Low O2 Partial Pressure Research Articles

Further evidence implicating a cytochrome P-450-mediated reaction in the contractile tension of the lamb ductus arteriosus.

The authors have recently provided evidence implicating the cytochrome P-450 system in the generation of contractile tension of the ductus arteriosus. To confirm this possibility, carbon monoxide (CO/O2 ratio, 0.27) and cytochrome P-450 inhibitors [4-phenylimidazole; 14-isocyano,15-(methoxymethyleneoxy)-5Z,8Z,11 Z-eicosatrienoic acid; 9-hydroxyellipticine; alpha-naphthoflavone] were tested on the isolated ductus arteriosus from mature fetal lambs equilibrated at low (4-26 mm Hg) or high (229-694 mm Hg) O2 partial pressure (PO2). Carbon monoxide completely relaxed intact vessel wall preparations and preparations consisting of only the muscle. Carbon monoxide relaxation was reversed by illumination with monochromatic light and the peak for the photoactivated contraction occurred at 450 nm. 4-Phenylimidazole (100 and 1,000 microM) was also a relaxant agent, and its action was manifest at both low and high PO2. Unlike 4-phenylimidazole, the isonitrile compound (5 microM) and 9-hydroxyellipticine (10 and 100 microM) were relaxant only at low PO2 and were also less potent. At the same PO2, alpha-naphthoflavone (10 microM) barely reduced ductal tension. Treatment of the ductus with either a combination of superoxide dismutase (60 or 150 U/ml) and catalase (40 or 1,000 U/ml) or mannitol alone (80 mM) failed to alter the steady-state tone at low PO2 and the contractile response to O2. Arachidonic acid was tested on tissues pretreated with the dual cyclooxygenase and lipoxygenase inhibitor, BW755C (10 microM), and produced a weak relaxation at a concentration of 1 microM or higher. 5,6-Epoxytrienoic acid relaxed the untreated tissue, and its action was abolished by indomethacin (2.8 microM).(ABSTRACT TRUNCATED AT 250 WORDS)

Characteristics of a nitrogen-fixing methanotroph, Methylocystis T-1.

A methane-oxidizing bacterium capable of nitrogen fixation was isolated from soil taken from an area which leaked methane gas. Strain T-1 was a catalase and oxidase-positive, gram-negative straight rod-shaped strictly aerobic bacterium which formed lipid cysts and type II intracytoplasmic membranes. The organism was a microaerophilic nitrogen-fixing methanotroph. Strain T-1 is considered to be classified into Methylocystis. The organism evolved hydrogen gas when grown in the nitrogen-free medium of atmospheric oxygen concentrations of 1.5% or more. Below this level, however, hydrogen gas was not evolved. In addition to methanol, formaldehyde and formate, ethanol, acetate and hydrogen gas served as oxidizable substrates for the acetylene reduction test. H2-stimulated nitrogenase activity was limited in a very narrow range of oxygen concentration and not detected at 2% O2. With acetate as the substrate, however, about an 80% of the maximum acetylene reduction activity was detected at 2% O2. These results suggest that strain T-1 is capable of recycling the hydrogen gas evolved during nitrogen fixation under low partial pressures of O2.

Structure of α-Fe2O3 single crystal surfaces following Ar+ ion bombardment and annealing in O2

The surface stoichiometry and structure of α-Fe2O3(0001) and (10ovbar|12) natural growth faces has been studied with X-ray photoemission and LEED following room temperature Ar ion bombardment and subsequent annealing in partial pressures of O2 between 400°C and 1000°C. Disordered, oxygen-deficient ion bombardment surfaces were annealed to produce surface structures and stoichiometries approaching the ideal truncation of bulk α-Fe2O3, but only after long, high temperature annealing treatments in 10−6 Torr O2. LEED suggests that a Fe3O4(111) layer initially forms on the (0001) face for annealing temperatures up to 775°C. At higher temperatures, extra diffraction beams are observed which are attributed to multiple scattering across a Fe1−xO(111)/α-Fe2O3(0001) interface. The extra beams disappear after long annealing times at 900°C and are replaced by a (1 × 1) pattern characteristic of α-Fe2O3(0001). On the (10ovbar|12) surface, a (1 × 1) LEED pattern is observed when the surface is annealed in 10−6 Torr O2, but a (1 × 2) reconstruction similar to that observed on the surface of α-Al2O3 is evident in lower O2 partial pressures. The surface phases produced by ion bombardment and annealing treatments are quite different from those predicted by the bulk FeO phase diagram.

