Ambient O2 Concentration Research Articles

Interactions of nitric oxide and oxygen in cytotoxicity: Proliferation and antioxidant enzyme activities of endothelial cells in culture

Nitric oxide (NO) shows cytotoxicity, and its reaction products with reactive oxygen species, such as peroxynitrite, are potentially more toxic. To examine the role of O2 in the NO toxicity, we have examined the proliferation of cultured human umbilical vein endothelial cells in the presence or absence of NO donor, ((Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl)-amino]diazen-1-ium-1,2-diolate) (DETA-NONOate) (100–500 μM), under normoxia (air), hypoxia (< 0.04% O2) or hyperoxia (88–94% O2). It was found that the dose dependency on NONOate was little affected by the ambient O2 concentration, showing no apparent synergism between the two treatments. We have also examined the effects of exogenous NO under normoxia and hyperoxia on the cellular activities of antioxidant enzymes involved in the H2O2 elimination, since many of them are known to be inhibited by NO or peroxynitrite in vitro. Under normoxia DETA-NONOate (500 μM) caused 25% decrease in catalase activity and 30% increases in glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities in 24 h. Under hyperoxia NO caused about 25% decreases in activities of catalase, glutathione reductase and glucose-6-phosphate dehydrogenase. The H2O2 removal rate by NO-treated cells was computed on the mathematical model for the enzyme system. It was concluded that the cellular antioxidant function is little affected by NO under normoxia but that it is partially impaired when the cells are exposed to NO under hyperoxia.

Glucose deprivation-induced oxidative stress in human tumor cells. A fundamental defect in metabolism?

Recently, glucose deprivation-induced oxidative stress has been shown to cause cytotoxicity, activation of signal transduction (i.e., ERK1, ERK2, JNK, and Lyn kinase), and increased expression of genes associated with malignancy (i.e., bFGF and c-Myc) in MCF-7/ADR human breast cancer cells. These results have led to the proposal that intracellular oxidation/reduction reactions involving hydroperoxides and thiols may provide a mechanistic link between metabolism, signal transduction, and gene expression in these human tumor cells. The current study shows that several other transformed human cell types appear to be more susceptible to glucose deprivation-induced cytotoxicity and oxidative stress than untransformed human cell types. In a matched pair of normal and SV40-transformed human fibroblasts the cytotoxic process is shown to be dependent upon ambient O2 concentration. A theoretical model to explain the results is presented and implications to unifying modern theories of cancer are discussed.

Respiration in bumblebee queens: effect of life phase on the discontinuous ventilation cycle

AbstractEvidence for discontinuous ventilation cycles (DVC) has been obtained for many insects under various experimental conditions. Here, we show that DVC‘s exist for queens of the bumblebee Bombus terrestris in different phases of their life cycle: before entering diapause (pre‐diapause queens) and when a colony has been established (post‐diapause queens). Pre‐ and post‐diapause queens experience distinct environmental conditions (ambient O2 and CO2 concentrations) which is reflected in their DVC: both ventilation frequency and amount of carbon dioxide emitted change with differences in ambient CO2 concentration.

Microbial Consumption of Atmospheric Isoprene in a Temperate Forest Soil

Isoprene (2-methyl-1,3 butadiene) is a low-molecular-weight hydrocarbon emitted in large quantities to the atmosphere by vegetation and plays a large role in regulating atmospheric chemistry. Until now, the atmosphere has been considered the only significant sink for isoprene. However, in this study we performed both in situ and in vitro experiments with soil from a temperate forest near Ithaca, N.Y., that indicate that the soil provides a sink for atmospheric isoprene and that the consumption of isoprene is carried out by microorganisms. Consumption occurred rapidly in field chambers (672.60 +/- 30.12 to 2,718.36 +/- 86.40 pmol gdw day) (gdw is grams [dry weight] of soil; values are means +/- standard deviations). Subsequent laboratory experiments confirmed that isoprene loss was due to biological processes: consumption was stopped by autoclaving the soil; consumption rates increased with repeated exposure to isoprene; and consumption showed a temperature response consistent with biological activity (with an optimum temperature of 30 degrees C). Isoprene consumption was diminished under low oxygen conditions (120 +/- 7.44 versus 528.36 +/- 7.68 pmol gdw day under ambient O(2) concentrations) and showed a strong relationship with soil moisture. Isoprene-degrading microorganisms were isolated from the site, and abundance was calculated as 5.8 x 10 +/- 3.2 x 10 cells gdw. Our results indicate that soil may provide a significant biological sink for atmospheric isoprene.

