Aerobic Enzyme Activity Research Articles

Naringenin promotes the expression of oxidized myofibers via the PKA signaling pathway in C57BL/6J mice and C2C12 cells

Naringenin, a citrus-derived flavonoid, has been reported to positively exert skeletal muscle function. The study designed to explore the potential role and mechanisms of naringenin on regulating the expression of oxidized myofibrils in mice and C2C12 myotubes. In this study, we found that naringenin supplementation significantly improved exercise endurance and oxygen consumption of mice, and also increased aerobic enzyme activity and oxidative myofibers expression in skeletal muscle and C2C12 cells. Meanwhile, naringenin activated the expression of p-PKA/PKA, p-LKB1/LKB1, p-AMPK/AMPK and PGC-1α in skeletal muscle. Furthermore, in vitro studies shown that inhibition of PKA, LKB1 and AMPK could attenuate naringenin-regulated increase in slow muscle fiber proteins. This study suggests that naringenin supplementation can enhance slow myofiber expression by activating the PKA signaling pathway in C57BL/6J mice and C2C12 myotubes. These findings provide a new application of naringenin as a natural candidate to regulate oxidized fiber types and endurance of skeletal muscle.

Cardiovascular oxygen transport and peripheral oxygen extraction capacity contribute to acute heat tolerance in European seabass

This study evaluated whether different parameters describing cardiovascular function, energy metabolism, oxygen transport and oxidative stress were related to the critical thermal maximum (CTMAX) of European seabass (Dicentrarchus labrax) and if there were differential changes in these parameters during and after heat shock in animals with different CTMAX in order to characterize which physiological features make seabass vulnerable to heat waves. Seabass (n = 621) were tested for CTMAX and the physiological parameters were measured in individuals with good or poor temperature tolerance before and after a heat shock (change in temperature from 15 °C to 28 °C in 1.5 h). Fish with good thermal tolerance had larger ventricles with higher maximal heart rate during the heat shock than individuals with poor tolerance. Furthermore, they initially had a high ventricular Ca2+-ATPase activity, which was reduced to a similar level as in fish with poor tolerance following heat shock. The activity of heart lactate dehydrogenase increased in fish with high tolerance, when they were exposed to heat shock, while the aerobic enzyme activity did not differ between groups. The tolerant individuals had smaller red muscle fibers with higher myoglobin content than the poorly tolerant ones. The poorly tolerant individuals had higher hematocrit, which increased with heat shock in both groups. The poorly tolerant individuals had also higher activity of enzymes related to oxidative stress especially after heat shock. In general, CTMAX was not depending on merely one physiological factor but several organ and cellular parameters were related to the CTMAX of seabass and when working in combination they might protect the highly tolerant seabass from future heat waves.

Luteolin increases slow muscle fibers via FLCN-AMPK-PGC-1α signaling pathway

• Luteolin may improve endurance exercise capacity of mice. • Luteolin may increase slow muscle fibers proportion both in mice and C2C12 myotubes. • Luteolin may activate FLCN-AMPK-PGC-1α axis in mice’s muscle and C2C12 myotubes. • FLCN-AMPK-PGC-1α axis may play key role in luteolin induced slow myofibers increasing. While the regulating mechanisms of slow myofibers have been gradually explored, there are currently a lack of effective means to increase slow myofibers proportion. Here, we have showed that luteolin could markedly improve endurance exercise performance and increase body oxygen consumption of mice, and activate aerobic enzyme activity and slow myofibers related genes and proteins expression in mice’s skeletal muscle. Meanwhile, folliculin (FLCN)-AMP-activated protein kinase (AMPK) -peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) pathway was activated by treatment luteolin in the tissues. Furthermore, by in vitro investigation and FLCN lentivirus infection, we have found that the over-expression of FLCN significantly reduces the effects of luteolin on slow myofibers expression and AMPK-PGC-1α axis activation. Together, our results indicate that luteolin can increase the proportion of slow myofibers probably by FLCN-AMPK-PGC-1α pathway. These findings provide a novel approach to increase slow muscle fibers proportion and improve skeletal muscle fitness.

