Supply Of Metabolic Substrates Research Articles

The influence of carbon dioxide on cerebral metabolism and oxygen consumption: combining multimodal monitoring with dynamic systems modelling.

Hypercapnia increases cerebral blood flow. The effects on cerebral metabolism remain incompletely understood although studies show an oxidation of cytochrome c oxidase, Complex IV of the mitochondrial respiratory chain. Systems modelling was combined with previously published non-invasive measurements of cerebral tissue oxygenation, cerebral blood flow, and cytochrome c oxidase redox state to evaluate any metabolic effects of hypercapnia. Cerebral tissue oxygen saturation and cytochrome oxidase redox state were measured with broadband near infrared spectroscopy and cerebral blood flow velocity with transcranial Doppler ultrasound. Data collected during 5-min hypercapnia in awake human volunteers were analysed using a Fick model to determine changes in brain oxygen consumption and a mathematical model of cerebral hemodynamics and metabolism (BrainSignals) to inform on mechanisms. Either a decrease in metabolic substrate supply or an increase in metabolic demand modelled the cytochrome oxidation in hypercapnia. However, only the decrease in substrate supply explained both the enzyme redox state changes and the Fick-calculated drop in brain oxygen consumption. These modelled outputs are consistent with previous reports of CO2 inhibition of mitochondrial succinate dehydrogenase and isocitrate dehydrogenase. Hypercapnia may have physiologically significant effects suppressing oxidative metabolism in humans and perturbing mitochondrial signalling pathways in health and disease.

Ambient temperature, heat stress and fetal growth: A review of placenta-mediated mechanisms

Pregnancy is increasingly considered a period of vulnerability for extreme heat exposure. Multiple lines of evidence support that heat stress is associated with placental insufficiency, poor fetal growth and decreased birth weight. In this narrative review, we first summarize evidence linking ambient temperature or experimentally-induced heat stress with fetal and placental growth outcomes in humans, ruminants and murine species. We then synthesize the literature on putative underlying biological pathways with a focus on the placenta. Reviewed mechanisms include: reduced uterine-placental blood flow, impaired supply of metabolic substrates to the fetus, activation of the maternal stress-response system, and disruption of other endocrine and immune system endpoints. Taken together, this body of evidence supports that exposure to extreme ambient heat likely has adverse consequences for placental development and function. However, research investigating placenta-mediated pathophysiological mechanisms in humans remains extremely limited.

Trans-endothelial trafficking of metabolic substrates and its importance in cardio-metabolic disease

The endothelium acts as a gatekeeper, controlling the movement of biomolecules between the circulation and underlying tissues. Although conditions of metabolic stress are traditionally considered as causes of endothelial dysfunction, a principal driver of cardiovascular disease, accumulating evidence suggests that endothelial cells are also active players in maintaining local metabolic homeostasis, in part, through regulating the supply of metabolic substrates, including lipids and glucose, to energy-demanding organs. Therefore, endothelial dysfunction, in terms of altered trans-endothelial trafficking of these substrates, may in fact be an early contributor towards the establishment of metabolic dysfunction and subsequent cardiovascular disease. Understanding the molecular mechanisms that underpin substrate trafficking through the endothelium represents an important area within the vascular and metabolism fields that may offer an opportunity for identifying novel therapeutic targets. This mini-review summarises the emerging mechanisms regulating the trafficking of lipids and glucose through the endothelial barrier and how this may impact on the development of cardio-metabolic disease.

Arterial Oxygenation in Traumatic Brain Injury-Relation to Cerebral Energy Metabolism, Autoregulation, and Clinical Outcome.

