Distinct Glycolysis Inhibitors Determine Retinal Cell Sensitivity to Glutamate-Mediated Injury

In this study, we analyzed how distinct glycolysis inhibitors influenced the redox status of retinal cells, used as a neuronal model. Three different approaches were used to inhibit glycolysis: the cells were submitted to iodoacetic acid (IAA), an inhibitor of glyceraldehyde 3-phosphate dehydrogenase, to 2-deoxy-glucose (DG) in glucose-free medium, which was used as a substitute of glucose, or in the absence of glucose. The redox status of the cells was evaluated by determining the reduction of MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide). By the analysis of dose-response curves of MTT reduction, IAA showed values of IC₅₀ = 7.02 × 10^–5 M, whereas DG showed values of IC₅₀ = 7.42 × 10^–4 M. Upon 30 min-incubation, glucose deprivation, per se, did not significantly affect MTT reduction. We also evaluated the reduction of MTT as an indicator of cell injury by exposing the cells to 100 M glutamate during the decrement of glycolysis function. In the presence of glutamate, for 2 h, there was a decrease in MTT reduction, which was potentiated in the presence of DG (10-20% decrease), in the presence of IAA (about 30% decrease) or in glucose-free medium (about 30% decrease). Major changes observed by the MTT assay, upon exposure to glutamate, indicative of changes in the redox status of retinal cells, were concomitant with variations in intracellular ATP. Under glucose deprivation, endogenous ATP decreased significantly from 38.9 ± 4.4 to 13.3 ± 0.7 nmol/mg protein after exposure to 100 M glutamate. The results support a different vulnerability of retinal cells after being exposed to distinct forms of glycolysis inhibition.     

Activation of p38 MAPK and increased glucose transport in chronic hibernating swine myocardium

In preconditioned myocardium, activation of the mitogen-activated protein kinase (MAPK) p38 leads to increased glucose uptake via enhanced GLUT-4 translocation. Glucose uptake is also increased in chronic hibernating myocardium, but the role of p38 MAPK and GLUT-4 translocation has not been studied. Nine swine underwent instrumentation of the proximal left anterior descending coronary artery (LAD) with a small, external constrictor. At 3 mo after instrumentation, myocardial glucose uptake by PET imaging was higher in the LAD than in the remote region under basal, fasted conditions (0.08 +/- 0.02 vs. 0.04 +/- 0.01 micromol.min(-1).g(-1), P < 0.05). Compared with the remote region, the LAD region demonstrated increased membrane-bound GLUT-4 relative to total content (61 +/- 04 vs. 45 +/- 06%, P < 0.05), higher glycogen (28.37 +/- 4.41 vs. 19.26 +/- 1.87 mg/g wet wt, P < 0.05), and increased inducible nitric oxide synthase (NOS) activity (1.43 +/- 0.34 vs. 0.51 +/- 0.21 activity/mg protein, P < 0.05). p38 MAPK was 47 +/- 14% higher in the LAD than in the remote region (P < 0.05) and correlated well with the absolute degree of GLUT-4 membrane-bound translocation (r = 0.81, P < 0.01), relative increase in glycogen (r = 0.70, P < 0.05), and total NOS activity (r = 0.68, P < 0.05). In chronic hibernating myocardial tissue, p38 MAPK activation is increased under basal fasted conditions and correlates well with the increased degree of GLUT-4 translocation, glycogen accumulation, and NOS activity. As in preconditioned myocardium, activation of p38 MAPK may play an important role in the metabolic adaptations that characterize chronic hibernating myocardium.     

Effects of dinitrophenol and oligomycin on the coupling between anaerobic metabolism and anaerobic sodium transport by the isolated turtle bladder

Dinitrophenol (1 x 10^-5 M) has been found to inhibit anaerobic sodium transport by the isolated urinary bladder of the fresh water turtle. Concurrently, anaerobic glycolysis was stimulated markedly. However, tissue ATP levels diminished only modestly, remaining at approximately 75% of values observed under anaerobic conditions without DNP. The utilization of glucose (from endogenous glycogen) corresponded closely to that predicted from the molar quantities of lactate formed. Thus the glycolytic pathway was completed in the presence of DNP and if ATP were synthesized normally during glycolysis, synthesis should have been increased. On the other hand, the decrease in Na transport should have decreased ATP utilization. Oligomycin did not block sodium transport either aerobically or anaerobically, but ATP concentrations did decrease. When anaerobic glycolysis was blocked by iodoacetate, pyruvate did not sustain sodium transport thus suggesting that no electron acceptors were available in the system. Two explanations are entertained for the anaerobic effect of DNP: (a) Stimulation by DNP of plasma membrane as well as mitochondrial ATPase activity; (b) inhibition of a high energy intermediate derived from glycolytic ATP or from glycolysis per se. The arguments relevant to each possibility are presented in the text. Although definitive resolution is not possible, we believe that the data favor the hypothesis that there was a high energy intermediate in the anaerobic system and that this intermediate, rather than ATP, served as the immediate source of energy for the sodium pump.     

