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O2 Consumption (o2 + consumption)
Selected AbstractsBacterial energetics, stoichiometry, and kinetic modeling of 2,4-Dinitrotoluene biodegradation in a batch respirometerENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2004Chunlong Zhang Abstract A stoichiometric equation and kinetic model were developed and validated using experimental data from batch respirometer studies on the biodegradation of 2,4-dinitrotoluene (DNT). The stoichiometric equation integrates bacterial energetics and is revised from that in a previous study by including the mass balance of phosphorus (P) in the biomass. Stoichiometric results on O2 consumption, CO2 evolution, and nitrite evolution are in good agreement with respirometer data. However, the optimal P requirement is significantly higher than the stoichiometrically derived P, implying potentially limited bioavailability of P and the need for buffering capacity in the media to mitigate the adverse pH effect for optimal growth of DNT-degrading bacteria. An array of models was evaluated to fit the O2/CO2 data acquired experimentally and the DNT depletion data calculated from derived stoichiometric coefficients and cell yield. The deterministic, integrated Monod model provides the goodness of fit to the test data on DNT depletion, and the Monod model parameters (Ks, X0, ,max, and Y) were estimated by nonlinear regression. Further analyses with an equilibrium model (MINTEQ) indicate the interrelated nature of medium chemical compositions in controlling the rate and extent of DNT biodegradation. Results from the present batch respirometer study help to unravel some key factors in controlling DNT biodegradation in complex remediation systems, in particular the interactions between acidogenic DNT bacteria and various parameters, including pH and P, the latter of which could serve as a nutrient, a buffer, and a controlling factor on the bioavailable fractions of minerals (Ca, Fe, Zn, and Mo) in the medium. [source] Effects of pre- and postnatal polychlorinated biphenyl exposure on metabolic rate and thyroid hormones of white-footed mice,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 8 2001John B. French Jr. Abstract Energy budgets have proven to be a valuable tool for predicting life history from physiological data in terrestrial vertebrates, yet these concepts have not been applied to the physiological effects of contaminants. Contaminants might affect energy budgets by imposing an additional metabolic cost or by reducing the overall amount of energy taken in; either process will reduce the energy available for production (i.e., growth or reproduction). This study examined whole animal energetic effects of polychlorinated biphenyl (PCB) exposure in white-footed mice (Peromyscus leucopus). Exposure to PCBs is known to reduce concentrations of plasma thyroid hormones, and thyroid hormones exert strong control over the rate of energy metabolism in mammals. Peromyscus leucopus that were proven breeders were fed PCBs in their food at 0, 10, and 25 ppm. Through lactation, offspring were exposed to PCB from conception and were maintained on the maternal diet to adulthood. No effects were seen on energy metabolism (O2 consumption, measured in adulthood) or on growth, but there were large dose-dependent decreases in thyroid hormone concentrations, particularly T4. The apparent disparity in our data between unchanged metabolic rates and 50% reductions in T4 concentrations can be rationalized by noting that free T3 (the fraction not bound to plasma protein) in treated mice was not significantly different from controls and that metabolism is most strongly influenced by free T3. Overall, this study did not demonstrate any energetic consequences of PCB exposure in P. leucopus at dietary concentrations up to 25 ppm. [source] Estimating diesel degradation rates from N2, O2 and CO2 concentration versus depth data in a loamy sandEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2007J. Van De Steene Summary The degradation rate of the pollutant is often an important parameter for designing and maintaining an active treatment system or for determining the rate of natural attenuation. A quasi-steady-state gas transport model based on Fick's law with a correction term for advective flux, for estimating diesel degradation rates from N2, O2 and CO2 concentration versus depth data, was evaluated in a laboratory column study. A loamy sand was spiked with diesel fuel at 0, 1000, 5000 and 10 000 mg kg,1 soil (dry weight basis) and incubated for 15 weeks. Soil gas was sampled weekly at 6 selected depths in the columns and analysed for O2, CO2 and N2 concentrations. The agreement between the measured and the modelled concentrations was good for the untreated soil (R2= 0.60) and very good for the soil spiked with 1000 mg kg,1 (R2= 0.96) and 5000 mg kg,1 (R2= 0.97). Oxygen consumption ranged from ,0.15 to ,2.25 mol O2 m,3 soil day,1 and CO2 production ranged from 0.20 to 2.07 mol CO2 m,3 soil day,1. A significantly greater mean O2 consumption (P < 0.001) and CO2 production (P < 0.005) over time was observed for the soils spiked with diesel compared with the untreated soil, which suggests biodegradation of the diesel substrate. Diesel degradation rates calculated from respiration data were 1.5,2.1 times less than the change in total petroleum hydrocarbon content. The inability of this study to correlate respiration data to actual changes in diesel concentration could be explained by volatilization, long-term