Measured O2 Consumption Research Articles

Relationship between oxygen consumption and neuronal activity in a defined neural circuit

BackgroundNeuronal computations related to sensory and motor activity along with the maintenance of spike discharge, synaptic transmission, and associated housekeeping are energetically demanding. The most efficient metabolic process to provide large amounts of energy equivalents is oxidative phosphorylation and thus dependent on O2 consumption. Therefore, O2 levels in the brain are a critical parameter that influences neuronal function. Measurements of O2 consumption have been used to estimate the cost of neuronal activity; however, exploring these metabolic relationships in vivo and under defined experimental conditions has been limited by technical challenges.ResultsWe used isolated preparations of Xenopus laevis tadpoles to perform a quantitative analysis of O2 levels in the brain under in vivo-like conditions. We measured O2 concentrations in the hindbrain in relation to the spike discharge of the superior oblique eye muscle-innervating trochlear nerve as proxy for central nervous activity. In air-saturated bath Ringer solution, O2 levels in the fourth ventricle and adjacent, functionally intact hindbrain were close to zero. Inhibition of mitochondrial activity with potassium cyanide or fixation of the tissue with ethanol raised the ventricular O2 concentration to bath levels, indicating that the brain tissue consumed the available O2. Gradually increasing oxygenation of the Ringer solution caused a concurrent increase of ventricular O2 concentrations. Blocking spike discharge with the local anesthetics tricaine methanesulfonate diminished the O2 consumption by ~ 50%, illustrating the substantial O2 amount related to neuronal activity. In contrast, episodes of spontaneous trochlear nerve spike bursts were accompanied by transient increases of the O2 consumption with parameters that correlated with burst magnitude and duration.ConclusionsControlled experimental manipulations of both the O2 level as well as the neuronal activity under in vivo-like conditions allowed to quantitatively relate spike discharge magnitudes in a particular neuronal circuitry with the O2 consumption in this area. Moreover, the possibility to distinctly manipulate various functional parameters will yield more insight in the coupling between metabolic and neuronal activity. Thus, apart from providing quantitative empiric evidence for the link between physiologically relevant spontaneous spike discharge in the brain and O2-dependent metabolism, isolated amphibian preparations are promising model systems to further dissociate the O2 dynamics in relation to neuronal computations.

Resting and field metabolic rates of Awassi sheep and Baladi goats raised by Negev bedouin

AbstractSheep are grazers and goats are intermediate feeders. By employing O2 consumption and heart rate measurements, resting metabolic rate (RMR) and field metabolic rate (FMR) were determined in four male fat-tailed Awassi sheep (44.0 ± 3.94) and four male Baladi goats (35.5 ± 5.42 kg) that were co-grazing natural pasture in the Negev Desert. There were 67.7 ± 3.75 g DM/m2 of herbaceous vegetation biomass, which was rapidly becoming senescent and more fibrous. We hypothesized that FMR of these desert-adapted ruminants would be relatively low when compared to other sheep and goat breeds, as animals in arid areas tend to have low metabolic rates. Both sheep (n = 6) and goats (n = 6) foraged 71% of the allotted 11 h free-pasture period; however, sheep grazed more than goats (P < 0.001); whereas goats browsed more than sheep (P < 0.001). RMR was higher (P = 0.007) in sheep than in goats (529 ± 23.5 v. 474 ± 25.4 kJ/kg0.75 BW/d), but FMR did not differ between species (618 ± 55.7 v. 613 ± 115.2 kJ/kg0.75 BW/d). In addition, the cost of activities, as a proportion of FMR, did not differ between sheep and goats; FMR increased by 89 kJ/kg0.75 BW/d or 17% in sheep and by 138 kJ/kg0.75 BW/d or 29% in goats. In comparing FMRs of sheep and goats in this study with these species in other studies, differences were inconsistent and, therefore, our hypothesis was not supported.

Lactic Acidosis in the Presence of Glucose Diminishes Warburg Effect in Lung Adenocarcinoma Cells.