Red and white muscle proportions and enzyme activities in mesopelagic sharks.

In the last decade, there has been an increase in the study of the ecology of deep-sea organisms. One way to understand an organism's ecology is the study of its metabolism. According to literature, deep-sea sharks possess a lower anaerobic enzyme activity than their shallow-water counterparts, but no difference has been observed regarding their aerobic enzyme activities. These studies have suggested deep-sea sharks should be slow and listless swimmers. However, other studies based on video observations have revealed differences in cruise swimming speed between different species. The present study examined muscles of squaliform sharks, including both luminous and non-luminous species. We combined measurements of the relative amounts of red and white muscle with assays of enzymes that are used as markers for aerobic (citrate synthase, malate dehydrogenase) and anaerobic (lactate dehydrogenase) metabolism, searching for a relationship with cruising speeds. Non-luminous deep-sea species displayed lower aerobic enzyme activities but similar anaerobic enzyme activities than the benthic shallow-water counterpart (Squalus acanthias). Conversely, luminous Etmopteridae species were found to have similar aerobic enzyme activities to S. acanthias but displayed lower anaerobic enzyme activities. Analyses revealed that red muscle proportion and aerobic enzyme activities were positively related to the cruise swimming speed. In contrast, Dalatias licha, which swims at the slowest cruise swimming speed ever recorded, presented a very low aerobic metabolic phenotype (lower aerobic marker enzymes and less red muscle). Finally, the values obtained for white muscle proportion and anaerobic metabolic phenotype suggested a high burst capacity for D. licha and non-luminous sharks.

Naringin Promotes Skeletal Muscle Fiber Remodeling by the AdipoR1-APPL1-AMPK Signaling Pathway.

Naringin, a natural flavonoid mainly found in citrus fruit, has been reported to exert a positive effect on improving skeletal muscle health. However, the effects and potential mechanisms of naringin on skeletal muscle fiber switching is still unclear. Here, we discovered that oral administration of naringin increased the low-speed running time, four-limb hanging time, body oxygen consumption in mice, enhanced aerobic enzyme activity, MyHC I expression, and slow-twitch fiber percentage in mice skeletal muscle. By contrast, naringin decreased α-GPDH enzyme activity, MyHC IIb expression, and fast-twitch fiber percentage. Moreover, naringin increased the concentration of serum adiponectin and activated the expression of AdipoR1, APPL1, AMPK, and PGC-1α. Furthermore, by the in vitro experiment and AdipoR1 knockdown, we found that inhibition of the AdipoR1 signaling pathway significantly reduced the effect of naringin on slow-twitch fiber-/fast-twitch fiber-related gene and protein expression. In conclusion, our results indicated that naringin could induce skeletal muscle fiber transition from fast twitch to slow twitch via the AdipoR1 signaling pathway. This study may provide new strategy for improving exercise endurance and slow muscle fiber deficiency-related diseases.

Physiological insights for aquaculture diversification: Swimming capacity and efficiency, and metabolic scope for activity in cojinoba Seriolella violacea