In VivoExpression of mRNAs Encoding Hypoxia-Inducible Factor 1

Hypoxia-inducible factor 1 (HIF-1) is a heterodimeric basic helix-loop-helix transcription factor that regulates genes whose products play key roles in maintaining O2homeostasis. We have previously demonstrated that HIF-1 mRNA, protein, and DNA-binding activity are induced when mammalian tissue culture cells are subjected to hypoxia. In this paper, we report our analysis of HIF-1 mRNA expressionin vivo.We demonstrate expression of HIF-1α and HIF-1β (ARNT) mRNA in all human, rat, and mouse organs assayed and show for the first time that HIF-1 mRNA expression was induced in brain, kidney, and lung when rats or mice were exposed to reduced ambient O2concentrations for 30 to 60 min. The ubiquitousin vivoexpression of HIF-1α and HIF-1β (ARNT) mRNA is consistent with the proposed role of HIF-1 in coordinating adaptive transcriptional responses to hypoxia.

COMPARISON OF TWO STRATEGIES TO DELIVER OXYGEN IN PRETERM INFANTS. † 1286

With the advent of new technologies, it has become routine to offer supplemental oxygen to neonates via nasal prongs rather than by increasing the ambient oxygen in the incubator. The rationale for use of nasal prongs is that it provides more constant inspired O2 concentration whereas ambient oxygen is subject to fluctuations due to opening of the incubator doors. Nasal prongs, however, have significant disadvantages including i) nasal trauma, ii) increased restlessness, and iii) increased upper airway resistance with increased work of breathing. It remains subject to inspired O2 fluctuation due to prong dislodgement, which is common. Furthermore, we observed substantial clinical improvement in two preterm infants who had fewer apneas and appeared more comfortable after removing the nasal prongs and increasing the ambient O2 concentration. We hypothesized, therefore, that infants would have less apnea, less desaturation and less bradycardia with increased ambient O2 concentration compared with the nasal canulae. To test this hypothesis we studied 8 preterm infants[birthweight 1160±587g (mean ± SE), study weight 1240±534g, gestational age 28±3wk, postnatal age 28 + 4 d] on 9 occasions. Each study consisted of two consecutive 4 hour epochs where FiO2, hypopharyngeal O2, episodes of desaturation 10 s duration were measured while the infant was given O2 by either nasal prongs or into the isolette to maintain saturations at about 95%. Hypopharyngeal FiO2 was measured using a 10F suction catheter inserted via the nares and through which a 60 cc sample of gas was aspirated and its FiO2 measured with a Miniox O2 analyzer. Although hypopharyngeal O2 concentrations were similar (24 ± 4 vs 23 ± 5%, p = 0.55), we observed significantly greater number of apneas 13.2 ± 3 vs 2.8 ± 7 (p < 0.008) and desaturations 14 ± 3 vs 9 ± 3 (p < 0.008) when using nasal prongs. There was no difference in the number of bradycardias. We conclude that administration of O2 into the isolette is associated with fewer apneas and less desaturations and, for this reason, it may be a superior method of O2 administration in preterm infants. Supported by Children's Hospital Research Foundation & Canadian Lung Association.

Ant breathing: testing regulation and mechanism hypotheses with hypoxia

Using normoxic and hypoxic flow-through respirometry, we investigated the regulation of the closed-spiracle (C) and the nature of the fluttering-spiracle (F) phases of the discontinuous gas-exchange cycle (DGC) of the ant Camponotus vicinus. We predicted that as ambient O2 concentrations declined, DGC frequency would increase, because C phase duration would decrease (reflecting earlier hypoxic initiation of the F phase) and F phase duration would shorten (reflecting nitrogen accumulation), if convective mass inflow caused by a negative pressure gradient across the spiracles, rather than by diffusion, is the dominant F phase gas-exchange mechanism. C phase duration decreased with declining ambient O2 concentrations, as predicted. In contrast, DGC frequency decreased and F phase duration increased with decreasing ambient O2 concentrations. This was opposite to the expected trend if gas exchange in the F phase was mediated by convection, as is generally hypothesized. We therefore cannot disprove that F phase gas exchange was largely or purely diffusion-based. In addition, our data show equivalent molar rates of H2O and CO2 emission during the F phase. In contrast, during the open-spiracle phase, the duration of which was not affected by ambient O2 concentration, far more H2O than CO2 was lost. We discuss these findings and suggest that current hypotheses of F phase gas-exchange mechanisms and function in reducing respiratory water loss in adult insects may require revision.

Effect of oxygen on ascorbic acid uptake and concentration in embryonic chick brain.