ChemInform Abstract: The Oxygen Partial Pressure Dependence of the Defect Structure of Chromium(III) Oxide

Abstracthas been investigated in the temp. range 1000‐1800 K. At low O2 partial pressures, Cr2O3 behaves as n‐type semiconductor, whereas the material is p‐type at high O2 partial pressures.

Gas exchange studies in two Portuguese grapevine cultivars

Gas exchange characteristics of leaves of Vitis vinifera L. cvs Tinta Amarela and Periquita, two grapevine cultivars grown in distinct climatic regions of Portugal, were studied under natural and controlled conditions. Daily time courses of gas exchange were measured on both a hot, sunny day and a cooler, partly cloudy day. Responses of net photosynthesis to irradiance and internal partial pressure of CO2, were also obtained. A strong correlation between net photosynthesis (PN) and leaf conductance (gs) was found during the diurnal time courses of gas exchange, as well as a relatively constant internal partial pressure of CO2 (Pi), even under non‐steady‐state conditions. On the cloudless day, both PN and gs were lower in the afternoon than in the morning, despite similar conditions of leaf temperature, air to leaf water vapor deficit and irradiance. The response curves of net photosynthesis to internal CO2 showed linearity up to pi values of 50 Pa, possibly indicating a substantial excess of photosynthetic capacity. When measured at low partial pressures of O2 (1 kPa), PN became inhibited at high CO2 levels. Inhibition of PN at high CO2 was absent under normal levels of O2 (21 kPa). Significant differences in gas exchange characteristics were found between the two cultivars, with T. Amarela having higher rates under similar measurement conditions. In particular, the superior performance of T. Amarela at high temperatures may represent adaptation to the warmer conditions at its place of origin.

Function of myoglobin in oxygen consumption by isolated perfused fish hearts.

Myoglobin, an intracellular O2-binding protein, plays a protective role in maintaining performance of isolated fish hearts under hypoxic conditions. This study was designed to test the hypothesis that the protein contributes to O2 consumption under conditions of increased O2 demand or hypoxia. Isolated myoglobin-rich sea raven (Hemitripterus americanus) hearts and myoglobin-poor ocean pout (Macrozoarces americanus) hearts were perfused under conditions of changing partial pressure of O2 (PO2) and afterload. Sea raven hearts maintained O2 consumption and cardiac performance at low PO2 and high afterload, whereas ocean pout hearts did not. In other cases sea raven and ocean pout hearts were treated with hydroxylamine, which renders myoglobin incapable of binding O2, and subjected to changing PO2 and afterload. Sea raven hearts could not maintain O2 consumption and cardiac performance, whereas hydroxylamine treatment had no effect on O2 consumption in ocean pout hearts under these conditions. These data provide the first evidence to support the concept that myoglobin plays a role in O2 consumption of hearts.