Aquaculture diversification is important for providing sustainable sources of food fish amidst changing environments, pathogens, economies, and market demand. Particularly for newly cultured species where information may be limited, optimization of culture practices relies on an understanding of the physiology and ecology of a species. The cojinoba (Seriolella violacea; Centrolophidae), a coastal pelagic marine fish, is a species of growing importance for aquaculture production in South America. Although methods for breeding and larval to juvenile rearing have been established, little is known about the physiology of this species. Therefore, measures of metabolism, swimming capacity and efficiency, red:white (R:W) muscle ratios, and associated aerobic and anaerobic biochemical parameters, such as plasma glucose and lactate, and muscle enzyme activities (i.e., pyruvate kinase, citrate synthase, electron transport system [ETS]), were measured. For cojinoba at 15 °C with mean body length (BL; total length) of 22 cm, critical swimming velocity (Ucrit) was approximately 80 cm/s or 3.8 BL/s, and optimal swimming velocity (Uopt) was 50 cm/s or 2.3 BL/s. Aerobic scope for metabolism was approximately 300 mg O2/kg/h, with Mo2 max 3.4 fold greater than standard metabolic rate. Swimming was facilitated by linear increases in tail beat frequency until burst and glide swimming initiated near Ucrit. At low velocities, large (~20% BL) pectoral fins were used for propulsion and maneuverability/maintaining equilibrium; beat frequency diminished rapidly with increasing velocity. Red:white muscle ratios at 50% BL and 75% BL (caudal peduncle) were comparable to other ectothermic species, with a greater proportion of red muscle in the caudal peduncle presumably corresponding to facilitation of sustained pelagic swimming. Plasma glucose and lactate were elevated at Ucrit by 20% and 45% respectively, indicating mobilization of anaerobic energy sources at fatigue. Aerobic enzyme activities were much higher in red muscle, the ratio of anaerobic:aerobic enzyme activity was higher in white muscle, and ETS activities decreased at fatigue in both red and white muscle. The cojinoba has a moderate metabolic rate compared to other pelagic species, displays shoaling behavior, is maneuverable at low velocities due to pectoral fin use, but has optimal swimming efficiencies at higher velocities. These factors are beneficial for designing culture systems to promote exercise benefits for growth and welfare.

Energy Conservation Strategies in an Indian Air-Breathing Catfish, Heteropneustes Fossilis, in Conditions of Hypoxia

Low oxygen concentration is a common feature occurring in a wide range of aquatic systems and in varied ranges depending upon temporal frequency, seasonality and persistence of a place. There have always been naturally occurring low oxygen condition in freshwaters of tropical countries like India. Moreover, anthropogenic activities, related primarily to organic and nutrient enrichment, have led to increase in hypoxia and anoxia both in fresh and in marine system. The fishes in a tropical country like India are quite frequently exposed to this. Aquatic organisms which are frequently exposed to hypoxia show adaptations at all the three levels, namely behavioural, morphological and physiological. To assess the effect of hypoxia at physiological level, change in anaerobic and aerobic enzyme activities and protein profiling in selected tissues of air-breathing catfish, Heteropneustes fossilis, was undertaken. Fish were exposed to experimentally provoked hypoxia for different durations and were killed to study the effect of hypoxia on selected enzymes activities in heart, liver, brain and muscle. Significant changes were recorded. The observations indicated that different tissues respond differently to the stress of hypoxia and the enzyme activity responds in a tissue-specific manner.

Comparison of respiration rate and electron transport system (ETS) enzyme-mediated reduction assay of the invasive copepod Eurytemora carolleeae Alekseev & Souissi, 2011 (Calanoida, Temoridae) in Green Bay, WI, U.S.A.

Abstract Anthropogenic activities can cause important changes in aquatic ecosystems, such as warming due to climate change, nutrient loading from agricultural runoff and urban areas, and decreased concentrations of oxygen in bottom waters. These changes may lead to impacts on both organism performance and ecosystem functionality. Studying planktonic species that form an aquatic ecosystem’s foundation is an important step towards understanding the entire food web and predicting how it may respond to a changing environment. One important planktonic species in the Laurentian Great Lakes is the invasive calanoid copepod Eurytemora carolleeae (formerly considered part of the Eurytemora affinis species complex). This study analyzes the metabolic activity of E. carolleeae from Green Bay, Lake Michigan, U.S.A. using two different methods, over a range of temperatures from 9 to 26°C. Total oxygen consumption was measured directly using a micropulse oxygen probe system, and the activity of aerobic metabolic enzymes in the electron transport system (ETS) was quantified using in vitro reduction of iodonitrotetrazolium chloride (INT). Respiration rate of E. carolleeae increases approximately linearly from 9 to 26°C. Measurements of ETS activity indicate that the copepod’s metabolic enzymes have an Arrhenius activation energy of 46.5 ± 15.6 kJ/mol with a thermal maximum between 22 and 26°C. Overall, E. carolleeae ETS rates increased by approximately 7% per °C over the range 9 to 22°C. This thermal limit has implications for future performance of this species, as the combination of higher temperatures and disappearance of oxygenated colder-water refuges may limit E. carolleeae’s success in the Green Bay system following warmer climate and increased nutrient conditions.