Effects of iloprost,a PGI2 derivative,on ischemic myocardial energy and carbohydrate metabolism in dogs

Effects of iloprost, which is a stable prostacyclin analogue, on the ischemic myocardium were examined in the open-chest dog heart, in terms of biochemical parameters. Ischemia was initiated by ligating the left anterior descending coronary artery. When the coronary artery was ligated for 3 min, the levels or glycogen, fructose-1,6-diphosphate (FDP), adenosine triphosphate and creatinephosphate decreased, and the levels of glucose-6-phosphate (G6P), fructose-6-phosphate (F6P), lactate, adenosine diphosphate and adenosine monophosphate increased. During ischemia, therefore, energy charge potential was significantly decreased from 0.89±0.01 to 0.82±0.01, and ([G6P]+[F6P])/[FDP] and [lactate]/[pyruvate] ratios were significantly increased from 1.75±0.30 to 29.05±5.70 and 13±3 to 393±112, respectively. Iloprost (0.1, 0.3, or 1 g·kg^–1) was injected intravenously 5 min before the onset of ischemia. Iloprost (0.1, 0.3, and 1 g·kg^–1) reduced the ischemia-induced decrease in energy charge potential to 94, 74, and 86%, respectively, the increase in ([G6P]+[F6P]/[FDP] to 38, 29, 32%, respectively, and the increase in [lactate]/[pyruvate] to 67, 45, 65%, respectively. These results suggest that iloprost lessens the myocardial metabolic derangements produced by ischemia, and the most potent effect was obtained at the dose of 0.3 g·kg^–1.     

Change in substrate metabolism in isolated mouse hearts following ischemia-reperfusion

Several genetic and transgenic mouse models are currently being used for studying the regulation of myocardial contractility under normal conditions and in disease states. Little information has been provided, however, about myocardial energy metabolism in mouse hearts. We measured glycolysis, glucose oxidation and palmitate oxidation (using ³H-glucose, ¹⁴C-glucose and ³H-palmitate) in isolated working mouse hearts during normoxic conditions (control group) and following a 15 min global no-flow ischemic period (reperfusion group). Fifty min following reperfusion (10 min Langendorff perfusion + 40 min working heart perfusion) aortic flow, coronary flow, cardiac output, peak systolic pressure and heart rate were 44 ± 4, 88 ± 4, 57 ± 4, 94 ± 2 and 81 ± 4% of pre-ischemic values. Rates of glycolysis and glucose oxidation in the reperfusion group (13.6 ± 0.8 and 2.8 ± 0.2 mol/min/g dry wt) were not different from the control group (12.3 ± 0.6 and 2.5 ± 0.2 mol/min/g dry wt). Palmitate oxidation, however, was markedly elevated in the reperfusion group as compared to the control group (576 ± 37 vs. 357 ± 21 nmol/min/g dry wt, p < 0.05). This change in myocardial substrate utilization was accompanied by a marked fall in cardiac efficiency measured as cardiac output/oxidative ATP production (136 ± 10 vs. 54 ± 5 ml/mol ATP, p < 0.05, control and reperfusion group, respectively). We conclude that ischemia-reperfusion in isolated working mouse hearts is associated with a shift in myocardial substrate utilization in favour of fatty acids, in line with previous observations in rat.     

Metabolic control analysis of anaerobic glycolysis in human hibernating myocardium replaces traditional concepts of flux control

Myocardial hibernation represents an adaptation to sustained ischemia to maintain tissue vitality during severe supply-demand imbalance which is characterized by an increased glucose uptake. To elucidate this adaptive protective mechanism, the regulation of anaerobic glycolysis was investigated using human biopsies. In hibernating myocardium showing an increase in anaerobic glycolytic flux metabolizing exogenous glucose, the adjustment of flux through this pathway was analyzed by flux:metabolite co-responses. By this means, a previously unknown pattern of regulation using multisite modulation was found which largely differs from traditional concepts of metabolic control of the Embden-Meyerhof pathway in normal and diseased myocardium.     