sorption of diesel hydrocarbons to organic matter and incorporation of diesel hydrocarbons into microbial biomass, aspects of which require further investigation. [source] Nitric oxide synthase inhibition reduces O2 cost of force development and spares high-energy phosphates following contractions in pump-perfused rat hindlimb musclesEXPERIMENTAL PHYSIOLOGY, Issue 3 2006David J. Baker The purpose of the present experiments was to test the hypotheses that: (i) nitric oxide synthase (NOS) inhibition reduces the O2 cost of force development across a range of contractile demands; and (ii) this reduced O2 cost of force development would be reflected in a sparing of intramuscular higher energy phosphates. Rat distal hindlimb muscles were pump perfused in situ and electrically stimulated (200 ms trains with pulses at 100 Hz, each pulse 0.05 ms duration) for 1 min each at 15, 30 and 60 tetani min,1 and for 2 min at 90 tetani min,1 in three groups: 0.01 mm adenosine; 1 mm d -NAME and 0.01 mm adenosine (d -NAME); and 1 mm l -NAME and 0.01 mm adenosine (l -NAME). The gastrocnemius,plantaris,soleus muscle group was freeze clamped post-contractions for metabolite analyses. Force was 19% higher and oxygen uptake was 20% lower with l -NAME versus adenosine, and there was a 35% reduction in /time-integrated tension versus adenosine and 24% versusd -NAME that was independent of contraction frequency. l -NAME treatment produced a 33% sparing of muscle phosphocreatine (PCr), and intramuscular lactate was no different between groups. In contrast, d -NAME reduced force by 30%, by 29% and the O2 cost of force development by 15% compared with adenosine, but had no effect on the degree of intramuscular ATP and PCr depletion. These results show that NOS inhibition improved the metabolic efficiency of force development, either by improving the ATP yield for a given O2 consumption or by reducing the ATP cost of force development. In addition, these effects were independent of contraction frequency. [source] dye (arc) mutants: insights into an unexplained phenotype and its suppression by the synthesis of poly (3-hydroxybutyrate) in Escherichia coli recombinantsFEMS MICROBIOLOGY LETTERS, Issue 1 2006Jimena A. Ruiz Abstract arcA codes for a central regulator in Escherichia coli that responds to redox conditions of growth. Mutations in this gene, originally named dye, confer sensitivity to toluidine blue and other redox dyes. However, the molecular basis for the dye-sensitive phenotype has not been elucidated. In this work, we show that toluidine blue redirects electrons to O2 and causes an increase in the generation of reactive O2 species (ROS). We also demonstrate that synthesis of poly (3-hydroxybutyrate) suppresses the Dye phenotype in E. coli recombinants, as the capacity to synthesize the polymer reduces sensitivity to toluidine blue, O2 consumption and ROS production levels. [source] Respiratory protection of nitrogenase in Azotobacter species: is a widely held hypothesis unequivocally supported by experimental evidence?FEMS MICROBIOLOGY REVIEWS, Issue 4 2000Jürgen Oelze Abstract The hypothesis of respiratory protection, originally formulated on the basis of results obtained with Azotobacter species, postulates that consumption of O2 at the surface of diazotrophic prokaryotes protects nitrogenase from inactivation by O2. Accordingly, it is assumed that, at increased ambient O2 concentrations, nitrogenase activity depends on increased activities of a largely uncoupled respiratory electron transport system. The present review compiles evidence indicating that cellular O2 consumption as well as both the activity and the formation of the respiratory system of Azotobacter vinelandii are controlled by the C/N ratio, that is to say the ratio at which the organism consumes the substrate (i.e. the source of carbon, reducing equivalents and ATP) per source of compound nitrogen. The maximal respiratory capacity which can be attained at increased C/N ratios, however, is controlled, within limits, by the ambient O2 concentration. When growth becomes N-limited at increased C/N ratios, cells synthesize nitrogenase and fix N2. Under these diazotrophic conditions, cellular O2 consumption remains constant at a level controlled by the O2 concentration. Control by O2 has been studied on the basis of both whole cell respiration and defined segments of the respiratory electron transport chain. The results demonstrate that the effect of O2 on the respiratory system is restricted to the lower range of O2 concentrations up to about 70 ,M. Nevertheless, azotobacters are able to grow diazotrophically at dissolved O2 concentrations of up to about 230 ,M indicating that respiratory protection is not warranted at increased ambient O2 concentrations. This conclusion is supported and extended by a number of results largely excluding an obvious relationship between nitrogenase activity and the actual rate of cellular O2 consumption. On the basis of theoretical calculations, it is assumed that the rate of O2 diffusion into the cells is not significantly affected by respiration. All of these results lead to the conclusion that, in the protection of nitrogenase from O2 damage, O2 consumption at the cell surface is less effective than generally assumed. It is proposed that alternative factors like the supply of ATP and reducing equivalents are more important. [source] The product of the gene GEF1 of Saccharomyces cerevisiae transports Cl, across the plasma membraneFEMS YEAST RESEARCH, Issue 8 2007Angélica López-Rodríguez Abstract