Succinate induces skeletal muscle fiber remodeling via SUNCR1 signaling.

The conversion of skeletal muscle fiber from fast twitch to slow‐twitch is important for sustained and tonic contractile events, maintenance of energy homeostasis, and the alleviation of fatigue. Skeletal muscle remodeling is effectively induced by endurance or aerobic exercise, which also generates several tricarboxylic acid (TCA) cycle intermediates, including succinate. However, whether succinate regulates muscle fiber‐type transitions remains unclear. Here, we found that dietary succinate supplementation increased endurance exercise ability, myosin heavy chain I expression, aerobic enzyme activity, oxygen consumption, and mitochondrial biogenesis in mouse skeletal muscle. By contrast, succinate decreased lactate dehydrogenase activity, lactate production, and myosin heavy chain IIb expression. Further, by using pharmacological or genetic loss‐of‐function models generated by phospholipase Cβ antagonists, SUNCR1 global knockout, or SUNCR1 gastrocnemius‐specific knockdown, we found that the effects of succinate on skeletal muscle fiber‐type remodeling are mediated by SUNCR1 and its downstream calcium/NFAT signaling pathway. In summary, our results demonstrate succinate induces transition of skeletal muscle fiber via SUNCR1 signaling pathway. These findings suggest the potential beneficial use of succinate‐based compounds in both athletic and sedentary populations.

PPAR expression, muscle size and metabolic rates across the gray catbird's annual cycle are greatest in preparation for fall migration.

Phenotypic flexibility across the annual cycle allows birds to adjust to fluctuating ecological demands. Varying energetic demands associated with time of year have been demonstrated to drive metabolic and muscle plasticity in birds, but it remains unclear what molecular mechanisms control this flexibility. We sampled gray catbirds at five stages across their annual cycle: tropical overwintering (January), northward spring (late) migration (early May), breeding (mid June), the fall pre-migratory period (early August) and southward fall (early) migration (end September). Across the catbird's annual cycle, cold-induced metabolic rate (V̇O2summit) was highest during migration and lowest during tropical wintering. Flight muscles exhibited significant hypertrophy and/or hyperplasia during fall migratory periods compared with breeding and the fall pre-migratory period. Changes in heart mass were driven by the tropical wintering stage, when heart mass was lowest. Mitochondrial content of the heart and pectoralis remained constant across the annual cycle as quantified by aerobic enzyme activities (CS, CCO), as did lipid catabolic capacity (HOAD). In the pectoralis, transcription factors PPARα, PPARδ and ERRβ, coactivators PGC-1α and β, and genes encoding proteins associated with fat uptake (FABPpm, Plin3) were unexpectedly upregulated in the tropical wintering stage, whereas those involved in fatty acid oxidation (ATGL, LPL, MCAD) were downregulated, suggesting a preference for fat storage over utilization. Transcription factors and coactivators were synchronously upregulated during pre-migration and fall migration periods in the pectoralis but not the heart, suggesting that these pathways are important in preparation for and during early migration to initiate changes to phenotypes that facilitate long-distance migration.

