Letters to the Editor

1998 ◽  
Vol 275 (2) ◽  
pp. H726-H729
Author(s):  
J. A. L. Jeneson ◽  
M. J. Kushmerick ◽  
H. V. Westerhoff
Keyword(s):  
Oxygen Consumption ◽  
Steady State ◽  
Western Blot ◽  
Northern Blot ◽  
Adenine Nucleotide ◽  
Respiratory Control ◽  
High Energy ◽  
High Energy Phosphates ◽  
Adenine Nucleotide Translocator

The following is the abstract of the article discussed in the subsequent letter: Portman, Michael A., Yun Xiao, Ying Song, and Xue-Han Ning. Expression of adenine nucleotide translocator parallels maturation of respiratory control in heart in vivo. Am. J. Physiol. 273 ( Heart Circ. Physiol. 42): H1977–H1983, 1997.—Changes in the relationship between myocardial high-energy phosphates and oxygen consumption in vivo occur during development, implying that the mode of respiratory control undergoes maturation. We hypothesized that these maturational changes in sheep heart are paralleled by alterations in the adenine nucleotide translocator (ANT), which are in turn related to changes in the expression of this gene. Increases in myocardial oxygen consumption (MV˙o 2) were induced by epinephrine infusion in newborn (0–32 h, n = 6) and mature sheep (30–32 days, n = 6), and high-energy phosphates were monitored with 31P nuclear magnetic resonance. Western blot analyses for the ANT1 and the β-subunit of F1-adenosinetriphosphatase (ATPase) were performed in these hearts and additional ( n = 9 total per group) as well as in fetal hearts (130–132 days of gestation, n = 5). Northern blot analyses were performed to assess for changes in steady-state RNA transcripts for these two genes. Kinetic analyses for the31P spectra data revealed that the ADP-MV˙o 2 relationship for the newborns conformed to a Michaelis-Menten model but that the mature data did not conform to first- or second-order kinetic control of respiration through ANT. Maturation from fetal to mature was accompanied by a 2.5-fold increase in ANT protein (by Western blot), with no detectable change in β-F1-ATPase. Northern blot data show that steady-state mRNA levels for ANT and β-F1-ATPase increased ∼2.5-fold from fetal to mature. These data indicate that 1) respiratory control pattern in the newborn is consistent with a kinetic type regulation through ANT, 2) maturational decreases in control through ANT are paralleled by specific increases in ANT content, and 3) regulation of these changes in ANT may be related to increases in steady-state transcript levels for its gene.

Expression of adenine nucleotide translocator parallels maturation of respiratory control in heart in vivo

1997 ◽  
Vol 273 (4) ◽  
pp. H1977-H1983 ◽  
Author(s):  
Michael A. Portman ◽  
Yun Xiao ◽  
Ying Song ◽  
Xue-Han Ning
Keyword(s):  
Oxygen Consumption ◽  
Steady State ◽  
Western Blot ◽  
Northern Blot ◽  
Adenine Nucleotide ◽  
Respiratory Control ◽  
High Energy ◽  
High Energy Phosphates ◽  
Adenine Nucleotide Translocator

Changes in the relationship between myocardial high-energy phosphates and oxygen consumption in vivo occur during development, implying that the mode of respiratory control undergoes maturation. We hypothesized that these maturational changes in sheep heart are paralleled by alterations in the adenine nucleotide translocator (ANT), which are in turn related to changes in the expression of this gene. Increases in myocardial oxygen consumption (MV˙o 2) were induced by epinephrine infusion in newborn (0–32 h, n = 6) and mature sheep (30–32 days, n = 6), and high-energy phosphates were monitored with 31P nuclear magnetic resonance. Western blot analyses for the ANT1 and the β-subunit of F1-adenosinetriphosphatase (ATPase) were performed in these hearts and additional ( n = 9 total per group) as well as in fetal hearts (130–132 days of gestation, n = 5). Northern blot analyses were performed to assess for changes in steady-state RNA transcripts for these two genes. Kinetic analyses for the31P spectra data revealed that the ADP-MV˙o 2 relationship for the newborns conformed to a Michaelis-Menten model but that the mature data did not conform to first- or second-order kinetic control of respiration through ANT. Maturation from fetal to mature was accompanied by a 2.5-fold increase in ANT protein (by Western blot), with no detectable change in β-F1-ATPase. Northern blot data show that steady-state mRNA levels for ANT and β-F1-ATPase increased ∼2.5-fold from fetal to mature. These data indicate that 1) respiratory control pattern in the newborn is consistent with a kinetic type regulation through ANT, 2) maturational decreases in control through ANT are paralleled by specific increases in ANT content, and 3) regulation of these changes in ANT may be related to increases in steady-state transcript levels for its gene.

