Hypoxic responses of Na+/K+ ATPase in trout hepatocytes

Venous valve hypoxia as a possible mechanism of deep vein thrombosis: a scoping review

INTRODUCTION

The pathogenesis of deep vein thrombosis (DVT) has been explained by an interplay between a changed blood composition, vein wall alteration, and blood flow abnormalities. A comprehensive investigation of these components of DVT pathogenesis has substantially promoted our understanding of thrombogenesis in the venous system. Meanwhile, the process of DVT initiation remains obscure. This systematic review aims to collect, analyze, and synthesize the published evidence to propose hypoxia as a possible trigger of DVT.

EVIDENCE ACQUISITION

An exhaustive literature search was conducted across multiple electronic databased including PubMed, EMBASE, Scopus, and Web of Science to identify studies pertinent to the research hypothesis. The search was aimed at exploring the connection between hypoxia, reoxygenation, and the initiation of deep vein thrombosis (DVT). The following key words were used: "deep vein thrombosis," "venous thrombosis," "venous thromboembolism," "hypoxia," "reoxygenation," "venous valve," and "venous endothelium." Reviews, case reports, editorials, and letters were excluded.

EVIDENCE SYNTHESIS

Based on the systematic search outcome, 156 original papers relevant to the issue were selected for detailed review. These studies encompassed a range of experimental and observational clinical research, focusing on various aspects of DVT, including the anatomical, physiological, and cellular bases of the disease. A number of studies suggested limitations in the traditional understanding of Virchow's triad as an acceptable explanation for DVT initiation. Emerging evidence points to more complex interactions and additional factors that may be critical in the early stages of thrombogenesis. The role of venous valves has been recognized but remains underappreciated, with several studies indicating that these sites may act as primary loci for thrombus formation. A collection of studies describes the effects of hypoxia on venous endothelial cells at the cellular and molecular levels. Hypoxia influences several pathways that regulate endothelial cell permeability, inflammatory response, and procoagulation activity, underpinning the endothelial dysfunction noted in DVT.

CONCLUSIONS

Hypoxia of the venous valve may serve as an independent hypothesis to outline the DVT triggering process. Further research projects in this field may discover new molecular pathways responsible for the disease and suggest new therapeutic targets.

N-myc downstream regulated gene 1 (ndrg1) functions as a molecular switch for cellular adaptation to hypoxia

Lack of oxygen (hypoxia and anoxia) is detrimental to cell function and survival and underlies many disease conditions. Hence, metazoans have evolved mechanisms to adapt to low oxygen. One such mechanism, metabolic suppression, decreases the cellular demand for oxygen by downregulating ATP-demanding processes. However, the molecular mechanisms underlying this adaptation are poorly understood. Here, we report on the role of ndrg1a in hypoxia adaptation of the anoxia-tolerant zebrafish embryo. ndrg1a is expressed in the kidney and ionocytes, cell types that use large amounts of ATP to maintain ion homeostasis. ndrg1a mutants are viable and develop normally when raised under normal oxygen. However, their survival and kidney function is reduced relative to WT embryos following exposure to prolonged anoxia. We further demonstrate that Ndrg1a binds to the energy-demanding sodium-potassium ATPase (NKA) pump under anoxia and is required for its degradation, which may preserve ATP in the kidney and ionocytes and contribute to energy homeostasis. Lastly, we show that sodium azide treatment, which increases lactate levels under normoxia, is sufficient to trigger NKA degradation in an Ndrg1a-dependent manner. These findings support a model whereby Ndrg1a is essential for hypoxia adaptation and functions downstream of lactate signaling to induce NKA degradation, a process known to conserve cellular energy.

Nitric oxide synthase (NOS) inhibitor L-NAME activates inducible NOS/NO system and drives multidimensional regulation of Na+ /K+ -ATPase in ionocyte epithelia of immersion-stressed air-breathing fish (Anabas testudineus Bloch)