Reduced sarcoplasmic reticulum Ca2+-ATPase activity and dephosphorylated phospholamban contribute to contractile dysfunction in human hibernating myocardium

Human hibernating myocardium (HHM) is characterized by reversible contractile dysfunction during chronic ischemia. A disturbed calcium-homeostasis is a decisive factor for reduced functional capacity in heart diseases. We therefore investigated calcium-handling proteins in HHM. In 12 patients suffering from multi-vessel coronary artery disease and contractile dysfunction with indication for bypass surgery, HHM was detected preoperatively by thallium scintigraphy, radionuclide ventriculography and dobutamine echocardiography. Transmural biopsies of these regions were taken and analyzed by immunohistochemistry and electron microscopy. Furthermore, SR-calcium ATPase (SERCA2a), phospholamban (PLN), the phosphorylated forms of PLN (PLN-Ser16, PLN-Thr17) as well as sodium-calcium exchanger (NCX) and ryanodine receptor (RyR2) were investigated by RT-PCR and Western-blotting. Additionally, SERCA2a activity was measured by an enzyme-coupled assay. In all patients complete functional recovery could be documented 3 months after revascularization by repeating all preoperative investigations. In HHM maximal SERCA2a activity was significantly reduced (HHM: 424.5± 33.9, control: 609.0± 48.5 nmol ATP mg protein⁻¹ min⁻¹, p≤ 0.05), whereas SERCA2a protein levels were unchanged. mRNA levels (HHM: 1.36± 0.08 vs. control: 0.78± 0.04, p≤ 0.05) and protein amount (HHM:1.67± 0.14 vs. control: 1.00± 0.04, p≤ 0.05) of PLN (A1) were increased resulting in an increased PLN:SERCA2a-ratio. PLN-Ser16 (HHM: 0.60± 0.08 vs. control: 1.00± 0.11, p≤ 0.05) and PLN-Thr17 (HHM: 0.63± 0.11 vs. control: 1.00± 0.06, p≤ 0.05) phosphorylation was significantly decreased. RyR2 and NCX showed no significant alteration. In HHM a decreased activity of SERCA2a due to an impaired phosphorylation of PLN contributes to contractile dysfunction. The increase in the relative ratio of PLN/SERCA2a leads to a decreased calcium affinity of SERCA2a.     

Acidosis,glycolysis and energy state in anaerobic heart tissue from rainbow trout

With focus on metabolism not depending on contractility in myocardial tissue from rainbow trout, Oncorhynchus mykiss, the effects of high CO₂ on lactate production, phosphocreatine, creatine, ATP, ADP, AMP and intracellular pH were examined under a blockage of cell respiration either alone or in combination with a glycolytic inhibition. Irrespective of metabolic interventions, a change in CO₂ from 1 to either 11 or 5% of the gas mixture perfusing the muscle bath with 15 mmol·l^-1 HCO _- ³ caused a drop of intracellular pH from 7.4 to either 6.5 or 7.0, respectively. An elevation of CO₂ to 11% diminished the rate of anaerobic lactate formation and slightly lowered anaerobic energy degradation. The further addition of 1 mmol·l^-1 iodoacetate to inhibit glycolysis strongly enhanced the tendency of acidosis to lower energy degradation. Moreover, iodoacetate induced a parallel decrease in ATP and total concentration of phosphorylated adenylates and an increase in resting tension. These effects were all substantially dampened by acidosis and could not immediately be related to tissue content of energy-rich phosphates. Tentatively, the depression of resting tension was the prime effect and a cause of the other effects acidosis. However, these were not affected by an inhibition of resting tension development with 2,3-butadione monoxime. The results suggest that glycolysis protects the anaerobic myocardium also by means not immediately related to tissue energy state. Acidosis exerts a similar protection, which is marginal as long as glycolysis is fully active, but substantial with an inhibited glycolysis.Abbreviations Cr _t total tissue concentration of creatine - G _PCr energy liberated per mol PCr hydrolyzed - IAA iodoacetate - PCr phosphocreatine - PE total tissue concentration of energy-rich phosphate bonds - pH _i intracellular pH - P _i inorganic phosphate - TAN total tissue concentration of phosphorylated adenylates - 2,3-BDM 2,3-butadione monoxime - SE standard error of the mean     