Background:Ischemic and hypoxic secondary brain insults are common and detrimental in traumatic brain injury (TBI). Treatment aims to maintain an adequate cerebral blood flow with sufficient arterial oxygen content. It has been suggested that arterial hyperoxia may be beneficial to the injured brain to compensate for cerebral ischemia, overcome diffusion barriers, and improve mitochondrial function. In this study, we investigated the relation between arterial oxygen levels and cerebral energy metabolism, pressure autoregulation, and clinical outcome.Methods:This retrospective study was based on 115 patients with severe TBI treated in the neurointensive care unit, Uppsala university hospital, Sweden, 2008 to 2018. Data from cerebral microdialysis (MD), arterial blood gases, hemodynamics, and intracranial pressure were analyzed the first 10 days post-injury. The first day post-injury was studied in particular.Results:Arterial oxygen levels were higher and with greater variability on the first day post-injury, whereas it was more stable the following 9 days. Normal-to-high mean pO2 was significantly associated with better pressure autoregulation/lower pressure reactivity index (P = .02) and lower cerebral MD-lactate (P = .04) on day 1. Patients with limited cerebral energy metabolic substrate supply (MD-pyruvate below 120 µM) and metabolic disturbances with MD-lactate-/pyruvate ratio (LPR) above 25 had significantly lower arterial oxygen levels than those with limited MD-pyruvate supply and normal MD-LPR (P = .001) this day. Arterial oxygenation was not associated with clinical outcome.Conclusions:Maintaining a pO2 above 12 kPa and higher may improve oxidative cerebral energy metabolism and pressure autoregulation, particularly in cases of limited energy substrate supply in the early phase of TBI. Evaluating the cerebral energy metabolic profile could yield a better patient selection for hyperoxic treatment in future trials.

The Aerodynamics and Power Requirements of Forward Flapping Flight in the Mango Stem Borer Beetle (Batocera rufomaculata).

The need for long dispersal flights can drive selection for behavioral, physiological, and biomechanical mechanisms to reduce the energy spent flying. However, some energy loss during the transfer of momentum from the wing to the fluid is inevitable, and inherent to the fluid-wing interaction. Here, we analyzed these losses during the forward flight of the mango stem borer (Batocera rufomaculata). This relatively large beetle can disperse substantial distances in search of new host trees, and laboratory experiments have demonstrated continuous tethered flights that can last for up to an hour. We flew the beetles tethered in a wind tunnel and used high-speed videography to estimate the aerodynamic power from their flapping kinematics and particle image velocimetry (PIV) to evaluate drag and kinetic energy from their unsteady wakes. To account for tethering effects, we measured the forces applied by the beetles on the tether arm holding them in place. The drag of the flying beetle over the flapping cycle, estimated from the flow fields in the unsteady wake, showed good agreement with direct measurement of mean horizontal force. Both measurements showed that total drag during flight is ∼5-fold higher than the parasite drag on the body. The aerodynamic power estimated from both the motion of the wings, using a quasi-steady blade-element model, and the kinetic energy in the wake, gave mean values of flight-muscle mass-specific power of 87 and 65 W kg muscle-1, respectively. A comparison of the two values suggests that ∼25% of the energy is lost within the fluid due to turbulence and heat. The muscle mass-specific power found here is low relative to the maximal power output reported for insect flight muscles. This can be attributed to reduce weight support during tethered flight or to operation at submaximal output that may ensure a supply of metabolic substrates to the flight muscles, thus delaying their fatigue during long-distance flights.

Engineering Pseudomonas putida for isoprenoid production by manipulating endogenous and shunt pathways supplying precursors