Nitric oxide (NO) has been implicated in Na⁺  homeostatic control in water-breathing fishes. It is, however, uncertain whether air-breathing fish relies on NO to coordinate Na⁺ /K⁺ -ATPase (NKA)-driven Na⁺  transport during acute hypoxemia. We, thus, examined the action of nitric oxide synthase (NOS) inhibitor, L-NAME on NO availability, inducible NOS (iNOS) protein abundance and the regulatory dynamics of NKA in osmoregulatory epithelia of Anabas testudineus kept at induced hypoxemia. As expected in nonstressed fish, in vivo L-NAME (100 ng g^-1 ) challenge for 30 min declined NO production in serum (40%) and osmoregulatory tissues (average 51.6%). Surprisingly, the magnitude of such reduction was less in hypoxemic fish after L-NAME challenge due to the net gain of NO (average 23.7%) in these tissues. Concurrently, higher iNOS protein abundance was found in branchial and intestinal epithelia of these hypoxemic fish. In nonstressed fish, L-NAME treatment inhibited the NKA activity in branchial and intestinal epithelia while stimulating its activity in renal epithelia. Interestingly in hypoxemic fish, L-NAME challenge restored the hypoxemia-inhibited NKA activity in branchial and renal epithelia. Similar recovery response was evident in the NKAα protein abundance in immunoblots and immunofluorescence images of branchial epithelia of these fish. Analysis of Nkaα1 isoform transcript abundance (Nkaα1a, α1b, α1c) also showed spatial and preferential regulation of Nkaα1 isoform switching. Collectively, the data indicate that L-NAME challenge activates iNOS/NO system in the branchial ionocyte epithelia of hypoxemia-stressed Anabas and demands multidimensional regulation of NKA to restore the Na⁺  transport rate probably to defend against acute hypoxemia.

Hypoxia attenuate ionic transport in the isolated gill epithelium of Carcinus maenas

The gills are osmorespiratory organs of aquatic organisms and the prime target of environmentally induced hypoxia. We have studied the impact of severe hypoxia (0.5 mg O₂/L) on the ionic transport across posterior gills of Carcinus maenas acclimated to 12 ppt seawater (DSW). The short-circuit current (Isc) across hemilamellae from gills i.e. active ion transport was studied in micro Ussing chambers. Hypoxia induced by deoxygenation of the basolateral side, and not the apical side, resulted in time-dependent inhibition of Isc and full recovery of Isc after reoxygenation. Exposure of the crabs to severe 7 h hypoxia decreased the specific activity of Na⁺,K⁺-ATPase in the gills by 36%. Full recovery of enzyme activity occurred in fasted crabs after 3 days of reoxygenation. The intensity of Western blotting bands was not different in the gills of oxygenated, hypoxic and reoxygenated crabs. The reversible, nonspecific blocker of K⁺ channels Cs and hypoxia inhibited over 90% of Isc which is after reoxygenation fully recovered. The specific blocker of Cl^- channels NPPB [5-nitro-2-(3-phenylpropylamino)benzoic acid] blocked Isc by 68.5%. Only the rest of not inhibited Isc in aerated saline was blocked by hypoxia and recovered after reoxygenation. The activity of the antioxidant enzyme catalase was not changed during hypoxia and reoxygenation kept the high enzyme activity in the gills at the level of crabs acclimated to DSW. As a response to hypoxia the presence of 2 mM H₂O₂ induce an initial slight transient decrease of Isc followed by a rise and after reoxygenation fully recovered Isc. Incubation of hemilamellae with the antioxidant derivative Trolox did not affect the inhibition of Isc by hypoxia.

Effect of abiotic and biotic stress factors analysis using machine learning methods in zebrafish

In order to understand the mechanisms underlying stress responses, meta-analysis of transcriptome is made to identify differentially expressed genes (DEGs) and their biological, molecular and cellular mechanisms in response to stressors. The present study is aimed at identifying the effect of abiotic and biotic stress factors, and it is found that several stress responsive genes are common for both abiotic and biotic stress factors in zebrafish. The meta-analysis of micro-array studies revealed that almost 4.7% i.e., 108 common DEGs are differentially regulated between abiotic and biotic stresses. This shows that there is a global coordination and fine-tuning of gene regulation in response to these two types of challenges. We also performed dimension reduction methods, principal component analysis, and partial least squares discriminant analysis which are able to segregate abiotic and biotic stresses into separate entities. The supervised machine learning model, recursive-support vector machine, could classify abiotic and biotic stresses with 100% accuracy using a subset of DEGs. Beside these methods, the random forests decision tree model classified five out of 8 stress conditions with high accuracy. Finally, Functional enrichment analysis revealed the different gene ontology terms, transcription factors and miRNAs factors in the regulation of stress responses.