LABORATORY CRITERIA OF PERINATAL DAMAGE OF CENTRAL NERVOUS SYSTEM AT PREMATURE NEWBORNS

Fetal and neonatal hypoxia takes a special place among the damaging factors of central nervous system (CNS). All forms of oxygen deficiency are accompanied by the development of bioenergetic hypoxia, which leads to tension of metabolic processes of the organism. Metabolic effect of hypoxia includes stark reduce of mitochondrial activity due to a significant inhibition enzymes of the Krebs cycle: succinate dehydrogenase (SDH) and lactate dehydrogenase (LDH). In newborn babies is not always possible to objectively assess the condition of the CNS defeat, because very often the severity of lesions does not correspond to clinical symptoms, especially in premature newborns. So far determination the severity of hypoxic-ischemic CNS lesions is still very actual in modern medicine. More objective method of such an assessment is determine the activity of neurospecific enolase (NSE). The aim of the paper is to increase the efficiency of diagnosis of hypoxic CNS lesions in premature infants by determining the activity of NSE and study energy supply during the neonatal period. The concentration of NSE, SDH and LDH were determined in 15 conventionally healthy preterm infants (CHPI), which made the comparison group, and 64 premature babies with hypoxic-ischemic CNS lesions, which were divided into three groups: I group – 26 premature children with mild CNS lesions; II group – 20 premature children with severe hypoxic lesions and low birth weight; III group – 18 premature newborns with severe damage of central nervous system and extremely low birth weight. NSE activity was determined by enzyme immunoassay using reagents of the company «Fujirebio» (Sweden) on an automatic analyzer «Multiscan Plus» company «Labsystems» (Finland). Material for investigation was peripheral venous blood of newborns, which collected by vein punction at morning on an empty stomach. Metabolic effect of hypoxia in premature infants manifested by severe inhibition of mitochondrial respiratory activity, which appears in the reduction of aerobic enzyme activity of SDH and activation serum LDH. During the neonatal period in infants with perinatal hypoxic- ischemic lesions of the CNS levels of the of NSE, SDH and LDG aren’t normalized, that indicated on energy deficiency and requires the development of effective methods of correcting this condition. Perinatal hypoxia in premature neonates causes significant alteration of neuronal membranes and increase concentration in blood such neurospecific protein as NSE, whose concentration correlates with the degree of severity of CNS injury.

Aerobic and anaerobic enzyme activity in the hake Merluccius gayi gayi related to the Oxygen Minimum Zone off central-southern Chile

El Sistema de Corrientes de Humboldt de la costa de Chile posee una Zona de Minimo Oxigeno (ZMO) entre 30 y 250 m de profundidad, con concentraciones de oxigeno < 0,5 ml L-1. Las mayores densidades de merluza Merluccius gayi gayi se asocian a esta zona, sugiriendo que posee adaptaciones metabolicas para permanecer en ella. Se estimo el potencial aerobico y anaerobico de esta especie demersal mediante la medicion de enzimas metabolicas claves y del sistema de transporte de electrones (ETS) en diferentes tejidos (musculo blanco, corazon, cerebro e higado). La actividad de la enzima citrato sintasa (CS) y de la ETS fueron mayores en el cerebro y corazon, confirmando la predominancia del metabolismo aerobico en los organos vitales diferentes al musculo. La actividad promedio de la enzima anaerobica lactato deshidrogenasa (LDH) fluctuo entre 55 ± 17,5 and 263 ± 79 UI g-1 ww, siendo menor en el corazon y cerebro. Esta baja actividad de LDH y una alta razon MDH/LDH en estos organos vitales indican que ambos serian capaces de lidiar con periodos de acidificacion metabolica producida por hipoxia ambiental. Los niveles de LDH fueron excepcionalmente altos en el higado, lo que podria relacionarse con factores ambientales como la contaminacion ambiental. La baja razon MDH/LDH y la menor actividad de CS y ETS en el musculo, sumado a la alta actividad de LDH en el higado indicarian un perfil metabolico de M. gayi gayi para tolerar condiciones de hipoxia y por lo tanto permanecer en la ZMO, pero disminuyendo su actividad natatoria.

Phenotypic flexibility of thermogenesis in the hwamei (Garrulax canorus): responses to cold acclimation.

