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Query: UMLS:C0015672 (fatigue)
 51,768 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The occurrence of an abrupt acceleration in phosphocreatine hydrolysis in the tibial anterior muscle during the last part of a sustained isometric exercise at 30% maximal voluntary contraction until fatigue is demonstrated in seven out of eight healthy subjects by applying in vivo 31P NMR spectroscopy at 1.5 T field strength. This additional third phase in PCr hydrolysis, is preceded by a common biphasic pattern (first fast then slow) in PCr use. The NMR spectra, as localized by a surface coil and improved by proton irradiation, were collected at a time resolution of 16 s. Mean rates of PCr hydrolysis during exercise were -0.44 +/- 0.19% s(-1), -0.07 +/- 0.04% s(-1), and -0.29 +/- 0.10% s(-1) for the three successive phases. The increased rate of PCr hydrolysis, and also the loss of fine force control evident in the force records are consistent with increased involvement of large, fast-fatiguable units later in the contraction.
NMR Biomed 2002 Jun
PMID:An additional phase in PCr use during sustained isometric exercise at 30% MVC in the tibialis anterior muscle. 1211 9

The identification of subcellular fluxes of exchange of ATP, phosphocreatine (PCr) and Pi between mitochondria, cytosol and ATPases and pathways of energy transfer in a whole organ is a challenge specially in the myocardium where 50% of creatine kinases (CK) are found in close vicinity of ATP producing (mito-CK) and utilizing (MM-bound CK) reactions. To dissect their contribution in cardiac energy transfer we recently developed a new experimental 31P NMR spectroscopy approach. This led to identify three kinetically different subcellular CKs and to evidence experimentally the CK shuttle in a rat heart perfused in isovolumy. Here we show that a decreased energy demand alters energetic pathways : two CKs (cytosolic and MM-bound) functioning at equilibrium and a non mitochondrial ATP<-->Pi exchange was sufficient to describe NMR data. Mito-CK fluxes was not detected anymore. This confirms the dependence of energy pathways upon cardiac activity. Indeed the subcellular localization and activity of CKs may have important bioenergetic consequences for the in vivo control of respiration at high work: free ADP estimated from global CK equilibrium might not always adequately reflect its concentration at the ANT.
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PMID:Identification of subcellular energy fluxes by P NMR spectroscopy in the perfused heart: contractility induced modifications of energy transfer pathways. 1224 Oct 52

The metabolism of high energy phosphates during muscular contraction due to direct electrical stimulation, indirect stimulation via nerve excitation, and magnetic stimulation was studied in isolated muscles (frog sartorius muscles) by (31)P nuclear magnetic resonance ((31)P-NMR). Twitch amplitudes elicited by each stimulus were measured alternatively at 3 mm displacement loading and 5 g weight. Both the creatine/inorganic phosphate (PCr/Pi) and pH changes were more marked in direct electrical stimulation than in magnetic stimulation. The muscular contraction caused by magnetic stimulation showed less fatigue than that caused by direct electrical muscular stimulation.
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PMID:Phosphate metabolites in muscular contraction caused by magnetic stimulation. 1282 Feb 94

Metabolic control within skeletal muscle is designed to limit ADP accumulation even during conditions where ATP demand is out of balance with ATP synthesis. This is accomplished by the reactions of adenylate kinase (AK; ADP+ADP <--> AMP+ATP) and AMP deaminase (AMP+H(2)O --> NH(3)+IMP), which limit ADP accumulation under these conditions. The purpose of this study was to determine whether AK deficiency (AK(-/-)) would result in sufficient ADP accumulation to be visible using (31)P-NMRS during the high energy demands of frequent in situ tetanic contractions. To do this we examined the high-energy phosphates of the gastrocnemius muscle in the knockout mouse with AK1(-/-) and wild-type (WT) control muscle over the course of 64 rapid (2/s) isometric tetanic contractions. Near-complete depletion of phosphocreatine was apparent after 16 contractions in both groups. By approximately 40 contractions, ADP was clearly visible in AK1(-/-) muscle. This transient concentration of the NMR visible free ADP was estimated to be approximately 1.7 mM, and represents the first time free ADP has been directly measured in contracting skeletal muscle. Such an increase in free ADP is severalfold greater than previously thought to occur. This large accumulation of free ADP also represents a significant reduction in energy available from ATP, and has implications on cellular processes that depend on a high yield of energy from ATP such as calcium sequestration. Remarkably, the AK1(-/-) and WT muscles exhibited similar fatigue profiles. Our findings suggest that skeletal muscle is surprisingly tolerant to a large increase in ADP and by extension, a decline in energy from ATP.
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PMID:31P-NMR observation of free ADP during fatiguing, repetitive contractions of murine skeletal muscle lacking AK1. 1568 8