Respiratory Gas Tensions and Gas Exchange in Active and Dormant Land Snails, Otala lactea

The respiration physiology of active and dormant land snails was examined in relation to the reduced rates of metabolism and water loss that occur during dormancy. In active snails, partial pressures of O₂ (PO₂) and of CO₂ (PCO₂) in the lung differed by less than 16 torr from air. Arterial PCO₂ was similar to that in lung gas, but arterial PO₂ was as much as 60 torr lower than that in the lung, indicating strong diffusion limitation of O₂ uptake across the lung epithelium. With increase in temperature, PCO₂ increased and PO₂ decreased in the lung, and hemolymph pH declined. During dormancy, mean PO₂ in the lung was 100 torr lower and mean PCO₂ was 50 torr higher than during activity. PO₂ dropped as low as 2.6 torr and PCO₂ rose as high as 101.0 torr. Low PO₂ and high PCO₂ in the lung and hemolymph were associated with low O₂ consumption and also with low values of the respiratory exchange ratio (RE), indicating that CO₂ accumulates when O₂ consumption is reduced. Most respiratory CO₂ was released during relatively infrequent periods of high RE and rapid gas exchange. Reduced metabolic rate, high PCO₂, and low PO₂ in the lung are shown to be related to the low rate of evaporative water loss characteristic of dormancy.

Growth characteristics of non-heterocystous cyanobacterium Plectonema boryanum with N2 as nitrogen source

Strains of filamentous, non-heterocystous cyanobacteria from the Pasteur Culture Collection (PCC), able to synthesize nitrogenase under anaerobic test conditions, were tested for growth with N2 as sole nitrogen source at low O2 partial pressure (less than 0.05%).

The crucial role of low steady state oxygen partial pressures in haloalkane free-radical-mediated lipid peroxidation: Possible implications in haloalkane liver injury

It is well established that the hepatotoxicity of the completely halogenated alkanes CCI, and CBrC13 is closely linked to their reductive activation to freeradicals catalyzed by cytochrome P-450, the terminal oxidase of the hepatic microsomal mixed function oxidase system. Damage to cellular components may result either from a direct attack of the haloalkane free-radicals or from lipid peroxidation initiated by interaction of the free-radicals with unsaturated fatty acids of membrane phospholipids (see [l-4] for recent reviews). The inactivation of cytochrome P-450 itself, possibly due to covalent binding of haloalkane radicals to the haem moiety of the cytochrome, is an example of direct damage 15-81 while the inactivation of the microsomal enzymes glucose6-phosphatase and UDPglucuronyl-transferase, as well as the loss of latent activity of microsomal nucleoside ~phosphatase [P-13] exemplify damage arising from lipid peroxidation. The completely halogenated compounds CCll and CBrCls are metabolized by cytochrome P-450 solely by reduction. In contrast, those haioalkanes containing a hydrogen atom in their molecule are also oxidatively metabolized by cytochrome P-450 by hydroxylation of the carbon-hydrogen bond. From haloforms such as CHBr3 and CHCls the respective dihalocarbonyl compounds are formed by elimination of a proton and a halide ion, and it is assumed that their formation is responsible for the hepatotoxicity of these halomethanes [14-181. In the case of the anaesthetic CFsCHBrCl (halothane) the oxidative degradation to the stable end product trifluoroacetic acid [19,20] is generally believed to be part of its detoxication pathway 12,213; even though there is evidence that it may also be involved in an immunolo~cal mechanism of halothane liver injury [22]. The subject of the present paper is the haloalkane free-radical-mediated lipid peroxidation and, in particular, the crucial role of low steady state O2 partial pressures (Po2) in this potent destructive process. First, the theoretical background is given which led us to postulate that low steady state PO2 are decisive for haloalkane free-radical-mediated lipid peroxidation. Subsequently, the experimental set-up is described which was utilized to validate this postulate and experiments with liver microsomes and isolated liver ceils are shown which demonstrate that the postulate is generahy applicable to polyhalogenated alkanes. Finally, possible implications in haloalkane liver injury are discussed.

Oxides formed on polycrystalline titanium thin-film surfaces: rates of formation and composition of oxides formed at low and high O2 partial pressures

Oxides formed on polycrystalline titanium thin-film surfaces: rates of formation and composition of oxides formed at low and high O2 partial pressures

Low P50 in deer mice native to high altitude.