Cold acclimation in birds involves a comprehensive array of physiological and morphological adjustment ranging from changes in aerobic enzyme activity to metabolic rate and organ mass. In the present study, we investigated phenotypic variation in thermogenic activity in the hwamei (Garrulax canorus) under normal (35°C) or cold (15°C) ambient temperature conditions. Acclimation to an ambient temperature of 15°C for 4 wk significantly increased the body mass, basal metabolic rate (BMR), and energy intake, including both gross energy intake and digestible energy intake, compared with birds kept at 35°C. Furthermore, birds acclimated to 15°C increased the dry mass of their liver and kidneys, but not their heart and pectoral muscles, and displayed higher state-4 respiration in the liver, kidneys, heart, and pectoral muscles, and higher cytochrome-c oxidase (COX) activity in liver, kidney, and pectoral muscle, compared with those kept at 35°C. There was a positive correlation between BMR and state-4 respiration in all of the above organs except the liver, and between BMR and COX activity in all of the above organs. Taken together, these data illustrate the morphological, physiological, and enzymatic changes associated with cold acclimation, and support the notion that the hwamei is a bird species from temperate climates that exhibits high phenotypic flexibility of thermogenic capacity.

Scaling matters: incorporating body composition into Weddell seal seasonal oxygen store comparisons reveals maintenance of aerobic capacities

Adult Weddell seals (Leptonychotes weddellii) haul-out on the ice in October/November (austral spring) for the breeding season and reduce foraging activities for ~4 months until their molt in the austral fall (January/February). After these periods, animals are at their leanest and resume actively foraging for the austral winter. In mammals, decreased exercise and hypoxia exposure typically lead to decreased production of O2-carrying proteins and muscle wasting, while endurance training increases aerobic potential. To test whether similar effects were present in marine mammals, this study compared the physiology of 53 post-molt female Weddell seals in the austral fall to 47 pre-breeding females during the spring in McMurdo Sound, Antarctica. Once body mass and condition (lipid) were controlled for, there were no seasonal changes in total body oxygen (TBO2) stores. Within each season, hematocrit and hemoglobin values were negatively correlated with animal size, and larger animals had lower mass-specific TBO2 stores. But because larger seals had lower mass-specific metabolic rates, their calculated aerobic dive limit was similar to smaller seals. Indicators of muscular efficiency, myosin heavy chain composition, myoglobin concentrations, and aerobic enzyme activities (citrate synthase and β-hydroxyacyl CoA dehydrogenase) were likewise maintained across the year. The preservation of aerobic capacity is likely critical to foraging capabilities, so that following the molt Weddell seals can rapidly regain body mass at the start of winter foraging. In contrast, muscle lactate dehydrogenase activity, a marker of anaerobic metabolism, exhibited seasonal plasticity in this diving top predator and was lowest after the summer period of reduced activity.

Ocean acidification exerts negative effects during warming conditions in a developing Antarctic fish

Anthropogenic CO2 is rapidly causing oceans to become warmer and more acidic, challenging marine ectotherms to respond to simultaneous changes in their environment. While recent work has highlighted that marine fishes, particularly during early development, can be vulnerable to ocean acidification, we lack an understanding of how life-history strategies, ecosystems and concurrent ocean warming interplay with interspecific susceptibility. To address the effects of multiple ocean changes on cold-adapted, slowly developing fishes, we investigated the interactive effects of elevated partial pressure of carbon dioxide (pCO2) and temperature on the embryonic physiology of an Antarctic dragonfish (Gymnodraco acuticeps), with protracted embryogenesis (∼10 months). Using an integrative, experimental approach, our research examined the impacts of near-future warming [-1 (ambient) and 2°C (+3°C)] and ocean acidification [420 (ambient), 650 (moderate) and 1000 μatm pCO2 (high)] on survival, development and metabolic processes over the course of 3 weeks in early development. In the presence of increased pCO2 alone, embryonic mortality did not increase, with greatest overall survival at the highest pCO2. Furthermore, embryos were significantly more likely to be at a later developmental stage at high pCO2 by 3 weeks relative to ambient pCO2. However, in combined warming and ocean acidification scenarios, dragonfish embryos experienced a dose-dependent, synergistic decrease in survival and developed more slowly. We also found significant interactions between temperature, pCO2 and time in aerobic enzyme activity (citrate synthase). Increased temperature alone increased whole-organism metabolic rate (O2 consumption) and developmental rate and slightly decreased osmolality at the cost of increased mortality. Our findings suggest that developing dragonfish are more sensitive to ocean warming and may experience negative physiological effects of ocean acidification only in the presence of an increased temperature. In addition to reduced hatching success, alterations in development and metabolism due to ocean warming and acidification could have negative ecological consequences owing to changes in phenology (i.e. early hatching) in the highly seasonal Antarctic ecosystem.