Lactic acidosis (3 to 40 mM, pH < 6.9) is a condition found in solid tumors because tumor cells have a high rate of glucose consumption and lactate production even in the presence of oxygen; nevertheless, the microenvironment might still provide a sufficient glucose supply. Lactic acidosis has been proposed to shift metabolism from aerobic glycolysis toward oxidative phosphorylation (OXPHOS). We tested if lung tumor cells cultured under lactic acidosis shift their metabolism from glycolysis to OXPHOS by consuming extracellular lactate, increasing growth rate. We analyzed lung adenocarcinoma (A-549, A-427) cell lines and non-transformed fibroblast cells (MRC-5), which were cultured using RPMI-1640 medium initially containing lactate (2 mM) and glucose (10 mM), at pH 7.2 or 6.2 and oxygen tension 21% O2 (normoxia) or 2% O2 (hypoxia). We obtained growth curves, as well as glucose consumption and lactate production rates (measured during exponential growth) for each cell line. HIF-1α (Hypoxia-inducible factor 1 α), CS (citrate synthase) and AMPK (AMP-activated protein kinase) transcript levels were analyzed using RT-qPCR. By flow cytometry, we determined: (a) expression of glucose transporters (GLUT)1 and 4; (b) lactate transporters (MCT)1 and 4; (c) cell cycle profile, and (d) protein levels of HIF-1α, total and phosphorylated AMPK (pAMPK). Mitochondrial functionality was evaluated by measuring O2 consumption in tumor cells using polarography and a Clark-type electrode. Tumor and non-transformed cells used both aerobic glycolysis and OXPHOS for obtaining energy. As of 48 h of culture, lactate levels ranged from (4.5–14 mM), thus forming a lactic environment. Lactic acidosis diminished GLUT1/GLUT4 expression and glucose consumption in A-549, but not in A-427 cells, and induced differential expression of HIF-1α, AMPK, and CS transcripts. A-427 cells increased pAMPK and HIF-1α levels and shifted their metabolism increasing OXPHOS; thus supporting cell growth. Conversely, A-549 cells increased HIF-1α protein levels, but did not activate AMPK and diminished OXPHOS. A-549 cells survived by arresting cells in G1-phase. Our findings show that lactic acidosis diminishes Warburg effect in tumor cells, but this change does not necessarily promote a shift to OXPHOS. Hence, lung adenocarcinomas show a differential metabolic response even when they are under the same microenvironmental conditions.

Activation of AMP-activated protein kinase during sepsis/inflammation improves survival by preserving cellular metabolic fitness.

The purpose was to determine the role of AMPK activation in the renal metabolic response to sepsis, the development of sepsis-induced acute kidney injury (AKI) and on survival. In a prospective experimental study, 167 10- to 12-week-old C57BL/6 mice underwent cecal ligation and puncture (CLP) and human proximal tubule epithelial cells (TEC; HK2) were exposed to inflammatory mix (IM), a combination of lipopolysaccharide (LPS) and high mobility group box 1 (HMGB1). Renal/TEC metabolic fitness was assessed by monitoring the expression of drivers of oxidative phosphorylation (OXPHOS), the rates of utilization of OXPHOS/glycolysis in response to metabolic stress, and mitochondrial function by measuring O2 consumption rates (OCR) and the membrane potential (Δψm ). Sepsis/IM resulted in AKI, increased mortality, and in renal AMPK activation 6-24hours after CLP/IM. Pharmacologic activation of AMPK with 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) or metformin during sepsis improved the survival, while AMPK inhibition with Compound C increased mortality, impaired mitochondrial respiration, decreased OCR, and disrupted TEC metabolic fitness. AMPK-driven protection was associated with increased Sirt 3 expression and restoration of metabolic fitness. Renal AMPK activation in response to sepsis/IM is an adaptive mechanism that protects TEC, organs, and the host by preserving mitochondrial function and metabolic fitness likely through Sirt3 signaling.

Root O2 consumption, CO2 production and tissue concentration profiles in chickpea, as influenced by environmental hypoxia.

Roots in flooded soils experience hypoxia, with the least O2 in the vascular cylinder. Gradients in CO2 across roots had not previously been measured. The respiratory quotient (RQ; CO2 produced:O2 consumed) is expected to increase as O2 availability declines. A new CO2 microsensor and an O2 microsensor were used to measure profiles across roots of chickpea seedlings in aerated or hypoxic conditions. Simultaneous, nondestructive flux measurements of O2 consumption, CO2 production, and thus RQ, were taken for roots with declining O2 . Radial profiling revealed severe hypoxia and c.0.8kPa CO2 within the root vascular cylinder. The distance penetrated by O2 into the roots was shorter at lower O2 . The gradient in CO2 was in the opposite direction to that of O2 , across the roots and diffusive boundary layer. RQ increased as external O2 was lowered. For chickpea roots in solution at air equilibrium, O2 was very low and CO2 was elevated within the vascular cylinder; the extent of the severely hypoxic core increased as external O2 was reduced. The increased RQ in roots in response to declining external O2 highlighted the shift from respiration to ethanolic fermentation as the severely hypoxic/anoxic core became a progressively greater proportion of the root tissues.