Cysteine residues 244 and 458-459 within the catalytic subunit of Na,K-ATPase control the enzyme's hydrolytic and signaling function under hypoxic conditions

Our previous findings suggested that reversible thiol modifications of cysteine residues within the actuator (AD) and nucleotide binding domain (NBD) of the Na,K-ATPase may represent a powerful regulatory mechanism conveying redox- and oxygen-sensitivity of this multifunctional enzyme. S-glutathionylation of Cys244 in the AD and Cys 454-458-459 in the NBD inhibited the enzyme and protected cysteines' thiol groups from irreversible oxidation under hypoxic conditions. In this study mutagenesis approach was used to assess the role these cysteines play in regulation of the Na,K-ATPase hydrolytic and signaling functions. Several constructs of mouse α1 subunit of the Na,K-ATPase were produced in which Cys244, Cys 454-458-459 or Cys 244-454-458-459 were replaced by alanine. These constructs were expressed in human HEK293 cells. Non-transfected cells and those expressing murine α1 subunit were exposed to hypoxia or treated with oxidized glutathione (GSSG). Both conditions induced inhibition of the wild type Na,K-ATPase. Enzymes containing mutated mouse α1 lacking Cys244 or all four cysteines (Cys 244-454-458-459) were insensitive to hypoxia. Inhibitory effect of GSSG was observed for wild type murine Na,K-ATPase, but was less pronounced in Cys454-458-459Ala mutant and completely absent in the Cys244Ala and Cys 244-454-458-459Ala mutants. In cells, expressing wild type enzyme, ouabain induced activation of Src and Erk kinases under normoxic conditions, whereas under hypoxic conditions this effect was inversed. Cys454-458-459Ala substitution abolished Src kinase activation in response to ouabain treatment, uncoupled Src from Erk signaling, and interfered with O2-sensitivity of Na,K-ATPase signaling function. Moreover, modeling predicted that S-glutathionylation of Cys 458 and 459 should prevent inhibitory binding of Src to NBD. Our data indicate for the first time that cysteine residues within the AD and NBD influence hydrolytic as well as receptor function of the Na,K-ATPase and alter responses of the enzyme to hypoxia or upon treatment with cardiotonic steroids.

The effects of hypoxia on active ionic transport processes in the gill epithelium of hyperregulating crab, Carcinus maneas

Effects of hypoxia on the osmorespiratory functions of the posterior gills of the shore crab Carcinus maenas acclimated to 12ppt seawater (DSW) were studied. Short-circuit current (Isc) across the hemilamella (one epithelium layer supported by cuticle) was substantially reduced under exposure to 1.6, 2.0, or 2.5mg O₂/L hypoxic saline (both sides of epithelium) and fully recovered after reoxygenation. Isc was reduced equally in the epithelium exposed to 1.6mg O₂/L on both sides and when the apical side was oxygenated and the basolateral side solely exposed to hypoxia. Under 1.6mg O₂/L, at the level of maximum inhibition of Isc, conductance was decreased from 40.0mScm^-2 to 34.7mScm^-2 and fully recovered after reoxygenation. Isc inhibition under hypoxia and reduced ⁸⁶Rb⁺ (K⁺) fluxes across apically located K⁺ channels were caused preferentially by reversible inhibition of basolaterally located and ouabain sensitive Na⁺,K⁺-ATPase mediated electrogenic transport. Reversible inhibition of Isc is discussed as decline in active transport energy supply down regulating metabolic processes and saving energy during oxygen deprivation. In response to a 4day exposure of Carcinus to 2.0mg O₂/L, hemolymph Na⁺ and Cl^- concentration decreased, i.e. hyperosmoregulation was weakened. Variations of the oxygen concentration level and exposure time to hypoxia lead to an increase of the surface of mitochondria per epithelium area and might in part compensate for the decrease in oxygen availability under hypoxic conditions.

Impact of ocean acidification on the hypoxia tolerance of the woolly sculpin, Clinocottus analis

As we move into the Anthropocene, organisms inhabiting marine environments will continue to face growing challenges associated with changes in ocean pH (ocean acidification), dissolved oxygen (dead zones) and temperature. These factors, in combination with naturally variable environments such as the rocky intertidal zone, may create extreme physiological challenges for organisms that are already performing near their biological limits. Although numerous studies have examined the impacts of climate-related stressors on intertidal animals, little is known about the underlying physiological mechanisms driving adaptation to ocean acidification and how this may alter organism interactions, particularly in marine vertebrates. Therefore, we have investigated the effects of decreased ocean pH on the hypoxia response of an intertidal sculpin, Clinocottus analis. We used both whole-animal and biochemistry-based analyses to examine how the energetic demands associated with acclimation to low-pH environments may impact the fish's reliance on facultative air breathing in low-oxygen environments. Our study demonstrated that acclimation to ocean acidification resulted in elevated routine metabolic rates and acid-base regulatory capacity (Na+,K+-ATPase activity). These, in turn, had downstream effects that resulted in decreased hypoxia tolerance (i.e. elevated critical oxygen tension). Furthermore, we present evidence that these fish may be living near their physiological capacity when challenged by ocean acidification. This serves as a reminder that the susceptibility of teleost fish to changes in ocean pH may be underestimated, particularly when considering the multiple stressors that many experience in their natural environments.