Individual Variation in Thermogenic Capacity Is Correlated with Flight Muscle Size but Not Cellular Metabolic Capacity in American Goldfinches (Spinus tristis)

Abstract Cold tolerance and overwinter survival are positively correlated with organismal thermogenic capacity (=summit metabolic rate [Msum]) in endotherms. Msum varies seasonally in small-bird populations and may be mechanistically associated with variation in flight muscle size or cellular metabolic capacity, but the relative roles of these traits as drivers of individual variation in thermogenic performance are poorly known. We measured flight muscle size by ultrasonography, pectoralis and supracoracoideus muscle masses, and muscular activities of key aerobic enzymes (citrate synthase, carnitine palmitoyl transferase, and β-hydroxyacyl-CoA dehydrogenase) and correlated these measurements with Msum for individual American goldfinches (Spinus tristis) to test the hypotheses that muscle size and/or cellular metabolic capacity serve as prominent drivers of individual variation in organismal metabolic capacity. Ultrasonographic flight muscle size was weakly positively correlated with Msum ([Formula: see text]). Both log10-transformed Msum and flight muscle mass were significantly correlated with log10 body mass, so we calculated allometric residuals for log Msum and for log flight muscle mass to test their correlation independent of body mass. Flight muscle mass residuals were significantly positively correlated with Msum residuals, and this correlation was primarily driven by variation in pectoralis muscle mass. In contrast, none of the mass-specific activities of any enzyme in any muscle were significantly correlated with Msum. These data suggest that flight muscle size, not cellular metabolic capacity, is the primary driver of individual variation in thermogenic performance in goldfinches. This is consistent with the idea that phenotypic flexibility of flight muscle mass is a general mechanism mediating variation in metabolic performance in response to changing energy demands in birds.

Pathophysiology of muscle dysfunction in COPD

Muscle dysfunction often occurs in patients with chronic obstructive pulmonary disease (COPD) and may involve both respiratory and locomotor (peripheral) muscles. The loss of strength and/or endurance in the former can lead to ventilatory insufficiency, whereas in the latter it limits exercise capacity and activities of daily life. Muscle dysfunction is the consequence of complex interactions between local and systemic factors, frequently coexisting in COPD patients. Pulmonary hyperinflation along with the increase in work of breathing that occur in COPD appear as the main contributing factors to respiratory muscle dysfunction. By contrast, deconditioning seems to play a key role in peripheral muscle dysfunction. However, additional systemic factors, including tobacco smoking, systemic inflammation, exercise, exacerbations, nutritional and gas exchange abnormalities, anabolic insufficiency, comorbidities and drugs, can also influence the function of both respiratory and peripheral muscles, by inducing modifications in their local microenvironment. Under all these circumstances, protein metabolism imbalance, oxidative stress, inflammatory events, as well as muscle injury may occur, determining the final structure and modulating the function of different muscle groups. Respiratory muscles show signs of injury as well as an increase in several elements involved in aerobic metabolism (proportion of type I fibers, capillary density, and aerobic enzyme activity) whereas limb muscles exhibit a loss of the same elements, injury, and a reduction in fiber size. In the present review we examine the current state of the art of the pathophysiology of muscle dysfunction in COPD.