Physiology of a colony of<Emphasis Type="Italic"> Pleurotus pulmonarius</Emphasis> grown on medium overlaid with a Cellophane membrane

The physiology of a colony of Pleurotus pulmonarius grown on potato dextrose agar overlaid with a Cellophane membrane (PDA-WC) was studied. On PDA-WC, the colony presented higher biomass density and productivity of fruit body formation (4.84±0.23 mg mycelial biomass/cm² and 23.7±3.12 g ml^–1 h^–1, respectively) than that which developed on potato dextrose agar without Cellophane (PDA-OC; 0.26±0.01 mg mycelial biomass/cm² and 10.8±1.57 g ml^–1 h^–1, respectively). In cultures developed on PDA-WC, intracellular laccases and -1,3-glucanases activities were lower [12±0.9 arbitrary units (AU)/g mycelial biomass and 1.33±0.1 international units (IU)/g mycelial biomass, respectively] than those observed on PDA-OC (20.65±1.0 AU/g mycelial biomass and 3.67±0.2 IU/g mycelial biomass, respectively). In cultures developed on PDA-WC, intracellular protein and glycogen concentrations were lower (1.9±0.9 and 117±3.5 mg/g mycelial biomass, respectively) than those observed on PDA-OC (14.3±1.1 and 347±2.9 mg/g mycelial biomass, respectively). The radial growth rate and the content of glucans in the cell wall were not significantly different between cultures developed on PDA-WC and PDA-OC. These results show that the use of the Cellophane as a tool to study in vitro fungal physiology might affect the interpretation of experimental results, since the physiology under otherwise similar conditions was different on medium with and without Cellophane.     

Influence of vanadate on glycolysis,intracellular sodium,and pH in perfused rat hearts

Vanadium compounds have been shown to cause a variety of biological and metabolic effects including inhibition of certain enzymes, alteration of contractile function, and as an insulin like regulator of glucose metabolism. However, the influence of vanadium on metabolic and ionic changes in hearts remains to be understood. In this study we have examined the influence of vanadate on glucose metabolism and sodium transport in isolated perfused rat hearts. Hearts were perfused with 10 mM glucose and varying vanadate concentrations (0.7100 M) while changes in high energy phosphates (ATP and phosphocreatine (PCr)), intracellular pH, and intracellular sodium were monitored using 31P and 23Na NMR spectroscopy. Tissue lactate, glycogen, and (Na+, K+)-ATPase activity were also measured using biochemical assays. Under baseline conditions, vanadate increased tissue glycogen levels two fold and reduced (Na+, K+)-ATPase activity. Significant decreases in ATP and PCr were observed in the presence of vanadate, with little change in intracellular pH. These changes under baseline conditions were less severe when the hearts were perfused with glucose, palmitate and b-hydroxybutyrate. During ischemia vanadate did not limit the rise in intracellular sodium, but slowed sodium recovery on reperfusion. The presence of vanadate during ischemia resulted in attenuation of acidosis, and reduced lactate accumulation. Reperfusion in the presence of vanadate resulted in a slower ATP recovery, while intracellular pH and PCr recovery was not affected. These results indicate that vanadate alters glucose utilization and (Na+, K+)-ATPase activity and thereby influences the response of the myocardium to an ischemic insult.     

Carbohydrate metabolism in several tissues of rainbow trout,Oncorhynchus mykiss,is modified during ovarian recrudescence

• 1.1. Several pathways of carbohydrate metabolism were evaluated in three different tissues—liver, gonad and kidney—of a hatchery-reared population of rainbow trout (Oncorhynchus mykiss) which characterised two different stages of their gonadal maturation, i.e. previtellogenesis and established exogenous vitellogenesis.
• 2.2. A fall in liver glycogen levels was observed during exogenous vitellogenesis. A decrease in activity of the enzymes involved in glycolysis and in the pentose phosphate shunt was also observed, suggesting that at the end of exogenous vitellogenesis the necessity of energy and reducing power has decreased compared to the situation at the onset of this period.
• 3.3. The main changes observed in gonad during vitellogenesis were the decreased activity of glycolysis and the pentose phosphate shunt as well as increased glycogen levels. The stored glycogen should be used later in association with the embryo development.
• 4.4. No major changes were observed in kidney metabolism throughout the vitellogenic process.
• 5.5. Exogenous vitellogenesis in rainbow trout is mainly associated with increased glycogen levels in the gonad and decreased metabolic activity in the liver.