The influence of low-frequency magnetic field regions on the Saccharomyces cerevisiae respiration and growth

The influence of four low-frequency magnetic field (MF) ranges 10–300 Hz, 10–100 Hz, 10–50 Hz and 50–100 Hz in scanning regime (all frequencies from selected range were scanned during 100 s repetitively during 24 h) on baker’s yeast cells Saccharomyces cerevisiae was examined by continuous measurements of cumulative O2 consumption and cumulative CO2 production over 24 h with Micro-Oxymax® respirometer. Besides respiration activity, measurements of cell growth and glucose uptake were performed as well. Statistical analysis indicated that, among all investigated low-frequency MF ranges, range from 10 Hz to 50 Hz had the greatest influence to yeast cell respiration and cell growth. More precisely, for this region, paired two sample one-tail t-test showed statistically significant differences in cumulative O2 consumption, cumulative CO2 production and S. cerevisiae cell number. Moreover samples exposed to MF range from 10 Hz to 50 Hz showed the same behavior in all five replicates: lower cumulative O2 consumption, higher cumulative CO2 production and higher cell number compared to control sample. This could be important from the application aspect, in industry (food, feed, brewery etc.) and biotechnology, because changes in cells metabolism are not caused by chemical treatment.

Modelling net energy of commercial cat diets.

Net energy accounts for the proportion of energy expenditure attributed to the digestion, metabolism, and absorption of ingested food. Currently, there are no models available to predict net energy density of food for domestic cats. Therefore, the objectives of this study were to measure the heat increment of feeding in cats, and to model the net energy of commercial diets. Metabolizable energy and calorimetry data from two previous studies was reanalyzed to create net energy models in the present study. Energy expenditure was calculated using measurements of CO2 production and O2 consumption. Net energy was determined as the metabolizable energy of the diets minus the heat increment of feeding. The heat increment of feeding was determined as the area under the energy expenditure curve above the resting fed metabolic rate. Eight net energy models were developed using metabolizable energy, 1 of 4 dietary parameters (crude protein, fat, fiber, and starch), and heat increment of feeding values from 0–2 h or 0–21 h. Two hours postprandial, and over the full calorimetry period, the heat increment of feeding amounted for 1.74, and 20.9% of the metabolizable energy, respectively. Of the models tested, the models using crude protein in combination with metabolizable energy as dietary parameters best fit the observed data, thus providing a more accurate estimate of dietary energy availability for cats.

3-Hydroxykynurenine bound to eye lens proteins induces oxidative modifications in crystalline proteins through a type I photosensitizing mechanism

Photosensitized reactions mediated by endogenous chromophores have been associated with the etiology of age-related cataract disease. Endogenous chromophores such as 3-hydroxykynurenine (3OHKN) can be found in both free form, and bound to crystallin proteins. However, their efficiency in generating photo-induced oxidative modifications on eye lens proteins is not completely understood. In this work, the efficiency and photodynamic activity of 3OHKN bound to both lysine (3OHKN-Lys) and bovine lens proteins (3OHKN-BLP) was assessed and compared with the photosensitizing activity of the major chromophore arising from glucose degradation (GDC). The photosensitizing activity of 3OHKN-Lys, 3OHKN-BLP and GDC was characterized by measurement of singlet oxygen quantum yields, O2 consumption, SDS-PAGE and amino acid analysis of the photo-oxidized proteins.Singlet oxygen quantum yields under 20% O2 atmosphere were 0.02, 0.01, and 0.27 for 3OHKN-Lys, 3OHKN-BLP and GDC, respectively. O2 consumption by photosensitized reactions was more efficient for 3OHKN-BLP, with the extent of O2 consumption being ∼28% higher than for 3OHKN-Lys and GDC under both 5 and 20% O2. SDS-PAGE showed that protein crosslinking is dependent on the O2 concentration, and more extensive at 5 than 20% O2. GDC and 3OHKN-Lys were the most efficient crosslinkers at 20 and 5% O2, respectively. Amino acid analysis of the irradiated proteins showed consumption of Trp, His, Tyr and Phe, and formation of kynurenine (from Trp), methionine sulfoxide (from Met) and DOPA (from Tyr). Kynurenine formation was dependent on the O2 concentration with higher amounts detected at 5 than 20% O2 for 3OHKN-BLP and 3OHKN-Lys, with 3OHKN-BLP the most efficient sensitizer. Our results suggest that 3OHKN-BLP can elicit photo-oxidative damage mainly by a type I photosensitizing mechanism, with this likely to be the most prevalent pathway at the low physiologic O2 concentrations in the eye lens.