BackgroundThe soil bacterium Pseudomonas putida is a promising platform for the production of industrially valuable natural compounds. In the case of isoprenoids, the availability of biosynthetic precursors is a major limiting factor. In P. putida and most other bacteria, these precursors are produced from pyruvate and glyceraldehyde 3-phosphate by the methylerythritol 4-phosphate (MEP) pathway, whereas other bacteria synthesize the same precursors from acetyl-CoA using the unrelated mevalonate (MVA) pathway.ResultsHere we explored different strategies to increase the supply of isoprenoid precursors in P. putida cells using lycopene as a read-out. Because we were not aiming at producing high isoprenoid titers but were primarily interested in finding ways to enhance the metabolic flux to isoprenoids, we engineered the well-characterized P. putida strain KT2440 to produce low but detectable levels of lycopene under conditions in which MEP pathway steps were not saturated. Then, we compared lycopene production in cells expressing the Myxococcus xanthus MVA pathway genes or endogenous MEP pathway genes (dxs, dxr, idi) under the control of IPTG-induced and stress-regulated promoters. We also tested a shunt pathway producing isoprenoid precursors from ribulose 5-phosphate using a mutant version of the Escherichia coli ribB gene.ConclusionsThe most successful combination led to a 50-fold increase in lycopene levels, indicating that P. putida can be successfully engineered to substantially increase the supply of metabolic substrates for the production of industrially valuable isoprenoids.

Abstract 277: Neonatal Cardiomyocyte-Released Signaling Protein Reduces Adipocyte Differentiation

The heart continuously cycles through periods of muscle contraction and relaxation to pump blood throughout the body, which requires a constant supply of metabolic substrates to the heart to power these contractile cycles. To ensure adequate energy availability, the heart must communicate with other organ systems to maintain global metabolic energy homeostasis. In addition to the role of the sympathetic nervous system in global metabolic regulation, mounting evidence suggests cardiomyocytes can release signaling factors that alter global energy balance through communication with other organ systems, including the liver and adipose tissue. To identify potential cardiomyocyte-released circulating factors, we collected media conditioned by neonatal rat ventricular myocytes (NRVM-CM) and screened for released-factor activity using an in vitro adipocyte differentiation assay. Treatment of differentiating 3T3-L1 adipocytes reduced lipid accumulation and decreased expression of adipocyte proteins, demonstrating NRVM-released factor activity. Released factor activity was also under the control of regulators of GPCR signaling as overexpression of G-protein coupled receptor kinase 2 (GRK2) further enhanced the NRVM-released factor activity. We further determined that NRVM released-factor activity was abolished by trypsin treatment and could be segregated into >30kDa CM fractions using centrifugal filter units. To identify proteins responsible for the NRVM-released factor activity, NRVM-CM retained in the 30kDA centrifugal filter units (containing all proteins >30kDa) was analyzed by mass spectrometry. This revealed a number of signaling proteins with known adipocyte regulatory roles that could potentially regulate adipocyte physiology. We confirmed these results by examining NRVM cell lysate and concentrated NRVM-CM by Western blot to test for the presence of decorin, one of the proteins identified by mass spectrometry known to have adipocyte regulatory roles. These results provide a framework to identify potential in vivo cardiomyocyte-released factors that regulate global energy balance.

Multiphoton Imaging Reveals Differences in Metabolic Auto‐fluorescence Signals Between Early and Late Proximal Tubule Segments of the Kidney

