r a c tLow 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 (E GSH ) 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 M), antimycin A (0.2 g/ml) and sodium azide (5 mM) decreased E GSH ; NAC restored E GSH 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 E GSH and chemoreceptor cell neurotransmitter release responses and ATP levels. These findings indicate a lack of correlation between mitochondrialgenerated modifications of E GSH 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.

“…Leaving aside considerations on the preparations (isolated mitochondria or the less physiological preparations of isolated particles; see below) and on the methods of ROS measurement (see Gonzalez et al, 2004; see also above), it should be underlined as a fixed rule that when a component (complex) of the respiratory chain is inhibited, all the components of the respiratory chain proximal to the point of inhibition become reduced, with the distal components becoming oxidized, as they would "empty" their electrons into molecular O 2 to form H 2 O. The obvious consequence is that after inhibition of the respiratory chain at a given point, ROS production takes place at the complexes that are proximal to the point of inhibition, because they are the reduced components and therefore they are capable of giving up electrons to O 2 to form O 2 •− .…”

Section: Mitochondriamentioning

confidence: 99%

Chemoreception in the context of the general biology of ROS

González

Respiratory Physiology & Neurobiology

Rocher

et al. 2007

Superoxide anion is the most important reactive oxygen species (ROS) primarily generated in cells. The main cellular constituents with capabilities to generate superoxide anion are NADPH oxidases and mitochondrial respiratory chain. The emphasis of our article is centered in critically examining hypotheses proposing that ROS generated by NADPH oxidase and mitochondria are key elements in O 2 -sensing and hypoxic responses generation in carotid body chemoreceptor cells. Available data indicate that chemoreceptor cells express a specific isoform of NADPH oxidase that is activated by hypoxia; generated ROS acting as negative modulators of the carotid body (CB) hypoxic responses. Literature is also consistent in supporting that poisoned respiratory chain can produce high amounts of ROS, making mitochondrial ROS potential triggers-modulators of the CB activation elicited by mitochondrial venoms. However, most data favour the notion that levels of hypoxia, capable of strongly activating chemoreceptor cells, would not increase the rate of ROS production in mitochondria, making mitochondrial ROS unlikely triggers of hypoxic responses in the CB. Finally, we review recent literature on heme oxygenases from two perspectives, as potential O 2 -sensors in chemoreceptor cells and as generators of bilirubin which is considered to be a ROS scavenger of major quantitative importance in mammalian cells.