Effect of TNFα on Mitochondrial Function and Mitochondrial Biogenesis in Human Airway Smooth Muscle

Airway inflammation is a key aspect of asthma and is associated with airway smooth muscle (ASM) hyperreactivity as well as airway remodeling. Proinflammatory cytokines, such as TNFα mediate this airway inflammatory response. Previously, we found that TNFα induces an increase airway smooth muscle (ASM) force and ATP hydrolysis. In response, TNFα may also induce an increase in ATP production in ASM. This could be achieved by either an increase in mitochondrial function and/or mitochondrial biogenesis. We previously found that TNFα decreases mitochondrial Ca2+ influx. Since dehydrogenase enzymes in the TCA cycle are Ca2+ dependent, this would tend to reduce mitochondrial function in response to agonist stimulation. We also found that TNFα increases mitochondrial fragmentation, an initial step in mitochondrial biogenesis. We hypothesized that TNFα increases mitochondrial biogenesis and decreases mitochondrial function in human ASM.Human ASM cells were isolated from lung specimens incidental to patient surgery. The patients were normal as evaluated by a clinical pathologist (no history of asthma or COPD). hASM cells were exposed to TNFα (20 ng/ml) for 24 h. To examine mitochondrial biogenesis, protein expression of porin (an indicator of mitochondrial density) and PGC1α (a regulator of mitochondria biogenesis) were determined by Western blot analysis. In addition, the relative number of copies of human mitochondrial DNA (mtDNA) was determined by PCR and normalized to nuclear DNA. Mitochondrial function was assessed by measuring O2 Consumption Rate (OCR – using a Seahorse Bioscience XF24 Analyzer), succinate dehydrogenase (SDH) activity (using a quantitative histochemical technique) and mitochondrial membrane potential – (DYm – using TMRM and confocal microscopy). OCR and SDH activity measurements were normalized to mitochondrial volume density. Results were analyzed by one‐way ANOVA with post hoc analysis when justified.We found that TNFα increases mitochondrial biogenesis as indicated by an increase in porin and PGC1α protein expression in hASM and an increase in mtDNA copy numbers. We also found that TNFα decreases mitochondrial membrane potential in hASM cells, and also decreases OCR and SDH activity when normalized for the increase in mitochondrial volume density induced by TNFα. In a normal homeostatic response, an increase in hASM force and ATP hydrolysis (energy demand) would be met by increased mitochondrial ATP production. Our results indicate that TNFα disrupts this normal homeostatic response by reducing mitochondrial Ca2+ influx and thereby reducing mitochondrial TCA activity. However, TNFα increase the number of mitochondria to compensate the decrease in mitochondrial TCA activity.Support or Funding InformationSupported by NIH grant HL126451This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Septic Shock Alters Mitochondrial Respiration of Lymphoid Cell-Lines and Human Peripheral Blood Mononuclear Cells: The Role of Plasma

In septic shock patients, postseptic immunosuppression state after the systemic inflammatory response syndrome is responsible for nosocomial infections, with subsequent increased mortality. The aim of the present study was to assess the underlying cellular mechanisms of the postseptic immunosuppression state, by investigating mitochondrial functions of peripheral blood mononuclear cells (PBMCs) from septic shock patients over 7 days. Eighteen patients admitted to a French intensive care unit for septic shock were included. At days 1 and 7, PBMCs were isolated by Ficoll density gradient centrifugation. Mitochondrial respiration of intact septic PBMCs was assessed versus control group PBMCs, by measuring O2 consumption in plasma, using high-resolution respirometry. Mitochondrial respiration was then compared between septic plasmas and control plasmas for control PBMCs, septic PBMCs, and lymphoid cell-line (CEM). To investigate the role of plasma, we measured several plasma cytokines, among them High-Mobility Group Box 1 (HMGB1), by enzyme-linked immunosorbent assays. Basal O2 consumption of septic shock PBMCs was of 8.27 ± 3.39 and 10.48 ± 3.99 pmol/s/10 cells at days 1 and 7, respectively, significantly higher than in control PBMCs (5.37 ± 1.46 pmol/s/10 cells, P < 0.05). Septic patient PBMCs showed a lower response to oligomycin, suggesting a reduced ATP-synthase activity, as well as an increased response to carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP) suggesting an increased mitochondrial respiratory capacity. At 6 h, septic plasmas showed a decreased O2 consumption of CEM (4.73 ± 1.46 vs. 6.58 ± 1.53, P < 0.05) as well as in control group PBMCs (1.76 ± 0.36 vs. 2.70 ± 0.42, P < 0.05), and triggered a decreased ATP-synthase activity but an increased response to FCCP. These differences are not explained by different cell survival. High HMGB1 levels were significantly associated with reduced PBMCs mitochondrial respiration. Septic plasma impairs mitochondrial respiration in immune cells, with a possible role of the proinflammatory protein HMGB1, leading to a subsequent compensation, probably by enzymatic activation. This compensation result is an improvement of global mitochondrial respiratory capacity, but without restoring ATP-synthase activity.

Longitudinal Measurements of Resting Energy Expenditure by Indirect Calorimetry in Healthy Term Infants during the First 2 Months of Life.