Whereas it is widely believed that animals native to high altitude show lower O2 partial pressures at 50% hemoglobin saturation (P50) than do related animals native to low altitude, that "fact" has not been well documented. Consequently, P50 at pH 7.4, PCO2(7.4), the CO2 Bohr effect, and the buffer slope (delta log PCO2/delta pH) were determined via the mixing technique in Peromyscus maniculatus native to a range of altitudes but acclimated to 340 or 3,800 m. PCO2(7.4) and buffer slope were substantially lower at high altitude. The change in P50(7.4) between acclimation altitudes was minimal (0.8% increase at 3,800 m), because of counterbalancing changes in PCO2, 2,3-diphospho-D-glycerate concentration, and perhaps other factors. At both acclimation altitudes there was a highly significant negative correlation between P50(7.4) and native altitude. Since pH in vivo probably increases slightly at high altitude, the data on P50 corrected to pH 7.4 are probably underestimates of the difference in in vivo P50 at low vs. high altitude. Hence these results corroborate theoretical predictions that low P50 is advantageous under severe hypoxic stress.

Nitrous oxide production from nitrification and denitrification in marine sediment at low oxygen concentrations

Measurements of N2O production (release of free N2O), nitrification, and denitrification were made simultaneously in NH4Cl- and KNO3-amended suspensions of marine sediment. An open flow system was designed for the application of low partial pressures of O2 (0–10 kPa) to the sediment. The overall rate of N2O production increased dramatically at the lowest O2 tensions (0–0.2 kPa) and had a maximum at complete anoxia. The specific rates of N2O production from nitrification (N2On) and from denitrification (N2Od) were determined after separation of the processes with inhibitors. Within the range of 0–0.2 kPa O2, the rate of N2On production showed an apparent maximum of 0.1 kPa O2 where the production accounted for 25% of the total activity of nitrification ([Formula: see text] oxidation). The rate of N2Od production, however, continued to increase as the O2 fell to zero. The proportion of N2Od to the total N2Od plus N2 produced from denitrification increased at the higher O2 tensions and reached the maximum of about 50% at 5 kPa O2. Except for a narrow range between 0.1 and 0.2 kPa O2, denitrification was the main source of N2O at 0–10 kPa O2.

Cytochrome P 450-linked monooxygenase: involvement in the lamb ductus arteriosus.

CO and metyrapone were tested on isolated ductus arteriosus preparations from mature fetal lambs equilibrated at low (4-12 Torr) and high (511-712 Torr) O2 partial pressure (PO2). CO completely reversed the contractile tension of the ductus at either PO2 value and was equally effective in the absence and presence of indomethacin. CO relaxation still occurred when the tissue was exposed to a gas mixture having a CO-to-O2 ratio of 0.27. The inhibitory effect of CO on the O2-contracted ductus was variably reversed by light. Metyrapone was also a relaxant agent, and its action was greater at low than at high PO2. Unlike the lamb ductus, the O2-constricted guinea pig ductus did not respond to CO (maximum CO-to-O2 ratio around 1), whereas it was relaxed by metyrapone. These findings implicate a cytochrome P450-catalyzed enzymic process in the maintenance of muscle tone of the lamb ductus arteriosus and in the contractile response of the vessel to O2.

Barometric pressures at extreme altitudes on Mt. Everest: physiological significance.

Barometric pressures were measured on Mt. Everest from altitudes of 5,400 (base camp) to 8,848 m (summit) during the American Medical Research Expedition to Everest. Measurements at 5,400 m were made with a mercury barometer, and above this most of the pressures were obtained with an accurate crystal-sensor barometer. The mean daily pressures were 400.4 +/- 2.7 (SD) Torr (n = 35) at 5,400 m, 351.0 +/- 1.0 Torr (n = 16) at 6,300 m, 283.6 +/- 1.5 Torr (n = 6) at 8,050 m, and 253.0 Torr (n = 1) at 8,848 m. All these pressures are considerably higher than those predicted from the ICAO Standard Atmosphere. The chief reason is that pressures at altitudes between 2 and 16 km are latitude dependent, being higher near the equator because of the large mass of cold air in the stratosphere of that region. Data from weather balloons show that the pressure at the altitude of the summit of Mt. Everest varies considerably with season, being about 11.5 Torr higher in midsummer than in midwinter. Although the mountain has been climbed without supplementary O2, the very low O2 partial pressure at the summit means that it is at the limit of man's tolerance, and even day-by-day variations in barometric pressure apparently affect maximal O2 uptake.