The kidney emits a large amount of auto‐fluorescence due to the existence of endogenous fluorophores. These include NAD(P)H and flavoproteins (such as FAD), important mitochondrial redox co‐factors essential for metabolic processes such as the citric acid cycle (TCA), beta oxidation and the electron transport chain (ETC). Imaging of metabolic auto‐fluorescence signals could therefore provide new insights into kidney physiology.Multiphoton microscopy (MP) is a powerful tool with high penetrance and reduced phototoxicity that can be used to image dynamic changes in cell structure and function in living tissue. We have used this approach to investigate auto‐fluorescence signals in proximal tubules (PTs) as readouts of cellular metabolism using freshly prepared murine kidney cortical slices. The peak emission of NAD(P)H (excited at 720 nm) was at 460 nm, as previously reported, whereas the peak emission of FAD (excited at 900 nm) was in the range of 560–610 nm, slightly red shifted compared to previous studies using single photon excitation. NAD(P)H signal showed expected changes in intensity in response to inhibition or uncoupling of the ETC. In contrast, no such changes were observed in FAD signal, suggesting that it is not redox sensitive. Striking differences in baseline NAD(P)H and FAD signals were observed between early (S1) and later (S2) sections of the PT, implying metabolic differences between these segments. These differences were also observed in intact kidneys using intravital microscopy, suggesting they are not artefacts of the slicing process.To further investigate these findings, we assessed how NAD(P)H and FAD signals change in real time in response to different single substrates metabolized by the PT. NAD(P)H was increased in both PT segments by lactate and the short chain fatty acid (FA) hexonate, and decreased in response to gutamine. FAD signal was also decreased by glutamine, but was increased by the long chain FA palmitate. Fluorescence lifetime microscopy (FLIM) of the NAD(P)H signal revealed 2 principal lifetimes, most likely corresponding to free and bound forms of the molecule. A single lifetime was identified for mitochondrial FAD in both PT segments, implying that differences in intensity are likely to be explained by differences in abundance of the same metabolite.In summary, using MP and FLIM we found that there are striking previously unknown differences in baseline mitochondrial auto‐fluorescence signals between S1 and S2 PT segments, implying underlying differences in metabolism. Moreover, the intensity of signals is dependent not only on mitochondrial redox state, but also on metabolic substrate supply. These findings may help to explain axial patterns of injury typically observed in certain kidney diseases.Support or Funding InformationJRM is a IKPP2 fellow funded by the European Union's Seventh Framework Programme for research, technological development and demonstration under the grant agreement no 608847This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Effect of temperature on FAD and NADH-derived signals and neurometabolic coupling in the mouse auditory and motor cortex.

Tight coupling of neuronal metabolism to synaptic activity is critical to ensure that the supply of metabolic substrates meets the demands of neuronal signaling. Given the impact of temperature on metabolism, and the wide fluctuations of brain temperature observed during clinical hypothermia, we examined the effect of temperature on neurometabolic coupling. Intrinsic fluorescence signals of the oxidized form of flavin adenine dinucleotide (FAD) and the reduced form of nicotinamide adenine dinucleotide (NADH), and their ratios, were measured to assess neural metabolic state and local field potentials were recorded to measure synaptic activity in the mouse brain. Brain slice preparations were used to remove the potential impacts of blood flow. Tight coupling between metabolic signals and local field potential amplitudes was observed at a range of temperatures below 29°C. However, above 29°C, the metabolic and synaptic signatures diverged such that FAD signals were diminished, but local field potentials retained their amplitude. It was also observed that the declines in the FAD signals seen at high temperatures (and hence the decoupling between synaptic and metabolic events) are driven by low FAD availability at high temperatures. These data suggest that neurometabolic coupling, thought to be critical for ensuring the metabolic health of the brain, may show temperature dependence, and is related to temperature-dependent changes in FAD supplies.

Autophagy provides metabolic substrates to maintain energy charge and nucleotide pools in Ras-driven lung cancer cells.

Autophagy degrades and is thought to recycle proteins, other macromolecules, and organelles. In genetically engineered mouse models (GEMMs) for Kras-driven lung cancer, autophagy prevents the accumulation of defective mitochondria and promotes malignancy. Autophagy-deficient tumor-derived cell lines are respiration-impaired and starvation-sensitive. However, to what extent their sensitivity to starvation arises from defective mitochondria or an impaired supply of metabolic substrates remains unclear. Here, we sequenced the mitochondrial genomes of wild-type or autophagy-deficient (Atg7(-/-)) Kras-driven lung tumors. Although Atg7 deletion resulted in increased mitochondrial mutations, there were too few nonsynonymous mutations to cause generalized mitochondrial dysfunction. In contrast, pulse-chase studies with isotope-labeled nutrients revealed impaired mitochondrial substrate supply during starvation of the autophagy-deficient cells. This was associated with increased reactive oxygen species (ROS), lower energy charge, and a dramatic drop in total nucleotide pools. While starvation survival of the autophagy-deficient cells was not rescued by the general antioxidant N-acetyl-cysteine, it was fully rescued by glutamine or glutamate (both amino acids that feed the TCA cycle and nucleotide synthesis) or nucleosides. Thus, maintenance of nucleotide pools is a critical challenge for starving Kras-driven tumor cells. By providing bioenergetic and biosynthetic substrates, autophagy supports nucleotide pools and thereby starvation survival.