To determine longitudinal measurements of resting energy expenditure (REE) by indirect calorimetry (IC) in healthy term infants during the first 2 months of life. An outpatient prospective pilot study was performed in healthy term infants to estimate REE by measuring expired gas fractions of oxygen (O2) and carbon dioxide (CO2) with IC in a respiratory and metabolic steady state. A total of 30 measurements were performed. Fourteen subjects completed measurements at both 1 and 2 months of life, and two subjects had only measurements made at 1 month of life. Mean REE values were 64.1 ± 12.7 and 58.4 ± 14.3 kcal/kg/d at 1 and 2 months of age, respectively. Mean O2 consumption and CO2 production measurements were 9.3 ± 2.0 and 7.7 ± 1.2 mL/kg/min and 8.1 ± 2.2 and 6.4 ± 1.1 mL/kg/min at 1 and 2 months of age, respectively. This pilot study demonstrates longitudinal measurements of REE by IC in healthy term infants during the first 2 months of life. We also demonstrate that, overall, there is consistency in REE values in this population, with a likely decrease in individual longitudinal measurements over the first 2 months of life.

Influences of maternal nutrient restriction and arginine supplementation on visceral metabolism and hypothalamic circuitry of offspring

Maternal nutrient restriction during gestation can exert long-term negative effects on offspring health and performance. Arginine supplementation may rescue some of the negative effects elicited by maternal nutrient restriction. We tested the hypothesis that maternal arginine supplementation during gestation would rescue deleterious effects of nutrient restriction on in vitro O2 consumption in the liver and jejunum and hypothalamic protein expression of proopiomelanocortin (POMC), neuropeptide Y (NPY), agouti-related peptide (AgRP), and neuronal nitric oxide synthase (nNOS), and the colocalization of nNOS and active phosphor-signal transducer and activator of transcription 3 (pSTAT3) in female offspring. Multiparous ewes were assigned to dietary treatment at 54 d of gestation: 100% of requirements (Con), 60% of control (Res), or Res plus rumen-protected arginine (Res-Arg; 180 mg/kg). At parturition, offspring were immediately removed from their dam and placed on a common diet. At 54 ± 4 d of age, female lambs (n = 6 per treatment) were weighed, the liver and jejunum were weighed, and samples were collected for in vitro measurement of O2 consumption. The hypothalamus was collected to determine protein expression of POMC, NPY, AgRP, and nNOS, and the colocalization of nNOS and pSTAT3 (n = 3, 4, and 4 for Con, Res, and Res-Arg, respectively). Hepatic consumption of O2 in vitro (mol/min/liver) was decreased (P = 0.04) in the Res and Res-Arg group compared with Con. Intensity of staining for NPY-containing fibers tended to decrease (P = 0.10) in Res and Res-Arg compared with Con. Number of POMC neuronal cells in the arcuate nucleus (ARC) of the hypothalamus decreased (P ≤ 0.03) in the Res group compared with Res-Arg. These observations demonstrate that maternal nutrient restriction decreases energy utilization in the liver and number of POMC cells in the ARC of offspring. Supplementation of arginine to the gestating ewe failed to influence hepatic use of energy in lambs from Res ewes. Numbers of POMC-containing cells were increased in the ARC in lambs from ewes restricted to 60% of nutritional requirements and supplemented with rumen-protected arginine, potentially influencing feeding behavior and hepatic energy metabolism.

Determination of net energy content of soybean oil fed to growing pigs using indirect calorimetry.

The objectives of this experiment were: (i) to determine the net energy (NE) of soybean oil (SBO) fed to growing pigs using indirect calorimetry (IC); and (ii) to evaluate the effects of inclusion rate of SBO on heat production, oxidative status and nutrient digestibility in growing pigs. Eighteen growing barrows were allotted to three diets based on completely randomized design with six replicate pigs (period) per diet. Diets included a corn-soybean meal basal diet and two test diets containing 5% or 10% SBO at the expense of corn and soybean meal. During each period, pigs were individually housed in metabolism crates for 14days, including 7days to adapt to feed, metabolism crate and environmental conditions. On day 8, pigs were transferred to the open-circuit respiration chambers for measurement of daily O2 consumption and CO2 and CH4 production. During this time, pigs were fed one of the three diets at 2.4MJ metabolizable energy/kg body weight (BW)0.6 /day. Total feces and urine were collected and daily total heat production (THP) was measured from days 9 to 13 and fasted on day 14 to evaluate their fasting heat production (FHP). The results show that trends of decreased apparent total tract digestibility of neutral detergent fiber (linear, P=0.09) and acid detergent fiber (linear, P=0.07) were observed as the content of dietary lipids increased. The average THP for the three diets were 1326, 1208 and 1193kJ/kg BW0.6 /day, respectively. The FHP of pigs averaged 843kJ/kg BW0.6 /day and was not affected by diet characteristics. A reduction of the respiratory quotients in the fed state as the inclusion level of SBO increased was observed. In conclusion, the NE values of SBO we determined by indirect calorimetry were 33.45 and 34.05MJ/kg dry matter under two inclusion levels. THP could be largely reduced when SBO is added in the feed, but the THP of SBO included at 5% in a corn-soybean meal diet is not different from the THP of SBO included at 10%.