Hypoxia Modulates the Swelling-Activated Cl Current in Human Glioblastoma Cells: Role in Volume Regulation and Cell Survival

The malignancy of glioblastoma multiforme (GBM), the most common human brain tumor, correlates with the presence of hypoxic areas, but the underlying mechanisms are unclear. GBM cells express abundant Cl channels whose activity supports cell volume and membrane potential changes, ultimately leading to cell proliferation, migration, and escaping death. In non-tumor tissues Cl channels are modulated by hypoxia, which prompted us to verify whether hypoxia would also modulate Cl channels in GBM cells. Our results show that in GBM cell lines, acute application of a hypoxic solution activates a Cl current displaying the biophysical and pharmacological features of the swelling-activated Cl current (ICl,swell ). We also found that acute hypoxia increased the cell volume by about 20%, and a 30% hypertonic solution partially inhibited the hypoxia-activated Cl current, suggesting that cell swelling and the activation of the Cl current are sequential events. Notably, the hypoxia-induced cell swelling was followed by a regulatory volume decrease (RVD) mediated mainly by ICl,swell . Since, a hypoxia-induced prolonged cell swelling is usually regarded as a death insult, we hypothesized that the hypoxia-activated Cl current could limit cell swelling and prevent necrotic death of GBM cells under hypoxic conditions. In accordance, we found that the ICl,swell inhibitor DCPIB hampered the RVD process, and more importantly it sensibly increased the hypoxia-induced necrotic death in these cells. Taken together, these results suggest that Cl channels are strongly involved in the survival of GBM cells in a hypoxic environment, and may thus represent a new therapeutic target for this malignant tumor. J. Cell. Physiol. 232: 91-100, 2017. © 2016 Wiley Periodicals, Inc.

"Oxygen Sensing" by Na,K-ATPase: These Miraculous Thiols

Control over the Na,K-ATPase function plays a central role in adaptation of the organisms to hypoxic and anoxic conditions. As the enzyme itself does not possess O2 binding sites its "oxygen-sensitivity" is mediated by a variety of redox-sensitive modifications including S-glutathionylation, S-nitrosylation, and redox-sensitive phosphorylation. This is an overview of the current knowledge on the plethora of molecular mechanisms tuning the activity of the ATP-consuming Na,K-ATPase to the cellular metabolic activity. Recent findings suggest that oxygen-derived free radicals and H2O2, NO, and oxidized glutathione are the signaling messengers that make the Na,K-ATPase "oxygen-sensitive." This very ancient signaling pathway targeting thiols of all three subunits of the Na,K-ATPase as well as redox-sensitive kinases sustains the enzyme activity at the "optimal" level avoiding terminal ATP depletion and maintaining the transmembrane ion gradients in cells of anoxia-tolerant species. We acknowledge the complexity of the underlying processes as we characterize the sources of reactive oxygen and nitrogen species production in hypoxic cells, and identify their targets, the reactive thiol groups which, upon modification, impact the enzyme activity. Structured accordingly, this review presents a summary on (i) the sources of free radical production in hypoxic cells, (ii) localization of regulatory thiols within the Na,K-ATPase and the role reversible thiol modifications play in responses of the enzyme to a variety of stimuli (hypoxia, receptors' activation) (iii) redox-sensitive regulatory phosphorylation, and (iv) the role of fine modulation of the Na,K-ATPase function in survival success under hypoxic conditions. The co-authors attempted to cover all the contradictions and standing hypotheses in the field and propose the possible future developments in this dynamic area of research, the importance of which is hard to overestimate. Better understanding of the processes underlying successful adaptation strategies will make it possible to harness them and use for treatment of patients with stroke and myocardial infarction, sleep apnoea and high altitude pulmonary oedema, and those undergoing surgical interventions associated with the interruption of blood perfusion.

Involvement of oxidative stress in hypoxia-induced blood-brain barrier breakdown

The blood-brain barrier (BBB) is a cellular barrier formed by specialized brain endothelial cells under the influence of astrocytes and pericytes. Among the several stress factors known to induce BBB breakdown, hypoxia is probably the most represented but also the least understood. Recent evidence of oxidative stress occurring during hypoxia/ischemia situation raises its possible contribution to barrier breakdown. In this study, we investigated the relevance of oxidative stress in hypoxia-induced barrier disruption. Prolonged hypoxic exposure induced reactive oxygen species (ROS) formation and induced glutathione oxidation. Such effects were accentuated under extreme O(2) deprived environment. Pro-oxidant treatment significantly disrupted barrier function under normal conditions, whereas anti-oxidant treatment contributed to maintain better barrier function and cell survival in an O(2)-reduced environment. In addition, the endothelial response to oxidative stress appeared modulated by the presence of astrocytes and pericytes, thus explaining some of the beneficial contribution of these cells as previously described. Taken together, this study highlights the importance of oxidative stress signaling at the barrier. In addition, cells of the neurovascular compartment differentially modulate ROS levels and also regulate barrier function. Thus, use of reactive oxygen scavengers may be useful to support barrier function following stroke injury.