Editorial: "Transcellular Cycles Underlying Neurotransmission".

Neuronal action potentials and neurotransmitter releases induce important alterations in the extracellular millieu, including increased K+ concentrations from membrane repolarization and increased neurotransmitter levels from trans-synaptic signaling (1, 2). It becomes crucial then to remove, fast and efficiently, these ionic and neurotransmitter surges and to prepare the synapsis for a new neurotransmission event (3). In parallel, the energy demands of these metabolic movements must be fulfilled from substrates, such as glucose and lactate, obtained from cerebrovascular supplies (4, 5). Surrounding astrocytes coordinate all these tasks, playing a central role during neurotransmission, many times operating intercellularly as astrocytic networks (6, 7). Summarizing, the adequate operation of neurotransmission requires the transcellular coupling of neuronal and astrocytic metabolisms to a suitable supply of metabolic substrates from the microvasculature. Pathological alterations in these processes underlie the most morbid and prevalent neurological disorders, including ischemic or traumatic episodes and neurodegeneration. Despite enormous progress in our understanding of neurotransmission during the last decades, important questions remain insufficiently explored including the quantitative assessment of transcellular cycles of glutamate, glutamine, and GABA supporting glutamatergic or gabaergic neurotransmissions, the preferred metabolic substrates, as glucose and/or lactate, supporting the energy demands under resting or stimulated conditions, and the mechanisms underlying neurovascular coupling. In addition, the important question on how all these processes occur and integrate under the in vivo situation reaches, in this context, vital relevance. Recently, a variety of non-invasive approaches have allowed the investigation of these aspects in vivo (8), outstandingly, those involving functional magnetic resonance imaging and 13C magnetic resonance spectroscopy methods. The following e-book entitled “Transcellular Cycles Underlying Neurotransmission” provides an authoritative overview of these issues, compiling contributions from leading scientists in this field. In the study of neuroglial interactions in vivo, Rodrigues et al. (9) provide a convenient introduction to the fundamentals of 13C NMR spectroscopy and its applications to cerebral energy metabolism, Duarte et al. (10) report on the compartmentalized metabolism of (1,6-13C2) glucose in the brain in vivo, Shen (11) reviews the mathematical modeling strategies used to simulate quantitatively the operation glutamate–glutamine cycle in vivo, and Sampol et al. (12) address the metabolism of glucose and lactate in the stimulated, awake, rat brain. Similarly, Bartnick-Olson et al. (13) illustrate the use of 13C NMR to evaluate the altered neuroglial interactions in response to traumatic brain injury. The neurophysiological, metabolic, and cellular compartmentation events underlying functional neuroimaging by MRI are discussed by Moreno et al. (14), while Lizarbe et al. (15) cover the use of different MRI and MRS strategies to evaluate the ionic responses during hypothalamic activation by appetite stimulation. The role of astrocytic metabolic networks in metabolic coupling is discussed by Escartin and Rouach (16), whereas Bergessen and Gjedde (17) elaborate on the interesting hypothesis of lactate becoming a volume transmitter of metabolic states through the brain. In summary, this e-book provides a broad coverage of recent progress in neuroglial coupling mechanisms underlying neuronal firing under physiological or pathological situations and their integration within astrocytic networks and associated neurovascular responses, as observed by advanced magnetic resonance imaging and spectroscopy methods in vivo. We hope that this compilation becomes useful for a wide range of neuroscientists, from young students entering the field and looking for a global perspective, to established scientists, searching for specialized views on critical issues of cerebral neurotransmission in vivo.