Mitochondrial function in engineered cardiac tissues is regulated by extracellular matrix elasticity and tissue alignment.

Mitochondria in cardiac myocytes are critical for generating ATP to meet the high metabolic demands associated with sarcomere shortening. Distinct remodeling of mitochondrial structure and function occur in cardiac myocytes in both developmental and pathological settings. However, the factors that underlie these changes are poorly understood. Because remodeling of tissue architecture and extracellular matrix (ECM) elasticity are also hallmarks of ventricular development and disease, we hypothesize that these environmental factors regulate mitochondrial function in cardiac myocytes. To test this, we developed a new procedure to transfer tunable polydimethylsiloxane disks microcontact-printed with fibronectin into cell culture microplates. We cultured Sprague-Dawley neonatal rat ventricular myocytes within the wells, which consistently formed tissues following the printed fibronectin, and measured oxygen consumption rate using a Seahorse extracellular flux analyzer. Our data indicate that parameters associated with baseline metabolism are predominantly regulated by ECM elasticity, whereas the ability of tissues to adapt to metabolic stress is regulated by both ECM elasticity and tissue alignment. Furthermore, bioenergetic health index, which reflects both the positive and negative aspects of oxygen consumption, was highest in aligned tissues on the most rigid substrate, suggesting that overall mitochondrial function is regulated by both ECM elasticity and tissue alignment. Our results demonstrate that mitochondrial function is regulated by both ECM elasticity and myofibril architecture in cardiac myocytes. This provides novel insight into how extracellular cues impact mitochondrial function in the context of cardiac development and disease.NEW & NOTEWORTHY A new methodology has been developed to measure O2 consumption rates in engineered cardiac tissues with independent control over tissue alignment and matrix elasticity. This led to the findings that matrix elasticity regulates basal mitochondrial function, whereas both matrix elasticity and tissue alignment regulate mitochondrial stress responses.

Adolescent children born preterm have altered cardiac regulation during and immediately following maximal exercise

IntroductionHeart rate recovery (HRR) after maximal exercise has been shown to be a marker of fitness and disease status. Individuals born prematurely exhibit increased left ventricular mass and reduced end systolic and end diastolic volume. It has been shown that slower HRR is correlated with a higher risk for cardiovascular disease. Oxygen (O2) pulse is defined as the total volume of oxygen consumed per heartbeat and a low O2 pulse has been associated with pulmonary hypertension (PH) and other cardiovascular (CV) diseases. It is correlated with stroke volume and overall cardiovascular efficiency during exercise. The purpose of our research was to investigate the long‐term effects of preterm birth on HRR immediately following maximal exercise, and we hypothesized that it would be slower in adolescents born preterm.MethodsFifteen children 12–13 years old, 8 born preterm (birthweight &lt;1500 g, gestational age &lt;32 weeks) and 7 children born full term (gestational age 38–40 weeks) underwent progressive maximal exercise testing on a cycle ergometer, with continuous measurement of O2 consumption (ml/kg/min) and heart rate (HR), as well as cardiac output (Q), stroke volume (SV) using thoracic bioimpedance. SV and Q were indexed to body surface area (BSA (m2), SVi and Qi). HR was recorded for 2 minutes of rest following maximal exercise and HRR was the absolute drop in HR at 2 minutes from maximal HR (HRR2min). Statistical analysis was done using multiple t‐tests and linear regression.ResultsHRR2min following maximal exercise was lower in preterms than controls (54.4 ± 4.2 v 63.5 ± 5.9, p=0.01, respectively). Preterm subjects had lower relative maximal oxygen consumption (VO2max) compared to control subjects (39.6 ± 9.3 v 52.8 ± 7.3 ml/kg/min, p=0.03). The increase in O2 pulse from rest to maximal exercise was greater in controls compared to the preterms (8.8 ± 1.1 v 4.8 ± 3.0 ml O2/beat, p=0.02). SVi did not increase significantly in preterms from rest to maximal exercise (51.7 ± 9.0 v 53.3 ± 8.3 ml/m2, p=0.77), but SV significantly increased in controls from rest to maximal exercise (47.4 ± 4.0 v 51.3 ± 8.4 ml/m2, p=0.01). Furthermore, the change in SVi (ΔSVi) from rest to maximal exercise was significantly smaller in preterms than in controls (0.0 ± 7.2 v 20.3 ± 17.0 ml/m2, p=0.012). A simple linear regression showed a positive relationship between ΔSV and HRR (p=0.03, r2=0.39).DiscussionWe found that multiple measurements associated with cardiac regulation were significantly different in preterms compared with controls. A slower HRR has been correlated with PH risk and CV disease that could lead to future complications. The inability to augment SV during exercise is uncommon, and has been noted in patients with CV disease. Finally, the positive relationship between ΔSVi and HRR after exercise indicates that there may be a direct relationship between the two variables. We have demonstrated that multiple cardiac parameters are altered in adolescent children born preterm during and immediately following exercise. There appears to be an altered cardiac regulation mechanism in adolescent children born preterm, and this will be an important area of study in the future.Support or Funding InformationNational Institutes of Health: 1R01 HL086897 (M.W.E.) and R01 HL38149 (M.P.).