Expression of GEF1 in Xenopus laevis oocytes and HEK-293 cells gave rise to a Cl, channel that remained permanently open and was blocked by nitro-2-(3-phenylpropylamino) benzoic acid and niflumic acid. NPPB induced petite -like colonies, resembling the GEF1 knock-out. The fluorescent halide indicator SPQ was quenched in a wild-type strain, in contrast to both a GEF1 knock-out strain and yeast grown in the presence of NPPB. Immunogold and electron microscopy located Gef1p in the plasma membrane, vacuole, endoplasmic reticulum and Golgi apparatus. Eleven substitutions in five residues forming the ion channel of GEF1 were introduced; some of them (S186A, I188N, Y459D, Y459F, Y459V, I467A, I467N and F468N) did not rescue the pet phenotype, whereas F468A, A558F and A558Y formed normal colonies. All the pet mutants showed reduced O2 consumption, small mitochondria and mostly disrupted organelles. Finally, electron microscopy revealed that the plasma membrane of the mutants develop multiple foldings and highly ordered cylindrical protein-membrane complexes. All the experiments above suggest that Gef1p transports Cl, through the plasma membrane and reveal the importance of critical amino acids for the proper function of the protein as suggested by structural models. However, the mechanism of activation of the channel has yet to be defined. [source] Benthic microbial respiration in Appalachian Mountain, Piedmont, and Coastal Plains streams of the eastern U.S.A.FRESHWATER BIOLOGY, Issue 2 2002B. H. Hill 1.,Benthic microbial respiration was measured in 214 streams in the Appalachian Mountain, Piedmont, and Coastal Plains regions of the eastern United States in summer 1997 and 1998. 2.,Respiration was measured as both O2 consumption in sealed microcosms and as dehydrogenase activity (DHA) of the sediments contained within the microcosms. 3.,Benthic microbial respiration in streams of the eastern U.S., as O2 consumption, was 0.37 ± 0.03 mg O2 m,2 day,1. Respiration as DHA averaged 1.21 ± 0.08 mg O2 m,2 day,1 4.,No significant differences in O2 consumption or DHA were found among geographical provinces or stream size classes, nor among catchment basins for O2 consumption, but DHA was significantly higher in the other Atlantic (non-Chesapeake Bay) catchment basins. 5.,Canonical correlation analyses generated two environmental axes. The stronger canonical axis (W1) represented a chemical disturbance gradient that was negatively correlated with signatures of anthropogenic impacts (ANC, Cl,, pH, SO42), and positively correlated with riparian canopy cover and stream water dissolved organic carbon concentration (DOC). A weaker canonical axis (W2) was postively correlated with pH, riparian zone agriculture, and stream depth, and negatively correlated with DOC and elevation of the stream. Oxygen consumption was significantly correlated with W2 whereas DHA was significantly correlated with W1. 6.,The strengths of the correlations of DHA with environmental variables, particularly those that are proven indicators of catchment disturbances and with the canonical axis, suggest that DHA is a more responsive measure of benthic microbial activity than is O2 consumption. [source] Avian seasonal metabolic variation in a subtropical desert: basal metabolic rates are lower in winter than in summerFUNCTIONAL ECOLOGY, Issue 2 2010Ben Smit Summary 1Most small birds inhabiting temperate latitudes in the Holarctic increase basal metabolic rate (BMR) in winter, a pattern thought to reflect the up-regulation of metabolic machinery required for enhanced winter cold tolerance. In contrast, patterns of seasonal BMR variation in birds inhabiting subtropical latitudes are largely unknown. In this study, we investigate seasonal BMR changes in species from subtropical latitudes, and analyse global variation in the direction and magnitude of these responses. 2We estimated winter and summer BMR in five species resident in the Kalahari Desert, using flow-through respirometry to measure O2 consumption and CO2 production in birds held overnight in a field laboratory. 3In all five species, mass-specific BMR was significantly lower in winter than in summer, with mean reductions of 23% in African scops-owls (Otus senegalensis), 30% in pearl-spotted owlets (Glaucidium perlatum), 35% in fork-tailed drongos (Dicrurus adsimilis), 29% in crimson-breasted shrikes (Laniarius atrococcinneus), and 17% in white-browed sparrow-weavers (Plocepasser mahali). 4An analysis of global variation in seasonal BMR changes reveals that their magnitude and direction vary with latitude, ranging from pronounced winter increases at high latitudes where winters are extremely cold, to the opposite pattern in warmer, subtropical environments. 