Species-dependent sensitivity to contaminants: an approach using primary hepatocyte cultures with three marine fish species

There is limited knowledge about the sensitivity of different fish species to environmental pollutants. Such information is pivotal in risk assessment and to understand why some species appear to be more tolerant to contaminants than others. The aim of the current study was to evaluate whether primary hepatocyte cultures of three marine fish species could be established in the field and whether their sensitivity to selected contaminants would differ. Primary hepatocyte cultures of three marine fish species (plaice, long rough dab, Atlantic cod) were established and exposed for 24 h to copper (20-2500 mg L⁻¹) and statins (1-200 mg L⁻¹). Endpoints were esterase activity, metabolic activity and reduced glutathione (GSH) content, all using fluorescent probes. Flatfish hepatocytes were more susceptible to copper and statin exposure than hepatocytes from cod. This study has shown that species-dependent differences in contaminant sensitivity can be investigated using primary hepatocyte cultures.

Mitochondrial respiratory chain activity in an animal model of mania induced by ouabain

OBJECTIVES

Bipolar disorder (BD) is a mental illness associated with higher rates of suicide. The present study aims to investigate the brain mitochondrial respiratory chain activity in an animal model of mania induced by ouabain.

METHODS

Adult male Wistar rats received a single intracerebroventricular administration of ouabain (10-3 and 10-2 M) or vehicle. Locomotor activity was measured using the open field test. Mitochondrial respiratory chain activity was measured in the brain of rats 1 h and 7 days after ouabain administration.

RESULTS

Our results showed that spontaneous locomotion was increased 1 h and 7 days after ouabain administration. Complexes I, III and IV activities were increased in the prefrontal cortex, hippocampus and striatum immediately after the administration of ouabain, at the concentration of 10-3 and 10-2 M. Moreover, complex II activity was increased only in the prefrontal cortex at the concentration of 10-2 M. On the other hand, no significant alterations were observed in complex I activity 7 days after ouabain administration. However, an increase in complexes II, III and IV activities was observed only in the prefrontal cortex at the concentration of 10-2 M.

CONCLUSION

Our findings suggest an increase in the activities of mitochondrial respiratory chain in this model of mania. A possible explanation is that these findings occur as a rebound effect trying to compensate for a decrease of ATP deprivation in BD. The present findings suggest that this model may present good face validity and a limitation in construct validity.

Physiological consequences of gill remodeling in goldfish (Carassius auratus) during exposure to long-term hypoxia

Goldfish (Carassius auratus) acclimated to 7 degrees C and exposed to hypoxia ( approximately 10 mmHg) for 7 days exhibited a pronounced remodeling of the gill consisting of the removal of an interlamellar cell mass (ILCM). Subsequent experiments were designed to assess the impact of gill remodeling and the associated increase in functional lamellar surface area on the distribution of branchial ionocytes and Cl(-) flux across the gill. Despite the increased functional lamellar surface area during hypoxia, there was no corresponding increase in Cl(-) loss or efflux of the extracellular marker polyethylene glycol (PEG 4000). However, when hypoxic fish were returned to normoxic water for 12 h, rates of Cl(-) and PEG efflux were markedly stimulated in keeping with an increased surface area for solute movement. Similarly, the rate of branchial Cl(-) uptake was reduced (105 +/- 22 vs. 45 +/- 8 micromol x kg(-1) x h(-1)) in normoxic and hypoxic fish, respectively, but then stimulated (345 micromol x kg(-1) x h(-1)) upon reestablishment of normoxic conditions. Hypoxia (7 days) was accompanied by a significant decrease in the total cross-sectional area of branchial ionocytes owing to a decrease in their numbers and individual sizes. Thus, despite experiencing an increase in functional lamellar surface area, hypoxic goldfish limit branchial Cl(-) loss likely by a hypoxia-mediated decrease in paracellular permeability. In normoxic fish, the ionocytes were largely confined to the outer edges of the ILCM. During hypoxia, preexisting ionocytes migrated with the shrinking ILCM, while a smaller proportion of newly differentiated cells appeared below the surface of the ILCM. The capacity to maintain a population of ionocytes in contact with the water is an appropriate strategy to retain ionoregulatory capabilities regardless of whether the lamellae are uncovered or covered.

