Elevated Oxygen Concentration Research Articles

OXYGEN IS UP ON THE SOCIAL SCENE

Imagine sitting in a room where the oxygen is slowly drained out; your first reaction would be to get up and leave as fast as possible. Indeed, an organism's first line of defence when faced with sudden fluctuations in environmental conditions is the hard-wired behavioral response that makes it seek better surroundings. But, what are the sensors in the brain that trigger these behavioral responses? The group of Cornelia Bargmann tackled this fundamental biological question by examining how the model organism, C. elegans, senses oxygen in its environment.Oxygen-sensing is an important feature of most life forms on this planet. Too little oxygen imposes restrictions on the range of tasks an organism can perform; while too much oxygen can have deleterious physiological consequences due to the production of toxic reactive oxygen species.To study the behavior of the 1 mm worm, the team devised a miniature oxygen-gradient chamber with a surface of 5 cm2. The animals avoided oxygen concentrations less than 2% and higher than 12%. With this information in hand, Jesse Gray and the rest of Bargmann's team focused their effort on understanding how the worms avoid high oxygen concentrations.Cyclic GMP (cGMP) is known to play an important role in oxygen-sensing in Drosophila. cGMP is generated from GTP by guanylate cyclases (sGCs)and all guanylate cyclases identified to date are activated by nitric oxide. However, C. elegans seems to lack the enzymes necessary to synthesize nitric oxide, so the team hypothesized that C. elegans guanylate cyclases may be activated by oxygen, instead of nitric oxide, to play a role in oxygen sensing.The first clue that guanylate cyclases in C. elegans could be responsible for oxygen-sensing was that these enzymes are expressed in cells that have a similar morphology to sensory neurons. The team then focused their study on one specific guanylate cyclase, GCY-35. To examine oxygen-sensing behavior in the absence of gcy-35, the group used mutant nematodes in which GCY-35 no longer produced cGMP. The gcy-35 mutants displayed normal hypoxia avoidance, but in contrast to wild-type animals they could not avoid hyperoxia. Similarly, animals that had mutations in the cGMP gated sensory transduction channel were unable to avoid hyperoxic conditions. Since this channel is expressed in the same sensory neurons as GCY-35, it suggests that an oxygen-sensing mechanism through GCY-35 is triggered by cGMP. Importantly, the team showed that the haem domain of GCY-35 displays oxygen-binding characteristics similar to haemoglobin. Together, these results show that GCY-35 acts an oxygen sensor in C. elegans.The group went on to show an even more surprising result, namely that oxygen sensing influences feeding behavior. Laboratory strains of C. elegans are normally kept on agar plates seeded with a bacterial lawn for food. The bacterial lawn naturally creates its own oxygen gradient: the center of the lawn has higher oxygen levels than the thick border. Each C. elegans strain has a tendency to aggregate while feeding and to accumulate at the outer border of the lawn, probably to avoid elevated oxygen concentrations. However, the gcy-35 mutants aggregated and occupied the borders less than wild-type animals. In addition, the feeding behavior of the mutants was unaffected by oxygen concentration contrary to the wild-type animals, which occupied the borders at elevated oxygen concentration but not at low oxygen levels. Therefore, oxygen acts through GCY-35 to regulate social feeding.This work promises to be a significant stepping-stone for comparative physiologists working to understand oxygen-sensing at various levels on the evolutionary scale.

Metabolism‐induced free radical activity does not contribute significantly to loss of viability in moist‐stored recalcitrant seeds of contrasting species

Because recalcitrant seeds are not desiccation‐tolerant they must be stored moist. Their limited storage potential presents significant practical problems, but the cause of viability loss is not known. It has been suggested that a stress‐induced metabolic imbalance can develop during storage that results in free‐radical generation and consequent damage. To investigate this hypothesis, the presence of a stable free radical, lipid peroxidation and representative enzymatic and nonenzymatic protection mechanisms against oxidative attack were monitored in nondormant recalcitrant seeds during moist storage. A comparison was made between seeds of a short‐lived sub‐tropical species (Avicennia marina) and two longer‐lived temperate species (Quercus robur and Castanea sativa). As a test of the hypothesis, seeds of both temperate species were held under conditions of elevated temperature and oxygen concentration to develop different rates of respiration during storage. The number of normal seedlings produced from seeds of the two temperate species declined during storage, but viability remained high, so effects of ageing were not confounded with an increasing proportion of dead seeds in the population. Under these conditions, lipid peroxidation changed little over the storage period, although there was evidence of accumulation of a stable free radical in Q. robur axes. However, this response was not affected by storage conditions that elevated respiration rates. In the shorter‐lived A. marina seeds viability declined soon after the start of storage, but the significant increase in free radicals shown by EPR measurement was only evident when an increasing percentage of the seed population was no longer viable. Changes in the activity of scavenging enzymes and the concentration of antioxidants were time‐dependent and not related to respiration rates. Therefore, in the present work, no consistent evidence was found to show that metabolism‐induced free‐radical activity was a significant contributing factor to pre‐mortem deterioration in moist‐stored recalcitrant seeds.

Influence of Oxygen Concentration on Argon Plasma Coagulation-Induced Tissue Damage in Isolated Pig Tracheas

Background: Argon plasma coagulation (APC) is used during bronchoscopy to restore passage of central airways. Concern has been raised about the possibility that elevated oxygen concentration may increase the tissue damage by APC. Objective: to examine the extent of tissue damage at different concentrations of oxygen in isolated pig tracheas. Methods: The APC-induced tissue damage was investigated macroscopically and microscopically in isolated and artificially ventilated pig tracheas at oxygen concentrations of 21, 50, 75 and 100%. Results: There was deep coagulation of all tissue layers reaching the adventitia independent of the oxygen concentration up to 75% O₂. With 100% O₂, only tissue damage increased and combustion occurred. Conclusions: APC-induced tissue damage in ex vivo pig tracheas was independent of the oxygen concentration relevant for clinical practice.