Mathematical modelling of the diurnal regulation of the MEP pathway in Arabidopsis.

Isoprenoid molecules are essential elements of plant metabolism. Many important plant isoprenoids, such as chlorophylls, carotenoids, tocopherols, prenylated quinones and hormones are synthesised in chloroplasts via the 2-C-methyl-d-erythritol 4-phosphate (MEP) pathway. Here we develop a mathematical model of diurnal regulation of the MEP pathway in Arabidopsis thaliana. We used both experimental and theoretical approaches to integrate mechanisms potentially involved in the diurnal control of the pathway. Our data show that flux through the MEP pathway is accelerated in light due to the photosynthesis-dependent supply of metabolic substrates of the pathway and the transcriptional regulation of key biosynthetic genes by the circadian clock. We also demonstrate that feedback regulation of both the activity and the abundance of the first enzyme of the MEP pathway (1-deoxy-D-xylulose 5-phosphate synthase, DXS) by pathway products stabilizes the flux against changes in substrate supply and adjusts the flux according to product demand under normal growth conditions. These data illustrate the central relevance of photosynthesis, the circadian clock and feedback control of DXS for the diurnal regulation of the MEP pathway.

Nitrogen losses in anoxic marine sediments driven by Thioploca–anammox bacterial consortia

Ninety per cent of marine organic matter burial occurs in continental margin sediments, where a substantial fraction of organic carbon escapes oxidation and enters long-term geologic storage within sedimentary rocks. In such environments, microbial metabolism is limited by the diffusive supply of electron acceptors. One strategy to optimize energy yields in a resource-limited habitat is symbiotic metabolite exchange among microbial associations. Thermodynamic and geochemical considerations indicate that microbial co-metabolisms are likely to play a critical part in sedimentary organic carbon cycling. Yet only one association, between methanotrophic archaea and sulphate-reducing bacteria, has been demonstrated in marine sediments in situ, and little is known of the role of microbial symbiotic interactions in other sedimentary biogeochemical cycles. Here we report in situ molecular and incubation-based evidence for a novel symbiotic consortium between two chemolithotrophic bacteria--anaerobic ammonium-oxidizing (anammox) bacteria and the nitrate-sequestering sulphur-oxidizing Thioploca species--in anoxic sediments of the Soledad basin at the Mexican Pacific margin. A mass balance of benthic solute fluxes and the corresponding nitrogen isotope composition of nitrate and ammonium fluxes indicate that anammox bacteria rely on Thioploca species for the supply of metabolic substrates and account for about 57 ± 21 per cent of the total benthic N2 production. We show that Thioploca-anammox symbiosis intensifies benthic fixed nitrogen losses in anoxic sediments, bypassing diffusion-imposed limitations by efficiently coupling the carbon, nitrogen and sulphur cycles.

Actions and interactions of AMPK with insulin, the peroxisomal-proliferator activated receptors and sirtuins

AMP-activated protein kinase (AMPK) activity responds to a requirement to increase cellular ATP production and/or to conserve available ATP. AMPK is therefore central to the mechanisms of adjustment to fluctuating energy demand or metabolic substrate supply. AMPK has important actions in several insulin-responsive tissues, as well as in the pancreatic β cell, through which it can modulate glycemic control, insulin action and metabolic substrate selection and disposal. We review recent novel findings elucidating the mechanisms by which AMPK activation can correct impaired insulin action. However, we also emphasize not only the similarities, but also the differences in the actions of insulin and AMPK. We focus on metabolic interfaces between AMPK, peroxisomal proliferator-activated receptors, sirtuins and mTORC.