5Our empirical results for five species, taken together with the analysis of global variation, are consistent with the hypothesis that winter metabolism in subtropical environments is driven primarily by the need for energy and/or water conservation rather than cold tolerance. [source] Cardiovascular and Metabolic Effects of High-dose Insulin in a Porcine Septic Shock ModelACADEMIC EMERGENCY MEDICINE, Issue 4 2010Joel S. Holger MD Abstract Objectives:, High-dose insulin (HDI) has inotropic and vasodilatory properties in various clinical conditions associated with myocardial depression. The authors hypothesized that HDI will improve the myocardial depression produced by severe septic shock and have beneficial effects on metabolic parameters. In an animal model of severe septic shock, this study compared the effects of HDI treatment to normal saline (NS) resuscitation alone. Methods:, Ten pigs were randomized to an insulin (HDI) or NS group. All were anesthetized and instrumented to monitor cardiovascular function. In both arms, Escherichia coli endotoxin lipopolysaccharide (LPS) and NS infusions were begun. LPS was titrated to 20 ,g/kg/hour over 30 minutes and continued for 5 hours, and saline was infused at 20 mL/kg/hour throughout the protocol. Dextrose (50%) was infused to maintain glucose in the 60,150 mg/dL range, and potassium was infused to maintain a level greater than 2.8 mmol/L. At 60 minutes, the HDI group received an insulin infusion titrated from 2 to 10 units/kg/hour over 40 minutes and continued at that rate throughout the protocol. Survival, heart rate (HR), mean arterial pressure (MAP), pulmonary artery and central venous pressure, cardiac output, central venous oxygen saturation (SVO2), and lactate were monitored for 5 hours (three pigs each arm) or 7 hours (two pigs each arm) or until death. Cardiac index, systemic vascular resistance (SVR), pulmonary vascular resistance (PVR), O2 delivery, and O2 consumption were derived from measured data. Outcomes from the repeated-measures analysis were modeled using a mixed-effects linear model that assumed normally distributed errors and a random effect at the subject level. Results:, No significant baseline differences existed between arms at time 0 or 60 minutes. Survival was 100% in the HDI arm and 60% in the NS arm. Cardiovascular variables were significantly better in the HDI arm: cardiac index (p < 0.001), SVR (p < 0.003), and PVR (p < 0.01). The metabolic parameters were also significantly better in the HDI arm: SVO2 (p < 0.01), O2 delivery (p < 0.001), and O2 consumption (p < 0.001). No differences in MAP, HR, or lactate were found. Conclusions:, In this animal model of endotoxemic-induced septic shock that results in severe myocardial depression, HDI is associated with improved cardiac function compared to NS resuscitation alone. HDI also demonstrated favorable metabolic, pulmonary, and peripheral vascular effects. Further studies may define a potential role for the use of HDI in the resuscitation of septic shock. ACADEMIC EMERGENCY MEDICINE 2010; 17:429,435 © 2010 by the Society for Academic Emergency Medicine [source] Prostate carcinoma cells selected by long-term exposure to reduced oxygen tension show remarkable biochemical plasticity via modulation of superoxide, HIF-1, levels, and energy metabolismJOURNAL OF CELLULAR PHYSIOLOGY, Issue 3 2007Jeanne Bourdeau-Heller Cancer cells are able to tolerate levels of O2 that are damaging or lethal to normal cells; we hypothesize that this tolerance is the result of biochemical plasticity which maintains cellular homeostasis of both energy levels and oxidation state. In order to examine this hypothesis, we used different O2 levels as a selective agent during long-term culture of DU145 prostate cancer cells to develop three isogenic cell lines that grow in normoxic (4%), hyperoxic (21%), or hypoxic (1%) O2 conditions. Growth characteristics and O2 consumption differed significantly between these cell lines without changes in ATP levels or altered sensitivity to 2-deoxy- D -glucose, an inhibitor of glycolysis. O2 consumption was significantly higher in the hyperoxic line as was the level of endogenous superoxide. The hypoxic cell line regulated the chemical gradient of the proton motive force (PMF) independent of the electrical component without O2 -dependent changes in Hif-1, levels. In contrast, the normoxic line regulated Hif-1, without tight regulation of the chemical component of the PMF noted in the hypoxic cell line. From these studies, we conclude that selection of prostate cancer cells by long-term exposure to low ambient levels of O2 resulted in cells with unique biochemical properties in which energy metabolism, reactive oxygen species (ROS), and HIF-1, levels are modulated to allow cell survival and growth. Thus, cancer cells exhibit remarkable biochemical plasticity in response to various O2 levels. J. Cell. Physiol. 212:744,752, 2007. © 2007 Wiley-Liss, Inc. [source] Respiration of steelhead trout sperm: sensitivity to pH and carbon dioxideJOURNAL OF FISH BIOLOGY, Issue 1 2003R. L. Ingermann Steelhead trout Oncorhynchus mykiss sperm held in seminal plasma or sperm-immobilizing buffer (pH 8·6) at 10° C consumed O2 at the rate of c. 2 nmol O2 min,1 10,9 sperm; the rate of O2 consumption was not different in sperm held for 4 or 24 h. Decreasing the extracellular pH from 8·5 to 7·5 either by diluting semen with buffer titrated with HCl or by increasing the partial pressure of CO2 in the incubation atmosphere resulted in c. a 40% decrease in the rate of sperm respiration. The data did not, however, support the hypothesis that the precipitous reduction in the capacity for sperm motility that occurs as external pH is reduced is a result of a decrease in cellular metabolism. The rate of O2 consumption of freshly collected semen from different males was not correlated to cellular ATP content or to the proportion of sperm that were motile upon activation; the initial ATP content and sperm motility were positively correlated. The rate of O2 consumption was not significantly increased following sperm activation or by the addition of an uncoupler of oxidative phosphorylation, carbonyl cyanide p -trifluoromethoxyphenylhydrazone, suggesting that these sperm have little, if any, capacity for increased oxidative metabolism. [source] Browning Prevention by Ascorbic Acid and 