We have designed and synthesized two photochromic compounds incorporating fused indoline and benzooxazine fragments. Variable-temperature 1H NMR spectroscopy demonstrates that their central [1,3]oxazine ring opens thermally with free energy barriers ranging from 14 to 19 kcal mol(-1). The ring-opened species reverts rapidly to the original isomer and can only be detected after chemical trapping. Specifically, the nucleophilic attack of a hydroxide anion to the indolium cation of the ring-opened species prevents re-isomerization. Laser excitation of both compounds induces the opening of the [1,3]oxazine ring in less than 6 ns with quantum yields up to 0.1. The photoinduced ring opening generates a 4-nitrophenolate chromophore, which absorbs strongly at 440 nm. The photogenerated species reverts to the original form with a lifetime of 22 ns for both compounds. Thus, these transformations can be exploited to interconvert the two isomers of each species with nanosecond switching speeds. Furthermore, thousands of switching cycles can be repeated consecutively without any sign of degradation, even in the presence of molecular oxygen. These processes can be reproduced efficiently in poly(methyl methacrylate) matrixes. Under these conditions, the thermal re-isomerization occurs with biexponential kinetics in submillisecond time scales. In principle, the fast isomerization kinetics and excellent fatigue resistance of both compounds offer the opportunity to modulate rapidly and efficiently a variety of molecular and macroscopic properties. Thus, our molecular design can evolve into the realization of a new family of photochromic compounds and materials with promising photoresponsive character.
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PMID:Fast and stable photochromic oxazines. 1627 45

The combined effects of intracellular lactate and proton accumulation on cell volume, Vc, were investigated in resting Rana temporaria striated muscle fibres. Intracellular lactate and H+ concentrations were simultaneously increased by exposing resting muscle fibres to extracellular solutions that contained 20-80 mm sodium lactate. Cellular H+ and lactate entry was confirmed using pH-sensitive electrodes and 1H-NMR, respectively, and effects on Vc were measured using confocal microscope xz-scanning. Exposure to extracellular lactate up to 80 mm produced significant changes in pH and intracellular lactate (from a pH of 7.24 +/- 0.03, n = 8, and 4.65 +/- 1.07 mm, n = 6, respectively, in control fibres, to 6.59 +/- 0.03, n = 4, and 26.41 +/- 0.92 mm, n = 3, respectively) that were comparable to those observed following fatiguing stimulation (6.30-6.70 and 18.04 +/- 1.78 mm, n = 6, respectively). Yet, the increase in intracellular osmolarity expected from such an increase in intracellular lactate did not significantly alter Vc. Simulation of these experimental results, modified from the charge difference model of Fraser & Huang, demonstrated that such experimental manoeuvres produced changes in intracellular [H+] and [lactate] comparable to those observed during muscle fatigue, and accounted for this paradoxical conservation of Vc through balancing negative osmotic effects resulting from the net cation efflux that would follow a titration of intracellular membrane-impermeant anions by the intracellular accumulation of protons. It demonstrated that with established physiological values for intracellular buffering capacity and the permeability ratio of lactic acid and anionic lactate, P(LacH): P(Lac-), this would provide a mechanism that precisely balanced any effect on cell volume resulting from lactate accumulation during exercise.
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PMID:The influence of intracellular lactate and H+ on cell volume in amphibian skeletal muscle. 1744 16

The root bark of Anisophyllea dichostyla R. Br. is traditionally used in the Democratic Republic Congo for the treatment of several conditions such as anorexia, fatigue and intestinal infections. We have identified and quantitated several polyphenol antioxidants in the methanol extract of the root bark (120g). The polyphenol content (3.32g/kg) was predominantly ellagitannins (25%) and polyhydroxyflavan-3-ols (catechins and procyanidins, 75%) with 3'-O-methyl-3,4-methylenedioxo ellagic acid 4'-O-beta-d-glucopyranoside and (-)-epicatechin as the major species in each class. These two compounds and the following species were identified unequivocally by NMR spectroscopy: (+)-catechin, (-)-epicatechin 3-O-gallate, 3-O-methyl ellagic acid, 3,3'-di-O-methyl ellagic acid, 3'-O-methyl-3,4-methylenedioxo ellagic acid, 3'-O-methyl-3,4-methylenedioxo ellagic acid 4'-O-beta-d-glucopyranoside, and 3'-O-methyl ellagic acid 4-O-beta-d-xylopyranoside. The following additional compounds were purified by semi-preparative HPLC and tentatively identified on the basis of UV spectra, HPLC-ESI-MS and nano-ESI-MS-MS: (+)-catechin-3-O-beta-d-glucopyranoside, epicatechin-(4beta-->8)-catechin (procyanidin B(1)), epicatechin-(4beta-->8)-epicatechin (procyanidin B(2)), an (epi)catechin trimer, 3-O-methyl ellagic acid 4-O-beta-d-glucopyranoside, (-)-epicatechin 3-O-vanillate, 3,4-methylenedioxo ellagic acid 4'-O- beta-d-glucopyranoside, and 3,3'-di-O-methyl ellagic acid 4-O-beta-d-xylopyranoside. Fractionation of the raw extract by column chromatography on silicic acid yielded 10 fractions. In the hypoxanthine/xanthine oxidase antioxidant assay system, CC-9 which contained a range of polyphenols dominated by (-)-epicatechin-O-gallate proved to be the most potent antioxidant fraction (IC(50)=52 micro g/mL) in terms of ROS scavenging. In terms of XO inhibition CC-8, dominated by (epi)catechin trimer and which also contained appreciable amounts of 3'-O-methyl ellagic acid 4'-O-beta-d-xylopyranoside, as well as the catechins (+)-catechin-3-O-beta-d-glucopyranoside, epicatechin-(4beta-->8)-catechin (procyanidin B(1)), and (-)-epicatechin 3-O-gallate, proved to be the most potent (IC(50)=36 micro g/mL).
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PMID:Isolation, purification and identification of ellagic acid derivatives, catechins, and procyanidins from the root bark of Anisophyllea dichostyla R. Br. 1708 99