Seasonal Changes in Methanogenesis and Methanogenic Community in Three Peatlands, New York State

Fluctuating environmental conditions can promote diversity and control dominance in community composition. In addition to seasonal temperature and moisture changes, seasonal supply of metabolic substrates selects populations temporally. Here we demonstrate cascading effects in the supply of metabolic substrates on methanogenesis and community composition of anaerobic methanogenic archaea in three contrasting peatlands in upstate New York. Fresh samples of peat soils, collected about every 3 months for 20 months and incubated at 22 ± 2°C regardless of the in situ temperature, exhibited potential rates of methane (CH4) production of 0.02–0.2 mmol L−1 day−1 [380–3800 nmol g−1 (dry) day−1). The addition of acetate stimulated rates of CH4 production in a fen peatland soil, whereas addition of hydrogen (H2), and simultaneous inhibition of H2-consuming acetogenic bacteria with rifampicin, stimulated CH4 production in two acidic bog soils, especially, in autumn and winter. The methanogenic community structure was characterized using T-RFLP analyses of SSU rRNA genes. The E2 group of methanogens (Methanoregulaceae) dominated in the two acidic bog peatlands with relatively greater abundance in winter. In the fen peatland, the E1 group (Methanoregulaceae) and members of the Methanosaetaceae were co-dominant, with E1 having a high relative abundance in spring. Change in relative abundance profiles among methanogenic groups in response to added metabolic substrates was as predicted. The acetate-amendment increased abundance of Methanosarcinaceae, and H2-amendment enhanced abundance of E2 group in all peat soils studied, respectively. Additionally, addition of acetate increased abundance of Methanosaetaceae only in the bog soils. Variation in the supply of metabolic substrates helps explain the moderate diversity of methanogens in peatlands.

Deterioration of physical performance and cognitive function in rats with short‐term high‐fat feeding

Efficiency, defined as the amount of work produced for a given amount of oxygen consumed, is a key determinant of endurance capacity, and can be altered by metabolic substrate supply, in that fatty acid oxidation is less efficient than glucose oxidation. It is unclear, however, whether consumption of a high-fat diet would be detrimental or beneficial for endurance capacity, due to purported glycogen-sparing properties. In addition, a high-fat diet over several months leads to cognitive impairment. Here, we tested the hypothesis that short-term ingestion of a high-fat diet (55% kcal from fat) would impair exercise capacity and cognitive function in rats, compared with a control chow diet (7.5% kcal from fat) via mitochondrial uncoupling and energy deprivation. We found that rats ran 35% less far on a treadmill and showed cognitive impairment in a maze test with 9 d of high-fat feeding, with respiratory uncoupling in skeletal muscle mitochondria, associated with increased uncoupling protein (UCP3) levels. Our results suggest that high-fat feeding, even over short periods of time, alters skeletal muscle UCP3 expression, affecting energy production and physical performance. Optimization of nutrition to maximize the efficiency of mitochondrial ATP production could improve energetics in athletes and patients with metabolic abnormalities.

Preeclampsia: Exposing Future Cardiovascular Risk in Mothers and Their Children

There is an increased risk for future cardiovascular disease in women who have had preeclampsia. In infants born to mothers with preeclampsia, there is growing evidence of increased risk for both cardiovascular disease and preeclampsia. Epidemiologic and experimental data provide a strong link between intrauterine exposure to preeclampsia and subsequent risk for the development of cardiovascular disease in women.

Glucose transport in the heart.