4-Hexylresorcinol: Different Mechanisms of Action on Polyphenol Oxidase in the Presence and in the Absence of SubstratesJOURNAL OF FOOD SCIENCE, Issue 9 2007E. Arias ABSTRACT:, We have investigated the mechanism of action of 4-hexylresorcinol (4-HR) and ascorbic acid (AA) on the polyphenol oxidase (PPO) catalyzed oxidation of phenolic substrates. Incubation of PPO with 4-HR diminishes strongly PPO activity. This effect can be erroneously interpreted, due to the high affinity of 4-HR for PPO, as irreversible inactivation of PPO. However, PPO activity can be recovered by dialysis after incubation with 4-HR. 4-hexylresorcinol is a canonical enzyme inhibitor that binds preferentially to the oxy form of PPO. It is a mixed-type inhibitor, because it influences both apparent Vmax (1.26 compared with 0.4 units in the absence and presence of 4-HR, respectively) and Km values (0.28 mM compared with 0.97 mM in the absence and in the presence of 4-HR, respectively) of PPO. AA can prevent browning by 2 different mechanisms: In the absence of PPO substrates it inactivates PPO irreversibly, probably through binding to its active site, preferentially in its oxy form. In the presence of PPO substrates, AA reduces PPO oxidized reaction products, which results in a lag phase when measuring PPO activity by monitoring dark product formation but not when monitoring O2 consumption. The simultaneous use of both 4-HR and AA on PPO results in additive prevention of browning. [source] Light-dependent oxygen consumption in nitrogen-fixing cyanobacteria plays a key role in nitrogenase protection,JOURNAL OF PHYCOLOGY, Issue 5 2007Allen J. Milligan All colonial diazotrophic cyanobacteria are capable of simultaneously evolving O2 through oxygenic photosynthesis and fixing nitrogen via nitrogenase. Since nitrogenase is irreversibly inactivated by O2, accommodation of the two metabolic pathways has led to biochemical and/or structural adaptations that protect the enzyme from O2. In some species, differentiated cells (heterocysts) are produced within the filaments. PSII is absent in the heterocysts, while PSI activity is maintained. In other, nonheterocystous species, however, a "division of labor" occurs whereby individual cells within a colony appear to ephemerally fix nitrogen while others evolve oxygen. Using membrane inlet mass spectrometry (MIMS) in conjunction with tracer 18O2 and inhibitors of photosynthetic and respiratory electron transport, we examined the light dependence of O2 consumption in Trichodesmium sp. IMS 101, a nonheterocystous, colonial cyanobacterium, and Anabaena flos-aquae (Lyngb.) Bréb. ex Bornet et Flahault, a heterocystous species. Our results indicate that in both species, intracellular O2 concentrations are maintained at low levels by the light-dependent reduction of oxygen via the Mehler reaction. In N2 -fixing Trichodesmium colonies, Mehler activity can consume ,75% of gross O2 production, while in Trichodesmium utilizing nitrate, Mehler activity declines and consumes ,10% of gross O2 production. Moreover, evidence for the coupling between N2 fixation and Mehler activity was observed in purified heterocysts of Anabaena, where light accelerated O2 consumption by 3-fold. Our results suggest that a major role for PSI in N2 -fixing cyanobacteria is to effectively act as a photon-catalyzed oxidase, consuming O2 through pseudocyclic electron transport while simultaneously supplying ATP in both heterocystous and nonheterocystous taxa. [source] Effect of Salt Stress on Carbon Metabolism and Bacteroid Respiration in Root Nodules of Common Bean (Phaseolus vulgaris L.)PLANT BIOLOGY, Issue 4 2000A. Ferri Abstract: In the present work, we examined the effect of salinity on growth, N fixation and carbon metabolism in the nodule cytosol and bacteroids of Phaseolus vulgaris, and measured the O2 consumption by bacteroids incubated with or without the addition of exogenous respiratory substrates. The aim was to ascertain whether the compounds that accumulate under salt stress can increase bacteroid respiration and whether this capacity changes in response to salinity in root nodules of Phaseolus vulgaris. The plants were grown in a controlled environment chamber, and 50, 100 mM or no NaCl (control) was added to the nutrient solution. Two harvests were made, at the vegetative growth period and at the beginning of the reproductive period. The enzyme activities in the nodule cytosol were reduced by the salt treatments, while in the bacteroid cytosol the enzyme activities increased at high salt concentrations at the first harvest and for ADH in all treatments. The data presented here confirm that succinate and malate are the preferred substrates for bacteroid respiration in common bean, but these bacteroids may also utilize glucose, either in control or under saline conditions. The addition of proline or lactate to the incubation medium significantly raised oxygen consumption in the bacteroids isolated from plants treated with salt. [source] Xylem sap flow as a major pathway for oxygen supply to the sapwood of birch (Betula pubescens Ehr.)PLANT CELL & ENVIRONMENT, Issue 11 2003D. GANSERT ABSTRACT The role of xylem sap flow as an aqueous pathway for oxygen supply to the wood parenchyma of Betula pubescens saplings was investigated. Using micro-optode sensors the oxygen status of the sapwood was quantified in relation to mass flow of xylem sap. Sap flow was gradually reduced by an increasing oxygen depletion in the root space. The effect of sap flow on radial O2 transport between stem and atmosphere was