Moderate altitude but not additional endurance training increases markers of oxidative stress in exhaled breath condensate

Oxidative stress occurs at altitude, and physical exertion might enhance this stress. In the present study, we investigated the combined effects of exercise and moderate altitude on redox balance in ten endurance exercising biathletes, and five sedentary volunteers during a 6-week-stay at 2,800 m. As a marker for oxidative stress, hydrogen peroxide (H(2)O(2)) was analyzed by the biosensor measuring system Ecocheck, and 8-iso prostaglandin F2alpha (8-iso PGF2alpha) was determined by enzyme immunoassay in exhaled breath condensate (EBC). To determine the whole blood antioxidative capacity, we measured reduced glutathione (GSH) enzymatically using Ellman's reagent. Exercising athletes and sedentary volunteers showed increased levels of oxidative markers at moderate altitude, contrary to our expectations; there was no difference between both groups. Therefore, all subjects' data were pooled to examine the oxidative stress response exclusively due to altitude exposure. H(2)O(2) levels increased at altitude and remained elevated for 3 days after returning to sea level (p < or = 0.05). On the other hand, 8-iso PGF2alpha levels showed a tendency to increase at altitude, but declined immediately after returning to sea level (p < or = 0.001). Hypoxic exposure during the first day at altitude resulted in elevated GSH levels (p < or = 0.05), that decreased during prolonged sojourn at altitude (p < or = 0.001). In conclusion, a stay at moderate altitude for up to 6 weeks increases markers of oxidative stress in EBC independent of additional endurance training. Notably, this oxidative stress is still detectable 3 days upon return to sea level.

Oxygen-induced Regulation of Na/K ATPase in cerebellar granule cells

Adjustment of the Na/K ATPase activity to changes in oxygen availability is a matter of survival for neuronal cells. We have used freshly isolated rat cerebellar granule cells to study oxygen sensitivity of the Na/K ATPase function. Along with transport and hydrolytic activity of the enzyme we have monitored alterations in free radical production, cellular reduced glutathione, and ATP levels. Both active K(+) influx and ouabain-sensitive inorganic phosphate production were maximal within the physiological pO(2) range of 3-5 kPa. Transport and hydrolytic activity of the Na/K ATPase was equally suppressed under hypoxic and hyperoxic conditions. The ATPase response to changes in oxygenation was isoform specific and limited to the alpha1-containing isozyme whereas alpha2/3-containing isozymes were oxygen insensitive. Rapid activation of the enzyme within a narrow window of oxygen concentrations did not correlate with alterations in the cellular ATP content or substantial shifts in redox potential but was completely abolished when NO production by the cells was blocked by l-NAME. Taken together our observations suggest that NO and its derivatives are involved in maintenance of high Na/K ATPase activity under physiological conditions.

Hypoxia-related lipid peroxidation: Evidences, implications and approaches

Hypoxia may be intensified by concurrent oxidative stress. Lack of oxygen in relation to aerobic ATP requirements, as hypoxia has been defined, goes along with an increased generation of reactive oxygen species (ROS). Polyunsaturated fatty acids (PUFAs) range among the molecules most susceptible to ROS. Oxidative breakdown of n-3 PUFAs may compromise not only membrane lipid matrix dynamics, and hence structure and function of membrane-associated proteins like enzymes, receptors, and transporters, but also gene expression. Eicosapentaenoic acid depletion, products of lipid peroxidation (LP), as well as, lack of oxygen may combine in exacerbating activity of nuclear factor kappa B (NFkappaB), an ubiquitous pro-inflammatory and anti-apoptotic transcription factor. Field studies at high altitude show malondialdehyde (MDA) content in exhaled breath condensate (EBC) of mountaineers to correlate with Lake Louis score of acute mountain sickness. A pathogenic role of LP in hypoxia can therefore be expected. By control of LP, some species seem to cope more efficiently than others with naturally occurring hypoxia. Limitation of potential pro-inflammatory effects of hypoxia-related LP by an adequate provision of n-3 PUFAs and antioxidants may contribute to increase survival under conditions where oxygen is lacking in relation to aerobic ATP requirements. A need for antioxidant intervention, however, should be weighed against the ROS requirement for triggering adaptive processes in response to an increased demand of oxygen.