     

Anaerobic rat heart. Effects of glucose and tricarboxylic acid-cycle metabolites on metabolism and physiological performance

1. The ability of tricarboxylic acid-cycle metabolites to influence the physiological performance of the perfused anaerobic rat heart was investigated. Energy expenditure/h [(beats/min)×60×systolic pressure/g of protein] for various anoxic conditions compared with oxygenated control hearts were: 5mm-glucose, 4.5%; 20mm- or 40mm-glucose, 10%; 20mm-glucose plus fumerate+malate+glutamate, 29%; 20mm-glucose plus oxaloacetate and α-oxoglutarate, 31%. 2. The energy expenditure/lactate production ratio was increased by the tricarboxylic acid-cycle metabolites, indicating that alterations in anaerobic physiological performance did not result from changes in glycolysis. 3. Analysis of tissue constituents provided further indication of an enhanced energy status for fumarate+malate+glutamate- and oxaloacetate+α-oxoglutarate-perfused hearts; tissue concentrations of both glycogen and ATP were higher than in the 20mm-glucose-perfused groups. 4. A marked increase in the accumulation of succinate in tissues perfused with oxaloacetate+α-oxoglutarate or fumarate+malate+glutamate provided further evidence that these metabolites were stimulating mitochondrial energy production under anoxia. 5. These studies indicate that mitochondrial ATP production can be stimulated in an isolated mammalian tissue perfused under anaerobiosis with a resulting enhancement of cell function.     

Purification and characterization of glycogen phosphorylase A and B from the freeze-avoiding gall moth larvae Epiblema scudderiana

The active a and inactive b forms of glycogen phosphorylase from cold-hardy larvae of the gall moth, Epiblema scudderiana, were purified using DEAE⁺ ion exchange and 3-5-AMP-agarose affinity chromatography. Maximum activities for glycogen phosphorylases a and b were 6.3±0.74 and 2.7±0.87 mol glucose-1-P·min^-1·g wet weight^-1, respectively, in -4°C-acclimated larvae. Final specific activities of the purified enzymes were 396 and 82 units·mg protein^-1, respectively. Both enzymes were dimers with native molecular weights of 215000±18000 for glycogen phosphorylase a and 209000±15000 for glycogen phosphorylase b; the subunit molecular weight of both forms was 87000±2000. Both enzymes showed pH optima of 7.5 at 22°C and a break in the Arrhenius relationship with a two- to four-fold increase in activation energy below 10°C. Michaelis constant values for glycogen at 22°C were 0.12±0.004 mg·ml^-1 for glycogen phosphorylase a and 0.87±0.034 mg·ml^-1 for glycogen phosphorylase b; the Michaelis constant for inorganic phosphate was 6.5±0.07 mmol·l^-1 for glycogen phosphorylase a and 23.6 mmol·l^-1 for glycogen phosphorylase b. Glycogen phosphorylase b was activated by adenosine monophosphate with a K _a of 0.176±0.004 mmol·l^-1. Michaelis constant and K _a values decreased by two- to fivefold at 5°C compared with 22°C. Glycerol had a positive effect on the Michaelis constant for glycogen for glycogen phosphorylase a at intermediate concentrations (0.5 mol·l^-1) but was inhibitory to both enzyme forms at high concentrations (2 mol·l^-1). Glycerol production as a cryoprotectant in E. scudderiana larvae is facilitated by the low temperature-simulated glycogen phosphorylase b to glycogen phosphorylase a conversion and by positive effects of low temperature on the kinetic properties of glycogen phosphorylase a. Enzyme shut-down when polyol synthesis is complete appears to be aided by strong inhibitory effects of glycerol and KCl on glycogen phosphorylase b.Abbreviations E _a activation energy - GPa glycogen phosphorylase a - GPb glycogen phosphorylase b - h Hill coefficient - I ₅₀ concentration of inhibitor that reduces enzymes velocity by 50% - K _a concentration of activator that produces half-maximal activation of enzyme activity - K _m Michaelis-Menten substrate affinity constant - MW molecular weight - PEG polyethylene glycol - P_i morganic phosphate - SDS PAGE sodium dodecyl sulphate polyacrylamide gel electrophoresis - V _max enzyme maximal velocity     

Subcellular localization of hexokinases I and II directs the metabolic fate of glucose

Background

The first step in glucose metabolism is conversion of glucose to glucose 6-phosphate (G-6-P) by hexokinases (HKs), a family with 4 isoforms. The two most common isoforms, HKI and HKII, have overlapping tissue expression, but different subcellular distributions, with HKI associated mainly with mitochondria and HKII associated with both mitochondrial and cytoplasmic compartments. Here we tested the hypothesis that these different subcellular distributions are associated with different metabolic roles, with mitochondrially-bound HK''s channeling G-6-P towards glycolysis (catabolic use), and cytoplasmic HKII regulating glycogen formation (anabolic use).