assessed by a stoichiometrical approach between respiratory CO2 production and O2 consumption. Restriction of sap flow set in 36.5 h after the onset of O2 depletion, and was complete after 71 h. Interruption of sap flow drastically increased the O2 deficit in the sapwood to 70%. Sap flow contributed about 60% to the total oxygen supply to the sapwood. Diurnal O2 flow rates varied between 3 and 6.3 nmol O2 m,2 leaf area (LA) s,1 during night- and daytime, respectively. Maximum O2 flow rates of 20 nmol O2 m,2 LA s,1 were reached at highest sap flow rates of 5.7 mmol H2O m,2 LA s,1. Sap flow not only affected the oxygen status of the sapwood but also had an effect on radial O2 transport between stem and atmosphere. [source] Regulation of lactate production at the onset of ischaemia is independent of mitochondrial NADH/NAD+: insights from in silico studiesTHE JOURNAL OF PHYSIOLOGY, Issue 3 2005Lufang Zhou Ischaemia decreases mitochondrial NADH oxidation, activates glycolysis, increases the NADH/NAD+ ratio, and causes lactate production. The mechanisms that regulate anaerobic glycolysis and the NADH/NAD+ ratio during ischaemia are unclear. Although continuous measurements of metabolic fluxes and NADH/NAD+ in cytosol and mitochondria are not possible in vivo with current experimental techniques, computational models can be used to predict these variables by simulations with in silico experiments. Such predictions were obtained using a mathematical model of cellular metabolism in perfused myocardium. This model, which distinguishes cytosolic and mitochondrial domains, incorporates key metabolic species and processes associated with energy transfer. Simulation of metabolic responses to mild, moderate and severe ischaemia in large animals showed that mitochondrial NADH/NAD+ was rapidly reset to higher values in proportion to the reduced O2 delivery and myocardial oxygen consumption . Cytosolic NADH/NAD+, however, showed a biphasic response, with a sharp initial increase that was due to activation of glycogen breakdown and glycolysis, and corresponded with lactate production. Whereas the rate of glycolysis and the malate,aspartate shuttle had a significant effect on the cytosolic NADH/NAD+, their effects on the mitochondrial NADH/NAD+ were minimal. In summary, model simulations of the metabolic response to ischaemia showed that mitochondrial NADH/NAD+ is primarily determined by O2 consumption, while cytosolic NADH/NAD+ is largely a function of glycolytic flux during the initial phase, and is determined by mitochondrial NADH/NAD+ and the malate,aspartate shuttle during the steady state. [source] Recurrent spreading depolarizations after subarachnoid hemorrhage decreases oxygen availability in human cerebral cortexANNALS OF NEUROLOGY, Issue 5 2010Bert Bosche MD Objective Delayed ischemic neurological deficit (DIND) contributes to poor outcome in subarachnoid hemorrhage (SAH) patients. Because there is continuing uncertainty as to whether proximal cerebral artery vasospasm is the only cause of DIND, other processes should be considered. A potential candidate is cortical spreading depolarization (CSD)-induced hypoxia. We hypothesized that recurrent CSDs influence cortical oxygen availability. Methods Centers in the Cooperative Study of Brain Injury Depolarizations (COSBID) recruited 9 patients with severe SAH, who underwent open neurosurgery. We used simultaneous, colocalized recordings of electrocorticography and tissue oxygen pressure (ptiO2) in human cerebral cortex. We screened for delayed cortical infarcts by using sequential brain imaging and investigated cerebral vasospasm by angiography or time-of-flight magnetic resonance imaging. Results In a total recording time of 850 hours, 120 CSDs were found in 8 of 9 patients. Fifty-five CSDs (,46%) were found in only 2 of 9 patients, who later developed DIND. Eighty-nine (,75%) of all CSDs occurred between the 5th and 7th day after SAH, and 96 (80%) arose within temporal clusters of recurrent CSD. Clusters of CSD occurred simultaneously, with mainly biphasic CSD-associated ptiO2 responses comprising a primary hypoxic and a secondary hyperoxic phase. The frequency of CSD correlated positively with the duration of the hypoxic phase and negatively with that of the hyperoxic phase. Hypoxic phases significantly increased stepwise within CSD clusters; particularly in DIND patients, biphasic ptiO2 responses changed to monophasic ptiO2 decreases within these clusters. Monophasic hypoxic ptiO2 responses to CSD were found predominantly in DIND patients. Interpretation We attribute these clinical ptiO2 findings mainly to changes in local blood flow in the cortical microcirculation but also to augmented metabolism. Besides classical contributors like proximal cerebral vasospasm, CSD clusters may reduce O2 supply and increase O2 consumption, and thereby promote DIND. ANN NEUROL 2010;67:607,617 [source] Energy budget of the Japanese flounder Paralichthys olivaceus (Temminck & Schlegel) larvae fed HUFA-enriched and non-enriched Artemia naupliiAQUACULTURE RESEARCH, Issue 10 2003O Sumule Abstract The energy budget of the Japanese flounder Paralichthys olivaceus (Temminck & Schlegel) larvae fed enriched (EA) and non-enriched (NEA) Artemia nauplii was determined by equating energy intake (EI) with the summation of energy channelled to faeces (F), metabolism (M), excretion (U) and growth (G). Larvae (21 days post hatching, 2.2 mg mean wet wt) were reared in six 80-L circular tanks with three replicates of 160 larvae per tank and fed EA and NEA for 20 