Synthetic hydroxyapatite, HA [Ca10(PO4)6(OH)2], is a bioactive material that is chemically similar to biological apatite, the mineral phase of bone (a nanocomposite material). Synthetic biocomposites, comprising a polymer and hydroxyapatite that are used for bone replacement, have limitations when loaded under fatigue in that the weak mechanical bond between the two phases can result in failure at the interface. Chemical coupling of the HA and polymer matrix may provide a means of improving the interfacial bonding between the polymer and HA phases. Herein, we report our first steps toward developing chemically coupled nano-biocomposites via a two-step process. We describe the synthesis and characterization of surface-grafted hydroxyapatite (SG-HA), which possesses a reactive C=C functional group. In future work, we will report on the second step, namely the coupling of this functional group to a polymer by a copolymerization reaction to give a chemically coupled nano-biocomposite. The SG-HA reported herein was characterized by a range of methods including 31P and 13C magic-angle spinning (MAS)-NMR, Fourier transform infrared (FTIR), and Raman spectroscopy.
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PMID:Synthesis and characterization of grafted nanohydroxyapatites using functionalized surface agents. 1748 Jan 6

Traditionally, critical swimming speed has been defined as the speed when a fish can no longer propel itself forward, and is exhausted. To gain a better understanding of the metabolic processes at work during a U(crit) swim test, and that lead to fatigue, we developed a method using in vivo (31)P-NMR spectroscopy in combination with a Brett-type swim tunnel. Our data showed that a metabolic transition point is reached when the fish change from using steady state aerobic metabolism to non-steady state anaerobic metabolism, as indicated by a significant increase in inorganic phosphate levels from 0.3+/-0.3 to 9.5+/-3.4 mol g(-1), and a drop in intracellular pH from 7.48+/-0.03 to 6.81+/-0.05 in muscle. This coincides with the point when the fish change gait from subcarangiform swimming to kick-and-glide bursts. As the number of kicks increased, so too did the Pi concentration, and the pH(i) dropped. Both changes were maximal at U(crit). A significant drop in Gibbs free energy change of ATP hydrolysis from -55.6+/-1.4 to -49.8+/-0.7 kJ mol(-1) is argued to have been involved in fatigue. This confirms earlier findings that the traditional definition of U(crit), unlike other critical points that are typically marked by a transition from aerobic to anaerobic metabolism, is the point of complete exhaustion of both aerobic and anaerobic resources.
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PMID:An examination of the metabolic processes underpinning critical swimming in Atlantic cod (Gadus morhua L.) using in vivo 31P-NMR spectroscopy. 1795 15

Two novel photochromic bisthienylethene derivatives BTE-NA1 and BTE-NA2 with a six-membered aryl ring of naphthalimide fluorescent moiety as the center ethene bridging unit were synthesized and fully characterized by 1H NMR, 13C NMR, and HRMS. They exhibit considerably high cyclization quantum yield and good fatigue resistance. Interestingly, the fluorescence of BTE-NA1 arising from the naphthalimide unit could be well modulated by photochromism and solvatochromism. Quantum chemical calculations were carried out to study their geometrical, electronic, and optical properties, which were in good accordance with the experimental data. Furthermore, a combined NOR and INHIBIT logic operation based on BTE-NA1 has been successfully mimicked with fluorescence changes as outputs.
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PMID:Novel bisthienylethenes containing naphthalimide as the center ethene bridge: photochromism and solvatochromism for combined NOR and INHIBIT logic gates. 1936 89


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