Measuring Antioxidant Activity in Bioorganic Samples by the Differential Oxygen Uptake Apparatus: Recent Advances

The measure of O2 consumption during the inhibited autoxidation of an easily oxidizable substrate is one of the most reliable and predictive methods to assess antioxidant activity, especially for structure-activity relationship studies, for food and industrial applications. The differential oxygen uptake apparatus described herein represents a powerful and cost-effective way to obtain antioxidant activity from inhibited autoxidation studies. These experiments provide the rate constant and the stoichiometry of the reaction between antioxidants and peroxyl radicals (ROO∙), which are involved in the propagation of radical damage. We show the operation principles and the utility of this instrumentation in the bioorganic laboratory, with regard to the recent advances in this field, ranging from the study of natural antioxidants in biomimetic system, to the use of substrates generating hydroperoxyl radicals, and to the evaluation of novel nanoantioxidants.

Exploring Selective, Efficient 2 e- and 4 e- Electrochemical Oxygen Reduction Using Electrocatlayts Based on Reduced Graphene Oxide

Recently, nitrogen-doped carbon materials, such as N-doped reduced graphene oxide (N-rGO), have been significantly studied due to their outstanding ORR performance, which some studies find rivals that of Pt. Generally the electroreduction of oxygen can proceed through one of two overall reactions: a 4e- process to convert from O2 to H2O, and a 2e- process to form H2O2. There is general agreement that nitrogen-defects selectively catalyze the more thermodynamically favored 4e- mechanism over the 2e-process. However, a distribution of different N-defect sites (pyridinic, pyrollic, graphitic) is typically observed in N-doped carbon materials and there is still no consensus regarding the role of each site on the ORR mechanism. In this study, we use a straightforward, low temperature and pressure procedure to synthesize N-rGO and rGO and compare the resultant materials’ electrocatalytic behavior with rGO and N-rGO synthesized using more traditional high-temperature procedures. Briefly, the low temperature and pressure synthesis was conducted at 100 oC and atmospheric pressure using NH4OH as both the reducing and N-doping agent in a well-dispersed graphene oxide (GO) solution. This method results in materials with a distribution of the three nitrogen defect sites and reasonably high N-doping content (~6 atomic percent), as confirmed by structural analysis including XPS and TGA. The resulting materials could be further annealed at high temperatures (over 400 oC) under inert condition to modify the nitrogen and carbon defect distribution. Similar synthesis procedures were used to prepare non-N-doped rGO samples to elucidate the importance of N-sites. We have characterized electrocatalytic selectivity by monitoring O2 pressure decay in well-stirred, modified electrochemical H-cells with a calibrated, known headspace volume. We also quantify H2O2 formation using a standard iodometric titration on the electrolyte. These techniques provide direct measurements of O2 consumption and H2O2 formation during ORR and are therefore more accurate than traditional rotating ring disk electrode measurements. Both acid (0.1 M H2SO4) and base (0.1 M KOH) conditions have been explored. We have found that certain variants of N-rGO and rGO display exceptionally selective (~100%) and efficient (nearly no onset overpotential) formation of H2O2 in basic conditions. Thermal annealing changes both the N-site distribution and reaction selectivity and efficiency. Furthermore, higher overpotentials for product formation are observed in acid solutions compared to basic solutions. Results will be discussed linking the selectivity and efficiency of the oxygen reduction reaction to the role of nitrogen and carbon defects in N-rGO and rGO.

The significance of respiration timing in the energetics estimates of free-ranging killer whales (Orcinus orca).