Interaction between light and chilling temperature on the inhibition of photosynthesis in chilling‐sensitive plants*

Abstract. Fully expanded leaves of 25°C grown Phaseolus vulgaris and six other species were exposed for 3 h to chilling temperatures at photon flux densities equivalent to full sunlight. In four of the species this treatment resulted in substantial inhibition of the subsequent quantum yield of CO2 uptake, indicating reduction of the photochemical efficiency of photosynthesis. The extent of inhibition was dependent on the photon flux density during chilling and no inhibition occurred when chilling occurred at a low photon flux density. No inhibition occurred at temperatures above 11.5°C, even in the presence of the equivalent of full sunlight. This interaction between chilling and light to cause inhibition of photosynthesis was promoted by the presence of oxygen at normal air partial pressures and was unaffected by the CO2 partial pressure present when chilling occurred in air. When chilling occurred at low O2 partial pressures, CO2 was effective in reducing the degree of inhibition. Apparently, when leaves of chilling‐sensitive plants are exposed to chilling temperatures in air of normal composition then light is instrumental in inducing rapid damage to the photochemical efficiency of photosynthesis.

Inhibition of CO2 Assimilation by Supraoptimal CO2: Effect of Light and Temperature

In cotton the rate of CO2 assimilation, at O2 partial pressures up to 200 mbar, increased to a maximum and then declined as the intercellular partial pressure of CO2 was increased. The specific intercellular partial pressure of CO2 at which rate of assimilation began to decline depended on the environmental conditions. At 19 mbar partial pressure of O2 the decline occurred at CO2 partial pressure >390 �bar. At 200 mbar partial pressure of O2 it occurred at CO2 partial pressure > 534 �bar. O2 increased the CO2 partial pressure required for inhibition but it did not appear to affect the steepness of the decline of rate of assimilation with further increase in partial pressure of CO2 once the decline became apparent. The decline was more readily observed at low temperature and low O2 partial pressure, and in plants grown at low light and NO3- levels. It was also observed in cowpea and sunflower. Changes in quantum efficiency in cotton at high and low CO2 concentrations were observed. At ambient CO2 concentration (300 �bar), the quantum yields measured at 19 and 200 mbar partial pressure of O2 were 0.072 � 0.0003 and 0.053 � 0.0060 mol CO2 per mol absorbed quanta, respectively. In contrast, at 900 �bar CO2 partial pressure the respective values were 0.050 � 0.0023 and 0.070 � 0.0006 mol CO2 per mol absorbed quanta. The nature of the inhibition of CO2 assimilation by high partial pressure of CO2 is discussed.

2, 3Diphosphoglycerate (2, 3DPG) Production-degradation Systems in SHRSP and WKY

Recently, Sasaki et al. have identified DPGM with DPGP (Eur. J. Biochem. 50, 581-593, 1975). This report and our results raised a possibility that in hypertension developmental state the enzyme activities of DPGM and DPGP in erythrocytes of SHRSP showed lower levels than those of WKY. And there is another possibility that in WKY these enzyme activities may be elevated by low partial pressure of O2 in enzyme inducing process, which was not observed in SHRSP. In addition, it is supposed that in WKY erythrocytes DPGM activity may be stimulated by Hb and inhibited by HbO2, whereas DPGP activity may be inhibited by Hb and stimulated by HbO2 in erythrocytes of WKY, which was not observed in SHRSP erythrocytes.