days. EI was calculated from the energy content of consumed nauplii, M from the summation of energy for routine, feeding and active metabolisms, U from ammonia excretion and G from energy gained based on weight gain, while F was the difference between EI and the total of other components. The heat increment of larvae was calculated from the difference of O2 consumption at post-prandial and routine conditions. Except for G and F, variables were correlated to the dry body weight (W) of larvae in a power function: Y=aWb. Coefficients a and b were estimated by regression after a logarithmic transformation of the raw data. Overall, growth and survival rates of the larvae fed EA were higher than those fed NEA. For a larval flounder growing from 2 to 20 mg wet wt, the ingested energy was partitioned as follows: 22.8% to faecal loss, 38.3% to metabolism, 1.5% to urinary loss and 37.4% to growth for the EA group, whereas 35.4% to faecal loss, 28.4% to metabolism, 1.3% to urinary loss and 34.9% to growth for the NEA group. Gross conversion and assimilation efficiencies were higher, but the net conversion efficiency was lower in EA-fed larvae than NEA-fed larvae. This study suggests that the higher growth and survival rates of the EA-fed group compared with the NEA-fed group were attributed to their higher intake of essential fatty acids, higher metabolism and lower energy loss of faeces. [source] 2412: Laser and oxygenACTA OPHTHALMOLOGICA, Issue 2010CJ POURNARAS Purpose To evaluate the changes in the retinal oxygen partial pressure (PO2) following photocoagulation as well as the resulting effect of the laser induced improved oxygenation, on the retinal vessels hemodynamics. Methods Measurements of the partial pressure of oxygen (PO2) distribution within the retina in various animal species using oxygen sensitive microelectrodes and evaluation of changes on the retinal vessels reactivity, following laser treatment, gave additional insights concerning photocoagulation mechanisms. Results Preretinal intervascular PO2 , far away from vessels, remain constant in all retinal areas. Intervascular intraretinal PO2 gradually decreases from both the vitreo-retinal interface and the choroid towards the mid-retina. Close to the pigment epithelium, it is significantly higher than at the vitreoretinal interface due to the much higher O2 supply provided by choroidal compaires to retinal circulation. Laser photocoagulation reduces the outer retina O2 consumption and allows O2 diffusion into the inner retina from the choroid raising the PO2 in the inner healthy retinal layers and in the preretinal intervascular normal areas. In this way, laser treatment relieves retinal hypoxia in experimental branch vein occlusion (BRVO). In patients with diabetic retinopathy (DR), the retinal PO2 is also higher in areas previously treated with laser. Following photocoagulation, the resulting reversal of hypoxia, the down-regulation of the VEGF expression, the retinal vasculature constriction and the improvement of the auto-regulatory response to physiological stimuli, all affect favorably both the retinal neovascularisation and macular edema. Conclusion Photocoagulation induces an increase of the inner retinal oxygenation resulting to an improvement of the autoregulatory retinal vessels response. [source] Retinal photocoagulation and oxygenationACTA OPHTHALMOLOGICA, Issue 2009CJ POURNARAS Purpose The clinical role of photocoagulation for the treatment of hypoxia related complications of retinal ischemic microangiopathies is well established. Methods Measurements of the partial pressure of oxygen (PO2) distribution within the the retina in various animal species using oxygen sensitive microelectrodes and evaluation of the retinal vessels reactivity by laser doppler velocimetry gave additional insights concerning photocoagulation mechanisms. Results The PO2 within the vitreo-retinal interface is heterogeneous. Preretinal and trans-retinal PO2 profiles indicate that the preretinal PO2 far away from vessels remain constant in all retinal areas. Intervascular intraretinal PO2 gradually decreases from both the vitreo-retinal interface and the choroid towards the mid-retina. Close to the pigment epithelium, it is significantly higher than at the vitreoretinal interface due to the much higher O2 supply provided by choroidal compaires to retinal circulation. Laser photocoagulation reduces the outer retina O2 consumption and allows O2 diffusion into the inner retina from the choroid raising the PO2 in the inner healthy retinal layers and in the preretinal intervascular normal areas. In this way laser treatment relieves retinal hypoxia in experimental branch vein occlusion (BRVO). In patients with diabetic retinopathy (DR), the retinal PO2 is higher in areas previously treated with laser. Following photocoagulation, the resulting reversal of hypoxia, the retinal vasculature constriction and the improvement of the regulatory response to hyperoxia all affect favorably both the retinal neovascularisation and macular edema. Conclusion Photocoagulation induces an increase of the inner retinal oxygenation reversing the retinal hypoxia and improving the regulatory response of the retinal vessels [source] RENAL OXYGEN DELIVERY: MATCHING DELIVERY TO METABOLIC DEMANDCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 10 2006Paul M O'Connor SUMMARY 1The kidneys are second only to the heart in terms of O2 consumption; however, relative to other organs, the kidneys receive a very high blood flow and oxygen extraction in the healthy kidney is low. Despite low arterial,venous O2 extraction, the kidneys are particularly susceptible to hypoxic injury and much interest surrounds the role of renal hypoxia in the development and progression of both acute and chronic renal disease. 