Respiration rate has been used as an indicator of metabolic rate and associated cost of transport (COT) of free-ranging cetaceans, discounting potential respiration-by-respiration variation in O2 uptake. To investigate the influence of respiration timing on O2 uptake, we developed a dynamic model of O2 exchange and storage. Individual respiration events were revealed from kinematic data from 10 adult Norwegian herring-feeding killer whales (Orcinus orca) recorded with high-resolution tags (DTAGs). We compared fixed O2 uptake per respiration models with O2 uptake per respiration estimated through a simple 'broken-stick' O2-uptake function, in which O2 uptake was assumed to be the maximum possible O2 uptake when stores are depleted or maximum total body O2 store minus existing O2 store when stores are close to saturated. In contrast to findings assuming fixed O2 uptake per respiration, uptake from the broken-stick model yielded a high correlation (r(2)>0.9) between O2 uptake and activity level. Moreover, we found that respiration intervals increased and became less variable at higher swimming speeds, possibly to increase O2 uptake efficiency per respiration. As found in previous studies, COT decreased monotonically versus speed using the fixed O2 uptake per respiration models. However, the broken-stick uptake model yielded a curvilinear COT curve with a clear minimum at typical swimming speeds of 1.7-2.4 m s(-1) Our results showed that respiration-by-respiration variation in O2 uptake is expected to be significant. And though O2 consumption measurements of COT for free-ranging cetaceans remain impractical, accounting for the influence of respiration timing on O2 uptake will lead to more consistent predictions of field metabolic rates than using respiration rate alone.

Climate change and the loss of organic archaeological deposits in the Arctic.

The Arctic is warming twice as fast as the global average with overlooked consequences for the preservation of the rich cultural and environmental records that have been stored for millennia in archaeological deposits. In this article, we investigate the oxic degradation of different types of organic archaeological deposits located in different climatic zones in West and South Greenland. The rate of degradation is investigated based on measurements of O2 consumption, CO2 production and heat production at different temperatures and water contents. Overall, there is good consistency between the three methods. However, at one site the, O2 consumption is markedly higher than the CO2 production, highlighting the importance of combining several measures when assessing the vulnerability of organic deposits. The archaeological deposits are highly vulnerable to degradation regardless of age, depositional and environmental conditions. Degradation rates of the deposits are more sensitive to increasing temperatures than natural soils and the process is accompanied by a high microbial heat production that correlates significantly with their total carbon content. We conclude that organic archaeology in the Arctic is facing a critical challenge that requires international action.

Microbial bioavailability of dissolved organic carbon from leachates of freshwater autotrophs

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 76:233-241 (2016) - DOI: https://doi.org/10.3354/ame01782 Microbial bioavailability of dissolved organic carbon from leachates of freshwater autotrophs Stephen D. Shivers1,2,*, Stephen P. Opsahl2,3, Alan P. Covich1 1Institute of Ecology, Odum School of Ecology, University of Georgia, Athens, GA 30602, USA 2Joseph W. Jones Ecological Research Center, 3988 Jones Center Drive, Newton, GA 39870, USA 3Present address: USGS Texas Water Science Center, U.S. Geological Survey, 5563 De Zavala Road, Suite 290, San Antonio, TX 78249, USA *Corresponding author: sshivers@jonesctr.org ABSTRACT: The concentration and bioavailability of dissolved organic carbon (DOC) released during senescence of aquatic vegetation varies among autotrophs, and the corresponding response by microbial communities depends on DOC bioavailability. To evaluate microbial response to different leachate sources, experiments that measured O2 consumption, utilization of DOC and monosaccharides, and the specific absorbance of light at 350 nm (SUVA350) were conducted on leachates from 3 primary producers. Specific absorbance at 350 nm (SUVA350) increased in 2 of 3 experiments. Increases in SUVA350 are consistent with the preferential use of labile DOC with a lower SUVA350. However, similar patterns of monosaccharide and DOC utilization do not support the hypothesis of preferential usage of labile carbohydrates over bulk DOC by the microbial community over the 8 d study. Monosaccharides appear to represent only a portion of a larger pool of labile DOC constituents that are found in autotrophic leachates that can be taken up more rapidly than metabolized by microbial communities. O2 consumption by the microbial community varied significantly among leachate types but was relatively high during the early phase of the experiments in all leachates. Similarly, DOC uptake was relatively rapid during the early phase of the experiments. The microbial uptake of DOC relative to the consumption of dissolved oxygen, expressed as a ratio, ranged from 2.31 to 3.95 during the initial 24 h period but approached 1:1 over the duration of the experiment. These ratios suggest that ‘luxury uptake’ of DOC by microbial communities might have occurred in the initial phase of the experiment. KEY WORDS: Dissolved organic carbon · Bioavailability · Monosaccharides · Leachates · Luxury uptake · Hydrilla verticillata · Potamogeton illinoensis · Lyngbya Full text in pdf format PreviousNextCite this article as: Shivers SD, Opsahl SP, Covich AP (2016) Microbial bioavailability of dissolved organic carbon from leachates of freshwater autotrophs. Aquat Microb Ecol 76:233-241. https://doi.org/10.3354/ame01782 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 76, No. 3. Online publication date: February 22, 2016 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2016 Inter-Research.