The effects of oxygen on ascorbic acid concentration and transport were studied in chick embryo (Gallus gallus domesticus). During normoxic incubations, plasma ascorbic acid concentration peaked on fetal day 12 and then fell, before increasing again on day 20 when pulmonary respiration began. In contrast, cerebral ascorbic acid concentration rose after day 6, was maintained at a relatively high level during days 8-18, and then fell significantly by day 20. Exposure of day 16 embryos for 48 h to 42% ambient O2 concentration decreased ascorbic acid concentration by four-fifths in plasma and by one-half in brain, compared to values in normoxic (21% O2) or hypoxic (15% O2) controls. Hyperoxic preincubation of embryos also inhibited ascorbic acid transport, as evidenced by decreased initial rates of saturable and Na(+)-dependent [14C]ascorbic acid uptake into isolated brain cells. It may be concluded that changes in ascorbic acid concentration occur in response to oxidative stress, consistent with a role for the vitamin in the detoxification of oxygen radicals in fetal tissues. However, changing O2 levels have less effect on ascorbic acid concentration in brain than in plasma, indicating regulation of the vitamin by brain cells. Furthermore, the effect of hyperoxia on cerebral vitamin C may result, in part, from inhibition of cellular ascorbic acid transport.

Influence of soil moisture on growth and nitrogen nutrition of alfalfa.

深根性マメ科植物であるアルファルファの生育, 根粒着生および窒素固定能に及ぼす地下水位の影響をポット試験を用いて調査し, さらに土壌気相の酸素濃度との関係を検討した。1) 播種したアルファルファの生育は, 地上部, 地下部とも地下水位が10 cmより高い場合に抑制された。根粒着生や窒素固定能および茎葉部全窒素量は地下水位20 cmの場合でも抑制され, 地下水位の上昇が植物生育よりも窒素固定系に強く抑制的に働くことが明らかとなった。2) 再生植物体に対して地下水位の上昇 (水位10 cm) は再生途中のアルファルファの窒素固定能に顕著な影響を及ぼし, その期間が短時間 (1日) の場合には回復可能であるが, 長期間 (3～5日) の場合には回復不可能であること, および再生植物体の生育, 窒素固定が顕著に低下することを認めた。3) アルファルファの根粒着生, 窒素同定能および単位根粒重当たりの窒素固定能が溶存酸素濃度の低い条件下で顕著に低下することを水耕栽培によって認め, さらに, アルファルファの根粒着生切断根を用いた試験によって単位根粒重当たりの窒素固定能も酸素濃度の低下によって顕著に阻害されることを確かめた。

Partitioning of Noncyclic Photosynthetic Electron Transport to O2-Dependent Dissipative Processes as Probed by Fluorescence and CO2 Exchange

The partitioning of noncyclic photosynthetic electron transport between net fixation of CO(2) and collective O(2)-dependent, dissipative processes such as photorespiration has been examined in intact leaf tissue from Nicotiana tabacum. The method involves simultaneous application of CO(2) exchange and pulse modulated fluorescence measurements. As either irradiance or CO(2) concentration is varied at 1% O(2) (i.e. absence of significant O(2)-dependent electron flow), the quantum efficiency of PSII electron transport (phi(se)) with CO(2) as the terminal acceptor is a linear function of the ratio of photochemical:nonphotochemical fluorescence quenching coefficients (i.e. q(Q):q(NP)). When the ambient O(2) concentration is raised to 20.5% or 42% the q(Q):q(NP) is assumed to predict the quantum efficiency of total noncyclic electron transport (phi'(se)). A factor which represents the proportion of electron flow diverted to the aforementioned dissipative processes is calculated as (phi'(se) - phi(se))/phi'(se) where phi(se) is now the observed quantum efficiency of electron transport in support of net fixation of CO(2). Examination of changes in electron allocation with CO(2) and O(2) concentration and irradiance at 25 degrees C provides a test of the applicability of the Rubisco model to photosynthesis in vivo.

Interaction between hydrogenase, nitrogenase, and respiratory activities in a Frankia isolate from Alnus rubra.

H2 uptake and H2-supported O2 uptake were measured in N2-fixing cultures of Frankia strain ArI3 isolated from root nodules of Alnus rubra. H2 uptake by intact cells was O2 dependent and maximum rates were observed at ambient O2 concentrations. No hydrogenase activity could be detected in NH4+-grown, undifferentiated filaments cultured aerobically indicating that uptake hydrogenase activity was associated with the vesicles, the cellular site of nitrogen fixation in Frankia. Hydrogenase activity was inhibited by acetylene but inhibition could be alleviated by pretreatment with H2. H2 stimulated acetylene reduction at supraoptimal but not suboptimal O2 concentrations. These results suggest that uptake hydrogenase activity in ArI3 may play a role in O2 protection of nitrogenase, especially under conditions of carbon limitation.