Effects of acclimation and incubation temperature on the glutathione antioxidant system in killifish and RTH-149 cells

Glutathione (GSH) is an important antioxidant that is involved in a multitude of cellular processes. However, in fish, GSH levels, turnover, and activity of associated enzymes are low when compared to those of mammals. To determine whether temperature influences the GSH antioxidant system in fish, and can explain the differences in GSH between fish and mammals, we examined the effects of acclimation temperature on total GSH (tGSH) levels and apparent half-life (as an estimate of turnover) in a rainbow trout hepatoma cell line (RTH-149), and GSH levels, and glutathione peroxidase (GPx) and reductase (GR) activity in the eurythermal killifish. Increasing incubation temperature decreased half-life and transiently increased levels of tGSH in RTH-149 cells. In killifish, increased acclimation temperature increased tGSH levels in the liver, brain and muscle, and increased hepatic GPx and GR activities. When the relationships between temperature and GSH half-life, levels and enzyme activity were extrapolated to 37 degrees C, temperature could only partially accounted for differences in the GSH antioxidant system in fish compared to mammals. The differences in the GSH antioxidant system between fish and mammals may not be solely due to temperature effects, but also to the increased metabolic cost of endothermy in mammals.

Rapid regulation of Na+ fluxes and ammonia excretion in response to acute environmental hypoxia in the Amazonian oscar, Astronotus ocellatus

The Amazonian oscar is extremely resistant to hypoxia, and tolerance scales with size. Overall, ionoregulatory responses of small ( approximately 15 g) and large oscars ( approximately 200 g) to hypoxia were qualitatively similar, but the latter were more effective. Large oscars exhibited a rapid reduction in unidirectional Na(+) uptake rate at the gills during acute hypoxia (Po(2) approximately 10 mmHg), which intensified with time (7 or 8 h); Na(+) efflux rates were also reduced, so net balance was little affected. The inhibitions were virtually immediate (1st h) and preceded a later 60% reduction (at 3 h) in gill Na(+)-K(+)-ATPase activity, reflected in a 60% reduction in maximum Na(+) uptake capacity without change in affinity (Km) for Na(+). Upon acute restoration of normoxia, recovery of Na(+) uptake was delayed for 1 h. These data suggest that dual mechanisms may be involved (e.g., immediate effects of O(2) availability on transporters, channels, or permeability, slower effects of Na(+)-K(+)-ATPase regulation). Ammonia excretion appeared to be linked indirectly to Na(+) uptake, exhibiting a Michaelis-Menten relationship with external [Na(+)], but the Km was less than for Na(+) uptake. During hypoxia, ammonia excretion fell in a similar manner to Na(+) fluxes, with a delayed recovery upon normoxia restoration, but the relationship with [Na(+)] was blocked. Reductions in ammonia excretion were greater than in urea excretion. Plasma ammonia rose moderately over 3 h hypoxia, suggesting that inhibition of excretion was greater than inhibition of ammonia production. Overall, the oscar maintains excellent homeostasis of ionoregulation and N-balance during severe hypoxia.

Metabolic and ionoregulatory responses of the Amazonian cichlid, Astronotus ocellatus, to severe hypoxia

We examined the metabolic and ionoregulatory responses of the Amazonian cichlid, Astronotus ocellatus, to 20 h exposure to severe hypoxia (0.37 +/- 0.19 mg O(2)/l; 4.6% air saturation) or 8 h severe hypoxia followed by 12 h recovery in normoxic water. During 20 h exposure to hypoxia, white muscle [ATP] was maintained at normoxic levels primarily through a 20% decrease in [creatine phosphate] (CrP) and an activation of glycolysis yielding lactate accumulation. Muscle lactate accumulation maintained cytoplasmic redox state ([NAD(+)]/[NADH]) and was associated with an inactivation of the mitochondrial enzyme pyruvate dehydrogenase (PDH). The inactivation of PDH was not associated with significant changes in cytoplasmic allosteric modulators ([ADP(free)], redox state, or [pyruvate]). Hypoxia exposure caused an approximately 65% decrease in gill Na(+)/K(+) ATPase activity, which was not matched by changes in Na(+)/K(+) ATPase alpha-subunit protein abundance indicating post-translational modification of Na(+)/K(+) ATPase was responsible for the decrease in activity. Despite decreases in gill Na(+)/K(+) ATPase activity, plasma [Na(+)] increased, but this increase was possibly due to a significant hemoconcentration and fluid shift out of the extracellular space. Hypoxia caused an increase in Na(+)/K(+) ATPase alpha-subunit mRNA abundance pointing to either reduced mRNA degradation during exposure to hypoxia or enhanced expression of Na(+)/K(+) ATPase alpha-subunit relative to other genes.