Methodology/Principal Findings

To study subcellular translocation of HKs in living cells, we expressed HKI and HKII linked to YFP in CHO cells. We concomitantly recorded the effects on glucose handling using the FRET based intracellular glucose biosensor, FLIPglu-600 mM, and glycogen formation using a glycogen-associated protein, PTG, tagged with GFP. Our results demonstrate that HKI remains strongly bound to mitochondria, whereas HKII translocates between mitochondria and the cytosol in response to glucose, G-6-P and Akt, but not ATP. Metabolic measurements suggest that HKI exclusively promotes glycolysis, whereas HKII has a more complex role, promoting glycolysis when bound to mitochondria and glycogen synthesis when located in the cytosol. Glycogen breakdown upon glucose removal leads to HKII inhibition and dissociation from mitochondria, probably mediated by increases in glycogen-derived G-6-P.

Conclusions/Significance

These findings show that the catabolic versus anabolic fate of glucose is dynamically regulated by extracellular glucose via signaling molecules such as intracellular glucose, G-6-P and Akt through regulation and subcellular translocation of HKII. In contrast, HKI, which activity and regulation is much less sensitive to these factors, is mainly committed to glycolysis. This may be an important mechanism by which HK''s allow cells to adapt to changing metabolic conditions to maintain energy balance and avoid injury.     

Liver metabolism in cold hypoxia: a comparison of energy metabolism and glycolysis in cold-sensitive and cold-resistant mammals

The effects of cold hypoxia were examined during a time-course at 2 °C on levels of glycolytic metabolites: glycogen, glucose, glucose-1-phosphate, glucose-6-phosphate, fructose-6-phosphate, fructose-1,6-bisphosphate, phosphoenolpyruvate, pyruvate, lactate and energetics (ATP, ADP, AMP) of livers from rats and columbian ground squirrels. Responses of adenylate pools reflected the energy imbalance created during cold hypoxia in both rat and ground squirrel liver within minutes of organ isolation. In rat, ATP levels and energy charge values for freshly isolated livers were 2.54 mol·g^-1 and 0.70, respectively. Within 5 min of cold hypoxia, ATP levels had dropped well below control values and by 8 h storage, ATP, AMP, and energy charge values were 0.21 mol·g^-1, 2.01 mol·g^-1, and 0.17, respectively. In columbian ground squirrels the patterns of rapid ATP depletion and AMP accumulation were similar to those found in rat. In rat liver, enzymatic regulatory control of glycolysis appeared to be extremely sensitive to the decline in cellular energy levels. After 8 h cold hypoxia levels of fructose-6-phosphate decreased and fructose-1,6-bisphosphate increased, thus reflecting an activation of glycolysis at the regulatory step catalysed by phospho-fructokinase fructose-1,6-bisphosphatase. Despite an initial increase in flux through glycolysis over the first 2 min (lactate levels increased 3.7 mol·g^-1), further flux through the pathway was not permitted even though glycolysis was activated at the phosphofructokinase/fructose-1,6-bisphosphatase locus at 8 h, since supplies of phosphorylated substrate glucose-1-phosphate or glucose-6-phosphate remained low throughout the duration of the 24-h period. Conversely, livers of Columbian ground squirrels exhibited no activation or inactivation of two key glycolytic regulatory loci, phosphofructokinase/fructose-1,6-bisphosphatase and pyruvate kinase/phosphoenolpyruvate carboxykinase and pyruvate carboxylase. Although previous studies have shown similar allosteric sensitivities to adenylates to rat liver phospho-fructokinase, there was no evidence of an activation of the pathway as a result of decreasing high energy adenylate, ATP or increasing AMP levels. The lack of any apparent regulatory control of glycosis during cold hypoxia may be related to hibernator-specific metabolic adaptations that are key to the survival of hypothermia during natural bouts of hibernation.Abbreviations DHAP dihydroxyacetonephosphate - EC energy charge - F1,6P₂ fructose-1,6-bisphosphate - F2,6P₂ fructose-2,6-bisphosphate - F6P fructose-6-phosphate - FBP fructose-1,6-bisphosphatase - G1P glucose-1-phosphate - G6P glucose-6-phosphate - GAP glyceraldehyde-3-phosphate - GAPDH glyceraldehyde-3-phosphate dehydrogenase - L/R lactobionate/raffinose-based solution - MR metabolic rate - PDH pyruvate dehydrogenase - PEP phosphoenolpyruvate - PEPCK & PC phosphoenolpyruvate carboxykinase and pyruvate carboxylase - PFK phosphofructokinase; PK, pyruvate kinase - Q ₁₀ the effect of a 10 °C drop in temperature on reaction rates (generally, Q ₁₀=2–3) - TA total adenylates - UW solution University of Wisconsin solution (L/R-based)     