Temperature stress and oxygen inhibition of nitrogen fixation in a Nostoc cyanobacterium

The effect of elevated temperature and oxygen concentration on nitrogen fixation was investigated in a Nostoc species previously isolated in Java, Indonesia. This organism grows well under nitrogen-fixing conditions at 25°C and also adapts to grow at 40°C. Cells grown at these temperatures responded differently to thermal stress at 48°C; cells grown at 25°C and stressed without oxygen at 48°C were subsequently much more sensitive to oxygen than cells grown at 40°C. This indicates an adaptation of the cells to growth at the higher temperature. In the presence of an adequate supply of CO2, oxygenic photosynthesis in the vegetative cells was not impaired by the thermal stress, nor was whole cell respiration. The addition of H2 substantially overcame the oxygen-inhibition for adapted cells but not for those grown at 25°C. Possible causes of the thermal inactivation of nitrogen fixation are discussed.

Pentane Measurement in Ventilated Infants Using a Commercially Available System

The measurement of breath pentane as a marker of lipid peroxidation has recently been criticized. Problems encountered include the coelution of isoprene with pentane, contamination with exogenous pentane, and the influence of elevated oxygen concentration. The aim of this project was to investigate and evaluate the Chrompack 9001 Gas Chromatograph, using thermal desorption and cryofocussing and an Al 2O 3/KCl PLOT column with FID, for use in the measurement of breath pentane in ventilated preterm infants. We have clearly separated isoprene from n-pentane and used hydrocarbon free air to clear the airways and avoid contamination with exogenous pentane. Samples should be stored in Tedlar bags for a maximum of 48 h and on capped desorption tubes for no longer than 24 h. Patient variability was relatively high (mean 18%, n = 4); thus, all patients were sampled in duplicate. No correlation was found between fractional inspired oxygen concentration (FiO 2) and exhaled pentane in preterm infants ventilated for respiratory distress syndrome. In conclusion, we feel that despite the pitfalls and technical difficulties, with careful attention to detail it is possible to reliably measure breath pentane in ventilated preterm infants as an index of lipid peroxidation. Copyright © 1997 Elsevier Science Inc.

Intraoperative Flash Fires Associated with Disposable Cautery

Three cases of intraoperative flash fires associated with the use of disposable thermal cautery units are described. As opposed to similar reports in the literature, two of the three cases were not associated with an elevated oxygen concentration at the operative site. Precautions in the use of these units or the use of mono- or bipolar cautery units are recommended.

Proportion regulation in Dictyostelium is altered by oxygen

Abstract Submerged cell aggregates of Dictyostelium form the anterior and posterior tissues seen in slugs, but the proportion of the tissues is altered [36]. The proportion of anterior tissue in such aggregates, about twice that found in normal slugs, is due to the elevated oxygen concentration used in submerged cultures. When the oxygen concentration in submerged cultures is reduced to levels similar to that encountered by slugs at an air-water interface, the percentage of anterior tissue is approximately halved. Conversely, raising the atmospheric oxygen concentration surrounding slugs from 21 % to 30% causes a doubling in the proportion of anterior cells. Higher oxygen concentrations cause no further increase. Changes in the pH of the medium, which occur when Dictyostelium is exposed to increased oxygen concentrations, are shown not to affect the proportion of anterior cells. As it is likely that oxygen affects tissue proportions through metabolism, it is suggested that the control of oxygen concentration may be useful in identifying proportion-regulating morphogens.

Potentiating effects of oxygen in lungs damaged by methylcyclopentadienyl manganese tricarbonyl, cadmium chloride, oleic acid, and antitumor drugs

The intraperitoneal administration of methylcyclopentadienyl manganese tricarbonyl (MMT) and cyclophosphamide, exposure to an aerosol of cadmium chloride, intravenous administration of oleic acid, and intratracheal instillation of bleomycin to young female BALB c mice or CD CR rats result in acute lung injury. Pulmonary morphology and lung collagen content were examined in animals treated with these chemicals alone or in combination with an elevated oxygen concentration (80%) in the inspired air. In mice, the development of fibrosis could be significantly enhanced if animals treated with MMT, cadmium chloride, cyclophosphamide, or bleomycin were exposed to 80% oxygen immediately following exposure to these agents. In rats only cyclophosphamide- and bleomycin-induced acute lung injury was potentiated by hyperoxia, resulting in significant enhancement of lung collagen content. The pathogenesis responsible for this differential species response of pulmonary injury to hyperoxia remains to be investigated.

Further Experience With Intragastric Oxygen Measurement to Diagnose H-Type Tracheoesophageal Fistula

In their report on the measurement of elevated intragastric oxygen concentration to detect H-type tracheoesophageal fistula (TEF), Korones and Evans1 mention that they waited two years before reporting their experience in hopes of finding additional cases. We have recently encountered two cases of H-type TEF in which the intragastric oxygen test proved helpful in confirming the diagnosis. CASE REPORTS Case 1 A 1,925-gm girl was born by repeat cesarean section on December 10, 1977, to a 27-year-old gravida 4, para 4 black woman after 34 weeks' gestation. The mother had had a bloody discharge in the second trimester. Membranes ruptured 17 hours before delivery.