2Numerous regulatory mechanisms have been identified that act to maintain renal parenchymal oxygenation within homeostatic limits in the in vivo kidney. However, the processes by which many of these mechanisms act to modulate renal oxygenation and the factors that influence these processes remain poorly understood. 3A number of such mechanisms specific to the kidney are reviewed herein, including the relationship between renal blood flow and O2 consumption, pre- and post-glomerular arterial,venous O2 shunting, tubulovascular cross-talk, the differential control of regional kidney blood flow and the tubuloglomerular feedback mechanism. 4The roles of these mechanisms in the control of renal oxygenation, as well as how dysfunction of these mechanisms may lead to renal hypoxia, are discussed. [source] Hypervolaemia improves global and local function and efficiency in postischaemic myocardiumCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 8 2001FY Du SUMMARY 1. In the present study, we investigated the effects of blood volume on postischaemic function and efficiency. In 14 anaesthetized dogs, following recovery from a period of 15 min occlusion of the left anterior descending coronary artery, the effects of hypervolaemia (HYPER; 15% increased volume produced by fast infusion of Hespan; B Braun Medical, Irvine, CA, USA), normovolaemia (NORMO) and hypovolaemia (HYPO) were studied. 2. Although myocardial O2 consumption was not significantly increased by volume (6.37±0.94 vs 6.89±1.1 mL/min per 100 g for HYPO and HYPER, respectively), local work of the stunned myocardium was markedly elevated (8.8±1.7 vs 22.5±3.5 g·mm/ beat, for HYPO and HYPER, respectively; P < 0.05). External work of the heart was also significantly improved (71.8±12.7 vs 139.5±16.2 mmHg·L/min for HYPO and HYPER, respectively). These data indicate markedly improved efficiency produced by volume, because work was increased with no change in myocardial O2 consumption. 3. Local dysfunction was characterized by several parameters, including systolic bulge, end-diastolic length, delay to onset of shortening, end shortening time delay (EST) and tail work ratio. Hypervolaemia reduced EST compared with hypovolaemia (98.6±18.3 vs 110.7±14.9 msec, respectively; P < 0.05) and improved tail work ratio (28.0±7.0 vs 36.0±7.0%, respectively; P < 0.05), with no effects on systolic bulge, end-diastolic length and delay to onset of shortening. 4. Thus, even in the postischaemic myocardium, increasing work by volume is energetically efficient and is accompanied by partial improvement of local dysfunction. [source] Intensity of Nordic Walking in young females with different peak O2 consumptionCLINICAL PHYSIOLOGY AND FUNCTIONAL IMAGING, Issue 5 2009Toivo Jürimäe Summary The purpose of this cross - sectional study was to determine the physiological reaction to the different intensity Nordic Walking exercise in young females with different aerobic capacity values. Twenty-eight 19,24-year-old female university students participated in the study. Their peak O2 consumption (VO2 peak kg,1) and individual ventilatory threshold (IVT) were measured using a continuous incremental protocol until volitional exhaustion on treadmill. The subjects were analysed as a whole group (n = 28) and were also divided into three groups based on the measured VO2 peak kg,1 (Difference between groups is 1 SD) as follows: 1. >46 ml min,1 kg,1 (n = 8), 2. 41,46 ml min,1 kg,1 (n = 12) and 3. <41 ml min,1 kg,1 (n = 8). The second test consisted of four times 1 km Nordic Walking with increasing speed on the 200 m indoor track, performed as a continuous study (Step 1 , slow walking, Step 2 , usual speed walking, Step 3 , faster speed walking and Step 4 , maximal speed walking). During the walking test expired gas was sampled breath-by-breath and heart rate (HR) was recorded continuously. Ratings of perceived exertion (RPE) were asked using the Borg RPE scale separately for every 1 km of the walking test. No significant differences emerged between groups in HR of IVT (172·4 ± 10·3,176·4 ± 4·9 beats min,1) or maximal HR (190·1 ± 7·3,191·6 ± 7·8 beats min,1) during the treadmill test. During maximal speed walking the speed (7·4 ± 0·4,7·5 ± 0·6 km h,1) and O2 consumption (30·4 ± 3·9,34·0 ± 4·5 ml min,1 kg,1) were relatively similar between groups (P > 0·05). However, during maximal speed walking, the O2 consumption in the second and third groups was similar with the IVT (94·9 ± 17·5% and 99·4 ± 15·5%, respectively) but in the first group it was only 75·5 ± 8·0% from IVT. Mean HR during the maximal speed walking was in the first group 151·6 ± 12·5 beats min,1, in the second (169·7 ± 10·3 beats min,1) and the third (173·1 ± 15·8 beats min,1) groups it was comparable with the calculated IVT level. The Borg RPE was very low in every group (11·9 ± 2·0,14·4 ± 2·3) and the relationship with VO2and HR was not significant during maximal speed Nordic Walking. In summary, the present study indicated that walking is an acceptable exercise for young females independent of their initial VO2 peak level. However, females with low initial VO2 peak can be recommended to exercise with the subjective ,faster speed walking'. In contrast, females with high initial VO2 peak should exercise with maximal speed. [source] | ||||||||||||||||||||||||||||