Transient changes in muscle high-energy phosphates during moderate exercise

1993 ◽  
Vol 75 (2) ◽  
pp. 648-656 ◽  
Author(s):  
G. D. Marsh ◽  
D. H. Paterson ◽  
J. J. Potwarka ◽  
R. T. Thompson
Keyword(s):  
Oxygen Consumption ◽  
Steady State ◽  
Recovery Period ◽  
High Energy ◽  
Second Order ◽  
Moderate Intensity ◽  
High Energy Phosphates ◽  
Order Model ◽  
Time Constants ◽  
First Order

The purpose of this study was to use 31P-nuclear magnetic resonance spectroscopy to examine changes in wrist flexor muscle metabolism during the transitions from rest to steady-state exercise (on-transient) and back to rest (off-transient). Five healthy young males (mean age 25 +/- 2 yr) performed a series of square-wave exercise tests, each consisting of 5 min of moderate-intensity work followed by a 5-min recovery period. The subjects repeated this protocol six times, and each individual's results were pooled before analysis. ATP and intracellular pH did not change significantly during exercise or recovery. Phosphocreatine (PCr) declined progressively at the onset of exercise, reaching a plateau after approximately 2 min. A reciprocal increase in Pi occurred during the onset of exercise. During the recovery period PCr was resynthesized, whereas Pi returned to resting levels. The data were plotted as a function of time and fit with both first- and second-order exponential growth or decay models; however, the second-order model did not significantly improve the fit of the data. Time constants for the first-order model of the on- and off-transient responses for both PCr and Pi were approximately 30 s. These values are nearly identical to the time constants for oxygen consumption during submaximal exercise that have been reported previously by several authors. The results of this study show that the metabolism of muscle PCr during steady-state exercise and recovery can be accurately described by a monoexponential model and, further, suggest that a first-order proportionality exists between metabolic substrate utilization and oxygen consumption.

scholarly journals Thyroid Hormone Coordinates Respiratory Control Maturation and Adenine Nucleotide Translocator Expression in Heart In Vivo

Circulation ◽  
2000 ◽  
Vol 102 (11) ◽  
pp. 1323-1329 ◽  
Author(s):  
Michael A. Portman ◽  
Yun Xiao ◽  
Kun Qian ◽  
Russell L. Tucker ◽  
Steven M. Parish ◽  
...  
Keyword(s):  
Thyroid Hormone ◽  
Adenine Nucleotide ◽  
Respiratory Control ◽  
Adenine Nucleotide Translocator

scholarly journals Efficiency of human skeletal muscle in vivo: comparison of isometric, concentric, and eccentric muscle action

1997 ◽  
Vol 83 (3) ◽  
pp. 867-874 ◽  
Author(s):  
T. W. Ryschon ◽  
M. D. Fowler ◽  
R. E. Wysong ◽  
A.-R. Anthony ◽  
R. S. Balaban
Keyword(s):  
Skeletal Muscle ◽  
Steady State ◽  
Production Rate ◽  
Human Skeletal Muscle ◽  
Atp Synthesis ◽  
High Energy ◽  
High Energy Phosphates ◽  
Muscle Action ◽  
Atp Production

Ryschon, T. W., Fowler, R. E. Wysong, A.-R. Anthony, and R. S. Balaban. Efficiency of human skeletal muscle in vivo: comparison of isometric, concentric, and eccentric muscle action. J. Appl. Physiol. 83(3): 867–874, 1997.—The purpose of this study was to estimate the efficiency of ATP utilization for concentric, eccentric, and isometric muscle action in the human tibialis anterior and extensor digitorum longus in vivo. A dynamometer was used to quantitate muscle work, or tension, while simultaneous 31P-nuclear magnetic resonance data were collected to monitor ATP, phosphocreatine, inorganic phosphate, and pH. The relative efficiency of the actions was estimated in two ways: steady-state effects on high-energy phosphates and a direct comparison of ATP synthesis rates with work. In the steady state, the cytosolic free energy dropped to the lowest value with concentric activity, followed by eccentric and isometric action for comparative muscle tensions. Estimates of ATP synthesis rates revealed a mechanochemical efficiency [i.e., ATP production rate/work (both in J/s)] of 15.0 ± 1.3% in concentric and 34.7 ± 6.1% in eccentric activity. The estimated maximum ATP production rate was highest in concentric action, suggesting an activation of energy metabolism under these conditions. By using direct measures of metabolic strain and ATP turnover, these data demonstrate a decreasing metabolic efficiency in human muscle action from isometric, to eccentric, to concentric action.