A comparative study on the responses of the gills of two mudskippers to hypoxia and anoxia

A comparison of branchial enzyme profiles indicates that the gills of Periophthalmodon schlosseri would have a greater capacity for energy metabolism through glycolysis than those of Boleophthalmus boddaerti. Indeed, after exposure to hypoxia, or anoxia, there were significant increases in the lactate content in the gills of P. schlosseri. In addition, exposure to hypoxia or anoxia significantly lowered the glycogen level in the gills of this mudskipper. It can be deduced from these results that the glycolytic flux was increased to compensate for the decrease in ATP production through anaerobic glycolysis. Different from P. schlosseri, although there was an increase in lactate production in the gills of B. boddaerti exposed to hypoxia, there was no significant change in the branchial glycogen content, indicating that a reversed Pasteur effect might have occurred under such conditions. In contrast, anoxia induced an accumulation of lactate and a decrease in glycogen in the gills of B. boddaerti. Although lactate production in the gills of these mudskippers during hypoxia was inhibited by iodoacetate, the decreases in branchial glycogen contents could not account for the amounts of lactate formed. The branchial fructose-2,6-bisphosphate contents of these mudskippers exposed to hypoxia or anoxia decreased significantly, leaving phosphofructokinase and glycolytic rate responsive to cellular energy requirements under such conditions. The differences in response in the gills of B. boddaerti and P. schlosseri to hypoxia were possibly related to the distribution of phosphofructokinase between the free and bound states.Abbreviations ADP adenosine diphosphate - ALD aldolase - ALT alanine transaminase - AST aspartate transaminase - ATP adenosine triphosphate - CS citrate synthase - EDTA ethylenediaminetetra-acetic acid - EGTA ethylene glycol tetra-acetic acid - F6P fructose-6-phosphate - F-1,6-P₂ fructose-1,6-bisphosphate - F-2,6-P₂ fructose-2,6-bisphosphate - FBPase fructose-1,6-bisphosphatese - GAPDH glyceraldehyde-3-phosphate dehydrogenase - GDH glutamate dehydrogenase - -GDH -glycerophosphate dehydrogenase - GPase glycogen phosphorylase - HK hexokinase - HOAD 3-hydroxyacyl-CoA dehydrogenase - IDH isocitrate dehydrogenase - IOA iodoacetic acid - LDH lactate dehydrogenase - LO lactate oxidizing activity - MDH malate dehydrogenase - 3-PG 3-phosphoglyceric acid - PEP phosphoenolpyruvate - PEPCK phosphoenolpyruvate carboxykinase - PGI phosphoglucose isomerase - PGK phosphoglycerate kinase - PFK 6-phosphofructo-1-kinase - PIPES piperazine-N, N-bis-(2-ethanesulphonic acid) - PK pyruvate kinase - PMSF phenylmethylsulphonyl fluoride - PR pyrurate reducing activity - SE standard error - SW seawater - TPI triosephosphate isomerase     

Glycolysis–respiration relationships in a neuroblastoma cell line

Background

Although some reciprocal glycolysis–respiration relationships are well recognized, the relationship between reduced glycolysis flux and mitochondrial respiration has not been critically characterized.

Methods

We concomitantly measured the extracellular acidification rate (ECAR) and oxygen consumption rate (OCR) of SH-SY5Y neuroblastoma cells under free and restricted glycolysis flux conditions.