ドロマイト系炭酸塩鉱物の熱分解

Thermal decomposition of two dolomite-like double carbonate minerals was investigated by means of DTA and X-ray technique.One was magnesian kutnahorite (Ca1.064 (Mn0.475, Mg0.437, Fe0.024)(CO3) 2) from the Ryujima mine, Nagano Prefecture, the other was ferromanganoan dolomite (Ca1.115 (Mg0.415, Fe0.225, Mn0.245)(CO3) 2) from the Budo mine, Niigata Prefecture, Japan.DTA measurements were performed in the three atmospheric conditions, 1) in static air, 2) in CO2 100ml/min gas flow, 3) in CO2 95ml/min+CO 5ml/min mixing gas flow. Their DTA curves measured in static air atmosphere using minute sample masses were quite different from those published previously. These differences might be due to the effect of self-generated atmosphere (CO2).In the CO2 gas flow at 100ml/min, the magnesian kutnahorite was decomposed in four steps, while the ferromanganoan dolomite in three steps as follows. Magnesian kutnahorite→CaCO3+Mgz MnO4+Mn304+MgO→CaCO3+CaMnO3+Mgo→CaCO3+CaMnO3+Ca2MnO4+MgO→CaMnO3+Ca2MnO4+MgO+CaO.Ferromanganoan dolomite→CaCO3+ (Fe, Mn) 3O4+MgO→CaCO3+CaMnO3+CaFe2O4+MgO→CaMnO3+CaFe2O4+MgO+CaO.However, in the flowing gas mixture of CO2 95ml/min+CO5ml/min, both samples showed two-step decomposition like dolomite according to the following processes. Magnesian kutnahorite→CaCO3+M, Mn) O→ (Ca, Mn) O+ (Mg, Mn) O. Ferromanganoan dolomite→CaCO3+ (Mg, Mn) O+Fe2O3→Ca3MgFe3O6+ (Ca, Mn) O+ (Mg, Mn) O.Consequently, it was found that a dolomite-like double carbonate could be decomposed in the two-step reaction, only when it was heated in the CO2 atmosphere having sufficiently low O2 partial pressure.

Analysis of the oxidation reactions of CaS

The chemical reactions of dense pellets of solid CaS in oxidizing atmospheres were studied by using continuous thermogravimetric analysis and iodimetric titration of SO2 in the off-gas. The experiments covered a temperature range of 1223 to 1853 K, and Ar-O2 mixtures varying from 1 to 100 pct O2. The oxidation of CaS was found to be a complex process involving the formation of CaO and CaSO4. Within the experimental conditions stated, three different processes were observed: 1) Weight loss with the formation of CaO and SO2 which occurred at high temperatures and low partial pressures of O2. 2) Weight gain which occurred at low temperatures and high partial pressures of O2. 3) Combination of a) weight gain with the overall formation of CaSO4 and b) weight loss with the overall oxidation of CaS to CaO and the decomposition of CaSO4 leading to an oscillatory behavior which occurred at intermediate temperatures and intermediate to high partial pressures of O2. The boundaries between these three processes are distinct. The rate of oxidation of the sulfide is limited first by the transport of O2 across the gas boundary layer and later by the diffusion of O2 through the porous reaction product. From these results and the Ca-S-0 stability diagram, it is possible to predict the experimental conditions which will produce processes of weight gain, weight loss and oscillatory behavior.

Effect of Light Intensity during Growth on Photoinhibition of Intact Attached Bean Leaflets

In the study reported here, two different photoinhibitory phenomena were compared within a single plant species. Bean plants were grown in three different light intensities to simulate sun and shade environments. The effects of photoinhibitory treatments on in vivo CO(2) assimilation rates and in vitro chloroplast electron transport reactions were investigated and the extent to which carbon metabolism served to prevent photoinhibition was characterized. It was shown that the photoinhibition which follows exposure of intact leaflets of low light-grown bean plants to high light intensity in normal air is essentially similar to that which occurs when leaflets of plants grown in full sunlight are illuminated in the absence of CO(2) at low O(2) partial pressures.