scholarly journals The Flux from Glucose to Glutamate in the Rat Brain in vivo as Determined by 1-Observed, 13C-Edited NMR Spectroscopy

1990 ◽  
Vol 10 (2) ◽  
pp. 170-179 ◽  
Author(s):  
Susan M. Fitzpatrick ◽  
Hoby P. Hetherington ◽  
Kevin L. Behar ◽  
Robert G. Shulman
Keyword(s):  
Steady State ◽  
Nmr Spectroscopy ◽  
Rat Brain ◽  
Tca Cycle ◽  
Difference Spectrum ◽  
Order Rate Constant ◽  
High Energy ◽  
High Energy Phosphates ◽  
Measured Intensity

The rate of incorporation of carbon from [1-13C]glucose into the [4-CH2] and [3-CH2] of cerebral glutamate was measured in the rat brain in vivo by 1H-observed, 13C-edited (POCE) nuclear magnetic resonance (NMR) spectroscopy. Spectra were acquired every 98 s during a 60-min infusion of [1-13C]glucose. Complete time courses were obtained from six animals. The measured intensity of the unresolved [4-13CH2] resonances of glutamate and glutamine increased exponentially during the infusion and attained a steady state in ∼20 min with a first-order rate constant of 0.130 ± 0.010 min−1 (t1/2 = 5.3 ± 0.5 min). The appearance of the [3-13CH2] resonance in the POCE difference spectrum lagged behind that of the [4-13CH2] resonance and had not reached steady state at the end of the 60-min infusion (t1/2 = 26.6 ± 4.1 min). The increase observed in 13C-labeled glutamate represented isotopic enrichment and was not due to a change in the total glutamate concentration. The glucose infusion did not affect the levels of high-energy phosphates or intracellular pH as determined by 31P NMR spectroscopy. Since glucose carbon is incorporated into glutamate by rapid exchange with the tricarboxylic acid (TCA) cycle intermediate α-ketoglutarate, the rate of glutamate labeling provided an estimate of TCA cycle flux. We have determined the flux of carbon through the TCA cycle to be ≈1.4 μmol g−1 min−1. These experiments demonstrate the feasibility of measuring metabolic fluxes in vivo using 13C-labeled glucose and the technique of 1H-observed, 13C-decoupled NMR spectroscopy.

Direct action of T3on phosphorylation potential in the sheep heart in vivo

2005 ◽  
Vol 288 (5) ◽  
pp. H2484-H2490 ◽  
Author(s):  
Michael A. Portman ◽  
Kun Qian ◽  
Julia Krueger ◽  
Xue-Han Ning
Keyword(s):  
Respiratory Rate ◽  
Adenine Nucleotide ◽  
Median Sternotomy ◽  
High Energy ◽  
Utilization Efficiency ◽  
High Energy Phosphates ◽  
High Energy Phosphate ◽  
Phosphorylation Potential ◽  
Nongenomic Action

Thyroid acting through ligand binding to nuclear receptors modifies myocardial respiratory kinetics and oxidative phosphorylation in the heart. Direct nongenomic action of thyroid hormone on high-energy phosphate concentrations and respiratory kinetics has never been proven in vivo but might be responsible for observed changes in oxygen utilization efficiency immediately after triiodothyronine (T3) administration. We tested the hypothesis that T3directly and rapidly modifies myocardial high-energy phosphate concentrations and phosphorylation potential in vivo. Anesthetized sheep (age 28–40 days) thyroidectomized shortly after birth (Thy) and euthyroid age-matched controls (Con) underwent median sternotomy and received T3infusion (0.8 μg/kg), followed by epinephrine infusion to increase myocardial oxygen consumption (MV̇o2).31P magnetic resonance spectra were monitored via a surface coil over the left ventricle. T3increased phosphocreatine (PCr)/ATP and decreased ADP in Thy animals without causing a change in MV̇o2. T3produced no changes in high-energy phosphates in Con animals. T3did not modify the PCr/ATP or ADP response to epinephrine and elevation in MV̇o2in either group. Cardiac mitochondria isolated from Thy and Con animals showed no change in respiratory rate or ADP/ATP exchange efficiency after T3incubation. T3infusion in a hypothyroid state decreases ADP concentration, thereby altering the equilibrium between phosphorylation potential and myocardial respiratory rate. These T3-induced effects are not due to changes in ADP/ATP exchange efficiency through action at the adenine nucleotide translocator but may be due to T3mediation of substrate utilization, confirmed in other models.