Results

Under conditions of fixed energy demand ECAR and OCR values showed a reciprocal relationship. In addition to observing an expected Crabtree effect in which increasing glucose availability raised the ECAR and reduced the OCR, a novel reciprocal relationship was documented in which reducing the ECAR via glucose deprivation or glycolysis inhibition increased the OCR. Substituting galactose for glucose, which reduces net glycolysis ATP yield without blocking glycolysis flux, similarly reduced the ECAR and increased the OCR. We further determined how reduced ECAR conditions affect proteins that associate with energy sensing and energy response pathways. ERK phosphorylation, SIRT1, and HIF1a decreased while AKT, p38, and AMPK phosphorylation increased.

Conclusions

These data document a novel intracellular glycolysis–respiration effect in which restricting glycolysis flux increases mitochondrial respiration.

General significance

Since this effect can be used to manipulate cell bioenergetic infrastructures, this particular glycolysis–respiration effect can practically inform the development of new mitochondrial medicine approaches.     

Mechanisms whereby glucose deprivation triggers metabolic preconditioning in the isolated rat heart

Transient glucose deprivation of the heart [GLU (-)] confers a preconditioning-like protection against subsequent ischemic/reperfusion (I/R). The mechanisms involved remain unclear. We hypothesized that GLU (-) would induce the classic ischemic preconditioning activated signaling cascade. Potential metabolic consequences and putative cell signaling events induced by transient glucose deprivation were evaluated as candidate mediators of this cardioprotection.Isolated glucose-perfused rat hearts were subjected to 30 min global ischemia followed by 30 min reperfusion (index I/R). Cardiac contractile recovery following I/R was used as the functional end-point in these studies. Metabolic preconditioning was stimulated by 15 min GLU (-) followed by 10 min glucose repletion prior to the index I/R. The potential metabolic consequences of GLU (-) were evaluated by using excess octanoate (11 mM OCT Hi) or 11 mM 2-deoxy-D-glucose (2-DG) in place of GLU (-) and by combining GLU (-) with fuels known to inhibit glycolysis supply (20 mM pyruvate or 1 mM octanoate, OCT Lo). The roles of -adrenoceptors, -adrenoceptors, adenosine receptors, protein kinase C (PKC) and mitochondrial K_ATP channels were investigated using inhibitors prazosin (10 M), propranolol (10 M), 8-(p-sulfophenyl) theophylline, (SPT 100 M), chelerythrine (CHEL 10 M) and 5-hydroxydecanoate (5 HD 100 M) respectively.GLU (-) increased mechanical recovery (59.8 ± 4.0 vs. 32.3 ± 4.7%; p < 0.01). Protection was abolished by pyruvate 26.6 ± 3.1; SPT 36.6 ± 3.0; CHEL 35 ± 4.8 or 5 HD 23.8 ± 3.3%. In a separate set of experiments, the specificity of SPT in this model was tested by preconditioning with adenosine (100 M) (34.7 ± 4 vs. control 16.8 ± 1.3%, p = 0.01) and blocking this protection with the same dose of SPT (16.3 ± 1.5%) used in the GLU (-) studies. Protection was unaltered by prazosin (50.2 ± 3.3%), propranolol (55.5 ± 4.0%), or OCT Lo (50.2 ± 2.5%). Protection was not mimicked by OCT Hi (35.6 ± 3.8%) or 2-DG (34 ± 4.3%).Transient glucose deprivation does not seem to achieve preconditioning-like cardioprotection by decreased glycolysis. Rather, the signal system may involve enhanced adenosine release, PKC, and activation of the mitochondrial K_ATP channel.     

Energetics of Anaerobic Sodium Transport by the Fresh Water Turtle Bladder

Certain of the metabolic events associated with anaerobic sodium transport by the isolated bladder of the fresh water turtle have been investigated. The data suggest that energy for this transport arises from glycolysis and that endogenous glycogen was the major and perhaps the sole source of substrate. The rate of anaerobic glycolysis, as determined by lactate formation, correlates well with the rate as determined by glycogen utilization. Using lactate formation as the index of anaerobic glycolysis, a linear relationship was observed between glycolysis and net anaerobic sodium transport. In the absence of sodium transport, glycolysis decreased by approximately 45 per cent. Tissue ATP concentrations were maintained at about the same level under anaerobic as under aerobic conditions. Finally if it is assumed that in the conversion of glycogen to lactate anaerobically, 3 moles of ATP are generated per mole of glucose residue, an average of over 15 equivalents of sodium were transported for every mole of ATP generated.