Hydrogen Production by Rumen Holotrich Protozoa: Effects of Oxygen and Implications for Metabolic Control by In Situ Conditions

Experiments with washed suspensions of holotrich protozoa (Isotricha spp. and Dasytricha ruminantium) showed that both organisms have an efficient O2-scavenging capability (apparent Km values 2.3 and 0.3 microM, respectively). Reversible inhibition of H2 production increased almost linearly with increasing O2 up to 1.5 microM; higher levels of O2 gave irreversible inhibition. In situ determinations of H2, CH4, O2 and CO2 in ovine rumen liquor, using a membrane inlet mass spectrometer probe, indicated that O2 was present before feeding at 1-1.5 microM and decreased to undetectable levels (less than 0.25 microM) within 25 min after feeding. A transient increase in O2 concentration after feeding occurred only in defaunated animals and resulted in suppression of CH4 and CO2 production. The presence of washed holotrich protozoa decreases the O2 sensitivity of CH4 production by suspensions of a cultured methanogenic bacterium Methanosarcina barkeri. It is concluded that holotrich protozoa play a role in ruminal O2 utilization as well as in the production of fermentation end products (especially short-chain volatile fatty acids) utilized by the ruminant and H2 utilized by methanogenic bacteria. These hydrogenosome-containing protozoa thus both control patterns of fermentation by influencing O2 levels, and are themselves regulated by the low ambient O2 concentrations they experience in the rumen.

DSM-III-R schizotypal personality features and disorder in offspring, siblings and parents of schizophrenic disorder, affective disorder, and normal control parent probands

This chapter describes normalization of embryonic respiration in birds at high altitude. According to Fick's law of diffusion, it can be shown that gaseous exchange at altitude is normalized when the respiratory gas tensions in the air space of an egg are restored to sea level values and when, simultaneously, the partial pressure gradients of O2, CO2, and H2O are reduced in accordance with the increase of the shell conductance. This condition can be achieved by an increase of the ambient O2 and CO2 concentrations, and an increase of relative humidity. A model was calculated for a typical chicken egg weighing 63 g. After 17–19 days of incubation, the O2 consumption of the embryo is 675 ml (STPD)/day. Its CO2 production is 486 ml (STPD)/day and the egg loses 378 mg H2O.day−1. In the air spaces between the inner membrane and the egg shell, the PO2 = 107.7 Torr and the PCO2 = 38.7 Torr. When the same egg is to be incubated at an altitude of 5.5 km, the fractional O2 concentration around the egg must increase to 0.385 and the fractional CO2 concentration to 0.066 to maintain the same gaseous exchange and the same air space gas tensions as at sea level.

Short-term primary culture of mouse interstitial cells: effects of culture conditions of androgen production.

This study examined the effects of culture conditions and hormone treatment on androgen production by mouse interstitial cells in short-term primary culture. Testicular interstitial cells (18-25% 3 beta-hydroxysteriod dehydrogenase-positive) were maintained in serum-free hormone supplemented medium. Basal (nonstimulated) androgen production was found to be plating-density dependent. Androgen production per cell increased dramatically in a time- and cell concentration-dependent manner. This effect was reproduced in low density cultures by addition of charcoal-stripped conditioned medium from high density cultures. The cell anchorage factors, fibronectin and poly-l-lysine, similarly enhanced basal androgen production but did not augment responsiveness to luteinizing hormone (LH). Coating of the culture surface with serum inhibited androgen production. Cultured cells remained responsive to LH for 4 to 5 days and both insulin (5 micrograms/ml) and epidermal growth factor (EGF) (3 ng/ml) augmented LH-stimulated androgen production. There was a transient increase in LH sensitivity and maximum LH-stimulated androgen production for 5 to 72 h in culture followed by a decline in androgen production to low levels after 4 to 5 days in culture. This loss of activity was partially prevented by addition of antioxidants to the medium or by reduction of the ambient O2 concentration to 1%.

Intraparticle effects in char combustion. III transient studies

AbstractUnsteady state mass and energy balance equations along with a probabilistic model to predict the surface area evolution, constitute the model developed to study the dynamics of single particle char combustion. The transients and the ignition‐extinction phenomenon are analyzed with the aid of the pseudo‐steady state structure of the problem. There exists a critical particle size, ambient temperature, ambient oxygen concentration and boundary layer thickness above which the particle ignites. There is an optimum particle size for which the burning time is a minimum. Experimentally observed extinction phenomenon of artificially ignited particles is predicted by the model. Also, it is found that the extinction radius decreases with increase in ambient O2 concentration, which is in qualitative agreement with the experimental results. The model is compared with the simple shrinking core model.

The effects of depressed environmental oxygen tensions on periosteal proliferation of mouse femurs.

SummaryMice subjected to femoral trauma in order to induce periosteal proliferation were exposed to atmospheres of either air, 15% O2 or 10% O2. TDR-3H autoradiographs revealed that 15% ambient O2 concentrations did not markedly affect the periosteal response. Ambient gas concentrations of 10% O2 reduced the labeling index of intact and traumatized femurs only slightly. The decreased ambient concentrations of O2 do not appear to affect the trauma site sufficiently to enhance a local tissue factor capable of stimulating cell proliferation.