Reduced substrate oxidation in postischemic myocardium: 13C and 31P NMR analyses

1990 ◽  
Vol 258 (5) ◽  
pp. H1357-H1365 ◽  
Author(s):  
E. D. Lewandowski ◽  
D. L. Johnston
Keyword(s):  
Steady State ◽  
31P Nmr ◽  
Tca Cycle ◽  
High Energy ◽  
Substrate Oxidation ◽  
High Energy Phosphates ◽  
Atp Content ◽  
And Control ◽  
13C And 31P Nmr ◽  
Postischemic Myocardium

13C and 31P nuclear magnetic resonance (NMR) spectra were used to assess substrate oxidation and high-energy phosphates in postischemic (PI) isolated rabbit hearts. Phosphocreatine (PCr) increased in nonischemic controls on switching from glucose perfusion to either 2.5 mM [3-13C]pyruvate (120%, n = 7) or [2-13C]acetate (114%, n = 8, P less than 0.05). ATP content, oxygen consumption (MVO2), and hemodynamics (dP/dt) were not affected by substrate availability in control or PI hearts. dP/dt was 40-60% lower in PI hearts during reperfusion after 10 min ischemia. Hearts reperfused with either pyruvate (n = 11) or acetate (n = 8) regained preischemic PCr levels within 45 s. Steady-state ATP levels were 55-70% of preischemia with pyruvate and 52-60% with acetate. Percent maximum [4-13C]glutamate signal showed reduced conversion of pyruvate to glutamate via the tricarboxylic acid (TCA) cycle at 4-min reperfusion (PI = 24 +/- 4%, means +/- SE; Control = 48 +/- 4%). The increase in 13C signal from the C-4 position of glutamate was similar to control hearts within 10.5 min. The increase in [4-13C]glutamate signal from acetate was not different between PI and control hearts. The ratio of [2-13C]Glu:[4-13C]Glu, reflecting TCA cycle activity, was reduced in PI hearts with acetate for at least 10 min (Control = 0.76 +/- 0.03; PI = 0.51 +/- 0.09) until steady state was reached. Despite rapid recovery of oxidative phosphorylation, contractility remained impaired and substrate oxidation was significantly slowed in postischemic hearts.

Metabolic and energy correlates of intracellular pH in progressive fatigue of squid (L. brevis) mantle muscle

1996 ◽  
Vol 271 (5) ◽  
pp. R1403-R1414 ◽  
Author(s):  
H. O. Portner ◽  
E. Finke ◽  
P. G. Lee
Keyword(s):  
Free Energy ◽  
Critical Velocity ◽  
Energy Levels ◽  
High Energy ◽  
Swimming Velocity ◽  
High Energy Phosphates ◽  
Energy Status ◽  
Intracellular Acidosis ◽  
Model Calculations

Squid (Lolliguncula brevis) were exercised at increasing swimming speeds to allow us to analyze the correlated changes in intracellular metabolic, acid-base, and energy status of the mantle musculature. Beyond a critical swimming velocity of 1.5 mantle lengths/s, an intracellular acidosis developed that was caused by an initial base loss from the cells, the onset of respiratory acidification, and, predominantly, octopine formation. The acidosis was correlated with decreasing levels of phospho-L-arginine and, thus, supported ATP buffering at the expense of the phosphagen. Monohydrogenphosphate, the actual substrate of glycogen phosphorylase accumulated, enabling glycogen degradation, despite progressive acidosis. In addition to octopine, succinate, and glycerophosphate accumulation, the onset of acidosis characterizes the critical velocity and indicates the transition to a non-steady-state time-limited situation. Accordingly, swimming above the critical velocity caused cellular energy levels (in vivo Gibbs free energy change of ATP hydrolysis) to fall. A minimal value was reached at about -45 kJ/mol. Model calculations demonstrate that changes in free Mg2+ levels only minimally affect ATP free energy, but minimum levels are relevant in maintaining functional concentrations of Mg(2+)-complexed adenylates. Model calculations also reveal that phosphagen breakdown enabled L. brevis to reach swimming speeds about three times higher than the critical velocity. Comparison of two offshore squid species (Loligo pealei and Illex illecebrosus) with the estuarine squid L.brevis indicates that the latter uses a strategy to delay the exploitation of high-energy phosphates and protect energy levels at higher than the minimum levels (-42 kJ/mol) characterizing fatigue in the other species. A more economical use of anaerobic resources and an early reduction in performance may enable L. brevis to tolerate more extreme environmental conditions in shallow estuarine waters and even hypoxic environments and to prevent a fatal depletion of energy stores.

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