Phenotypic flexibility in passerine birds: Seasonal variation of aerobic enzyme activities in skeletal muscle

Improved winter cold tolerance is widespread among small passerines resident in cold climates and is generally associated with elevated summit metabolic rate ( M sum =maximum thermoregulatory metabolic rate) and improved shivering endurance with increased reliance on lipids as fuel. Elevated M sum and improved cold tolerance may result from greater metabolic intensity, due to mass-specific increase in oxidative enzyme capacity, or increase in the masses of thermogenic tissues. To examine the mechanisms underlying winter increases in M sum , we investigated seasonal changes in mass-specific and total activities of the key aerobic enzymes citrate synthase (CS) and β-hydroxyacyl CoA-dehydrogenase (HOAD) in pectoralis, supracoracoideus and mixed leg muscles of three resident passerine species, black-capped chickadee ( Poecile atricapillus), house sparrow ( Passer domesticus), and white-breasted nuthatch ( Sitta carolinensis). Activities of CS were generally higher in winter than in summer muscles for chickadees and house sparrows, but not nuthatches. Mass-specific HOAD activity was significantly elevated in winter relative to summer in all muscles for chickadees, but did not vary significantly with season for sparrows or nuthatches, except for sparrow leg muscle. These results suggest that modulation of substrate flux and cellular aerobic capacity in muscle contribute to seasonal metabolic flexibility in some species and tissues, but such changes play varying roles among small passerines resident in cold climates.

Evaluation of kinetic parameters and mass transfer of glucose-fed granules under hypoxic conditions

This study demonstrated that the availability of oxygen influenc the kinetic parameters of sludge granules for the utilization and mass transfer of substrates. Batch experiments revealed that substrate utilization of the coupled sludge granules followed Monod’s kinetic model under hypoxic conditions and at initial substrate concentrations ranging from 1,350 to 4,456 mg/L. The corresponding kinetic coefficients of ks (maximum specific substrate glucose utilization rate), Ks (half saturation coefficient), and Y (growth yield) were 5.6 ∼ 7.8/day, 58 ∼ 64 mg/L, and 0.11 ∼ 0.17 mg of MLSS/mg of COD, respectively. Low dissolved oxygen content suppressed the activity of aerobic enzymes, which resulted in a ks value between those of aerobic granules and anaerobic granules. The maximum oxygen consumption rate (ko = 0.89/day) was relatively higher while the half-saturation constant (Ko = 1.71 mg/L) was significantly lower than those of aerobic granules. These results imply that dissolved oxygen was used more efficiently under hypoxic conditions. Thiele modulus (ϕ) and effectiveness factor (η) analysis revealed that the activity of microorganisms inside the granules was limited by the availability of oxygen. These properties differed from those found in aerobic granules, anaerobic granules, and activated sludge.

The Effect of Oxygen on Anaerobic Color Removal of Azo Dye in a Sequencing Batch Reactor

AbstractIn this study, various amounts of oxygen were added to the anaerobic phase of an anaerobic‐aerobic sequencing batch reactor (SBR) receiving azo dye remazol brilliant violet 5R to mimic the input of oxygen into the anaerobic zones of biological textile wastewater treatment plants. The effect of oxygen on the anaerobic biodegradative capability of the mixed microbial culture for remazol brilliant violet 5R was investigated. To investigate the effect of oxygen on anaerobic azo dye biodegradation, the anaerobic phase of the SBR cultures were exposed to a very low limited amount of oxygen for various air flow rates. Initially, an air flow rate of 20 mL/min was applied, further on the air flow rate in the anaerobic phase was increased up to 40 mL/min. System performance was determined by monitoring chemical oxygen demand, color removal rate, activities of anaerobic (azo reductase) and aerobic enzymes (catechol 2,3‐dioxygenase, catechol 1,2‐dioxygenase). The results of percentage COD reduction at each stage were similar for all runs, giving an overall reduction of 96%. Anaerobic color removal efficiency and azo reductase activity of anaerobic microorganisms were adversely affected by the addition of oxygen. Color removal efficiencies of the anaerobic phases decreased from 80% down to 42 and 38% for the limited oxygen conditions of 20 mL/min and 40 mL/min, respectively. It was observed that the activity of catechol 2,3‐dioxygenase and catechol 1,2‐dioxygenase, involved in breakage of aromatic rings, increased after they are exposed to oxygen limited conditions compared to fully anaerobic conditions. It was also observed that catechol 1,2‐dioxygenase enzyme activity increased by increasing the oxygen level on oxygen limited conditions in the anaerobic zone.