Oxygen availability regulates metabolism and gene expression in trout hepatocyte cultures

We studied the metabolic rate, cellular energetic state, hypoxia-inducible factor-1 (HIF-1) activation, and expression of enzymes involved in energy metabolism using rainbow trout (Oncorhynchus mykiss) hepatocytes over the oxygen range from 21 to 1 kPa. Oxygen dependence of these factors was assessed by gradually reducing oxygen supply to cells from 21 kPa to 10, 5, 2, and 1 kPa. Moreover, time course experiments for up to 20 h at oxygen tensions of 1 and 2 kPa were carried out. Reduction of oxygen from 21 kPa to 10, 5, 2, and 1 kPa decreased metabolic rate of the cells by 14, 24, 37, and 46%, respectively. This response was instantaneous and fully reversible upon reoxygenation. Cellular ATP content and the expression of all mRNAs studied decreased when oxygen was reduced from 21 to 5 and 2 kPa. The lowest ATP levels, approximately 43% of the initial value, were measured at 5 kPa of oxygen, whereas the reduction in mRNA amounts was most pronounced at 2 kPa. At 1 kPa oxygen tension, both ATP content and mRNA amounts returned to normoxic (21 kPa) levels with a concomitant activation of HIF-1, indicating reorganization of energy metabolism in adaptation of cells to low oxygen supply. These results show that oxygen has a direct regulatory effect on metabolism of trout hepatocyte cultures, supporting the view that oxygen has a profound role in metabolic regulation in cells.

Glycine intravenous donor preconditioning is superior to glycine supplementation to low-potassium dextran flush preservation and improves graft function in a large animal lung transplantation model after 24 hours of cold ischemia

OBJECTIVES

The potential role of glycine in combination with standard lung preservation with low-potassium dextran solution in lung ischemia-reperfusion injury has not been investigated in a preclinical porcine transplant model.

METHODS

In a control group (n = 6), donor lungs were flushed with 1 liter of low-potassium dextran solution. In a second group (LPD-glyc, n = 6), low-potassium dextran solution was supplemented with 3.75 g of glycine. In a third group (IV-glyc, n = 6), donor preconditioning was performed by intravenous administration of 3.75 g glycine 1 hour before low-potassium dextran preservation. Grafts were stored in low-potassium dextran at 4 degrees C for 24 hours. Posttransplant graft function was assessed throughout a 7-hour observation period.

RESULTS

In the control group, 2 recipients died of right-sided heart failure caused by severe ischemia-reperfusion injury. All animals of the glycine groups survived the entire observation period. Pulmonary vascular resistance remained significantly (P < .01) lower in both glycine groups when compared with controls. At the end of the observation period pulmonary vascular resistance in the control group was higher (P < .01) compared with the glycine groups (1310 +/- 319 dyn x sec x cm(-5) vs 879 +/- 127 dyn x sec x cm(-5) [LPD-glyc] vs 663 +/- 191 dyn x sec x cm(-5) [IV-glyc]). Changes of lung tissue water content were lower in the IV-glyc group compared with the LPD-control (P < .01) and LPD-glyc lungs (P < .05). Oxygenation (PO2/FiO2) was higher in the IV-glyc group compared with the LPD-glyc and control lungs (445 +/- 110 mm Hg vs 388 +/- 124 mm Hg [P < .01] vs 341 +/- 224 mm Hg [P < .001], respectively).

DISCUSSION

Modification of low-potassium dextran solution with glycine or donor preconditioning ameliorates ischemia-reperfusion injury in lung transplantation. This intriguing approach merits further evaluation with respect to the mechanisms involved and may improve results in clinical lung preservation.

Na-K-ATPase in rat cerebellar granule cells is redox sensitive

Redox-induced regulation of the Na-K-ATPase was studied in dispersed rat cerebellar granule cells. Intracellular thiol redox state was modulated using glutathione (GSH)-conjugating agents and membrane-permeable ethyl ester of GSH (et-GSH) and Na-K-ATPase transport and hydrolytic activity monitored as a function of intracellular reduced thiol concentration. Depletion of cytosolic and mitochondrial GSH pools caused an increase in free radical production in mitochondria and rapid ATP deprivation with a subsequent decrease in transport but not hydrolytic activity of the Na-K-ATPase. Selective conjugation of cytosolic GSH did not affect free radical production and Na-K-ATPase function. Unexpectedly, overloading of cerebellar granule cells with GSH triggered global free radical burst originating most probably from GSH autooxidation. The latter was not followed by ATP depletion but resulted in suppression of active K(+) influx and a modest increase in mortality. Suppression of transport activity of the Na-K-ATPase was observed in granule cells exposed to both permeable et-GSH and impermeable GSH, with inhibitory effects of external and cytosolic GSH being additive. The obtained data indicate that redox state is a potent regulator of the Na-K-ATPase function. Shifts from an "optimal redox potential range" to higher or lower levels cause suppression of the Na-K pump activity.