The heart is a unique organ in many ways. It consists of specialized muscle cells (cardiomyocytes), which are adapted to contract constantly in a coordinated fashion. This is vital to the survival of the organism given the central role of the heart in the maintenance of the cardiovascular system that delivers oxygen, metabolic substrates and hormones to the rest of the body. In order for the heart to maintain its function it must receive a constant supply of metabolic substrates, to generate ATP to maintain contractile function, without fatigue. Thus the heart is capable of utilizing a variety of metabolic substrates and is able to rapidly adapt its substrate utilization in the face of changes in substrate supply. The major metabolic substrate for the heart is fatty acids. However, up to 30% of myocardial ATP is generated by glucose and lactate, with smaller contributions from ketones and amino acids. Although glucose is not the major metabolic substrate in the heart at rest, there are many circumstances in which it assumes greater importance such as during ischemia, increased workload and pressure overload hypertrophy. Like all other cells, glucose is transported into cardiac myocytes by members of the family of facilitative glucose transporters (GLUTs). In this regard, cardiomyocytes bear many similarities to skeletal muscle, but there are also important differences. For example, the most abundant glucose transporter in the heart is the GLUT4 transporter, in which translocation to the plasma membrane represents an important mechanism by which the net flux of glucose into the cell is regulated. Because cardiomyocytes are constantly contracting it is likely that contraction mediated GLUT4 translocation represents an important mechanism that governs the entry of glucose into the heart. While this is also true in skeletal muscle, because many muscles are often at rest, insulin mediated GLUT4 translocation represents a quantitatively more important mechanism regulating skeletal muscle glucose uptake than is the case in the heart. In contrast to skeletal muscle, where most GLUT1 is in perineural sheaths (1), in the heart there is significant expression of GLUT1 (2), which under certain circumstances is responsible for a significant component of basal cardiac glucose uptake. This review will summarize the current state of knowledge regarding the regulation of glucose transporter expression, and the regulation of glucose transport into myocardial cells.

Ventricular septal defect closure in a neonate with combined methylmalonic aciduria/homocystinuria

Methylmalonic acidemia with associated homocystinuria is a rare inborn error of amino acid metabolism affecting energy supply on the cellular level. Its effects on recovery from surgically induced organ ischemia are largely unknown. We report the successful closure of a nonrestrictive ventricular septal defect by following a normothermic strategy combined with ample metabolic substrate supply.

Partial recovery of in vivo function by improved incubation conditions of isolated renal proximal tubule. II. Change of Na-HCO3 cotransport stoichiometry and of response to acetazolamide.

In the preceding publication we reported that some transport properties of proximal tubules perfused in vitro differ from those of tubules perfused in vivo, and that the in vivo function can be largely recuperated by improved metabolic substrate supply and stimulation with norepinephrine (NE). Since we have previously observed that the basolateral Na-HCO3-cotransporter operates with an overall stoichiometric ratio of q approximately 3 HCO3- :1 Na+ in vivo, but with q approximately 2 HCO3- :1 Na+ in vitro and that it responds differently in both cases to acetazolamide (ACZ), we have now tested whether the cotransporter can regain its in vivo function in vitro if the incubation conditions are improved. Cell membrane potentials (Vb) and cell pH (pHi) were measured with microelectrodes and microfluorimetric techniques on isolated S2 segments of rabbit proximal tubule and the instantaneous Vb response to a 2:1 reduction of bath HCO3- or Na+ concentration was determined. (DeltaVb)HCO3 and (deltaVb)Na averaged 13.1 +/- 0.9 mV (SEM) and 6.9 +/- 0.5 mV in D-glucose-containing control HCO3-Ringer solution and decreased respectively to 10.1 +/- 0.5 mV and 3.8 +/- 0.2 mV (n = 8) after incubation in tissue culture medium and NE (10(-5) mmol/l). These data imply that q increased from 1.9 to 2.7. Concomitantly the tubules became susceptible to ACZ (1 mmol/l), which reduced (deltaVb)HCO3 in control conditions only to 94.6 +/- 1.2% but under improved incubation conditions to 64.5 +/- 2.4%. As verified in voltage divider measurements the latter reduction was not caused by activation of a basolateral K+ conductance. The results indicate that improved incubation conditions can at least partially revert cotransport function towards that of the in vivo state. The effect of ACZ may be explained if in the improved state 1 CO32- + 1 HCO3- + 1 Na+ are cotransported, in which case inhibition of carbonic anhydrase (CA) may cause a CO32-/pH disequilibrium to develop in the basal labyrinth which impedes the cotransport. Under conventional incubation conditions, however, when only 2 HCO3- + 1 Na+ are cotransported no such disequilibrium should develop irrespective of whether CA is active or inhibited.