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Query: UMLS:C0392674 (exhaustion)
 13,658 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Brain microtubules are found to disperse rods of skeletal muscle myosin and become decorated with amorphous aggregates of myosin. Then microtubules are partially depolymerized by myosin. Myosin shows high Mg2+-GTPase activity which is not influenced by microtubules, and induces the partial depolymerization of microtubules by exhaustion of GTP in the solution. H-meromyosin depolymerizes microtubules like myosin does. H-meromyosin is, however, contaminated with a trace amount of trypsin, which irreversibly depolymerizes microtubules.
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PMID:Depolymerization of brain microtubules by skeletal muscle myosin. 15 54

Chronic low-frequency stimulation (CLFS) of fast-twitch muscles induces fast-to-slow fiber-type transitions that differ in their extent in rat and rabbit. Fast-twitch muscle of the normal rat responds to CLFS with sequential transitions in myosin heavy chain (HC) expression in the order HCIIb --> HCIId --> HCIIa. However, in rabbit muscle the changes proceed beyond the state of HCIIa and include, as a final step, the expression of the slow myosin HCI. The time course for the transitions in myosin HC expression at both the messenger ribonucleic acid and protein levels suggests that fiber-type conversions occur asynchronously in a sequential manner. Thus type IIB fibers convert first to type IID fibers; these fibers then transform into type IIA fibers, which in rabbit muscle ultimately change into type I fibers. This sequence and the related changes in myosin isoforms point to different thresholds of the genes encoding the various fast and slow myosin HC isoforms. Although transformation of existing fast fibers into slower fibers is the major process that underlies the stimulation-induced fast-to-slow conversion, fiber replacement may also contribute. In rabbit muscle CLFS may cause metabolic exhaustion and subsequent deterioration in a fraction of the fast-twitch glycolytic fibers. For the most part these are replaced by satellite cell-derived, newly formed slow-twitch fibers.
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PMID:Fiber transformation and fiber replacement in chronically stimulated muscle. 142 Feb 21

Clinical heart preservation is currently limited to only 4-6 hr, while the kidney, liver, and pancreas can tolerate 24-48 hr of cold ischemia. A fundamental difference between these organs is that the heart is contractile, containing large quantities of actin and myosin, and is susceptible to contracture-induced injury caused by energy deprivation. We have quantified and correlated the onset of contracture with levels of ATP and glycogen during cold storage in rabbit hearts flushed with UW solution, with and without 1 mM calcium (Ca), or 3 mM iodoacetate (IAA). A fluid-filled left ventricular balloon was used to generate pressure-volume curves (compliance) at 1, 6, 12, 18, and 24 hr of cold storage. Onset of contracture occurred in UW stored hearts at 18 hr, contracture in hearts exposed to Ca occurred between 6 and 12 hr. Compliance was significantly less in hearts exposed to Ca at 12, 18, and 24 hr (P less than .01) than in hearts without Ca. ATP levels were well maintained for up to 18 hr in the hearts preserved in UW solution (78%), but fell more rapidly in the presence of Ca at 12 hr (P less than .005), 18 hr (P less than .005), and 24 hr (P less than .05). In comparison, the ATP supply of the liver and kidney was exhausted by only 4 hr of cold storage. Onset of myocardial contracture correlated with a decrease in ATP to less than 80% of control, and contracture accelerated ATP decline 3-6-fold. IAA caused nearly complete myocardial contracture and ATP depletion within 2 hr. Isolated heart function was 77% and 73% at 6 and 12 hr of storage, but fell to 54% and 42% at 18 and 24 hr, respectively, coinciding with development of contracture. We conclude that ischemic contracture in this model is a major cause of myocardial damage during cold storage, and is accelerated by the presence of Ca. Other organs can be successfully stored despite exhaustion of ATP reserves. Thus successful cold-storage of the heart is highly ATP-dependent. Since cold storage inevitably leads to ATP depletion, extension of myocardial ischemic tolerance will depend on either reversible inhibition of ATP hydrolysis during storage, reversible uncoupling of contracture development from ATP depletion, or maintaining ATP production by continuous hypothermic perfusion.
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PMID:Limitations of heart preservation by cold storage. 173 22

Metabolic fatigue is a characteristic muscle response to intense exercise that has outstripped the rate of ATP replacement. The accumulation of metabolic by-products, namely hydrogen ions and diprotonated phosphate, interferes with actin-myosin interaction, effectively preserving muscle ATP levels by preventing further ATP hydrolysis. Muscle force and metabolite concentrations return to normal in about 5 minutes. Less intense exercise causes a more subtle, non-metabolic fatigue due to a still-undefined disturbance of excitation-contraction coupling, which can last for several hours. In this type of fatigue, greater effort is required to generate submaximal forces. Endurance exercise is mainly limited by the size of muscle glycogen stores and how efficiently they are used. Endurance training permits an athlete to work aerobically at high rates, consuming a mixture of lipid and carbohydrate fuels. When muscle glycogen is used up, exercise can only continue at the relatively low rate supportable by lipid metabolism. Anaerobic exercise is also limited by subjective factors such as dyspnoea and muscle pain, which have objective determinants. Extremely prolonged exercise can lead to general collapse because of dehydration, hyperthermia, or hypoglycaemia. None of these factors explains the phenomenon of asthenia, a subjective sense of exhaustion that produces no objective impairment of physical performance. The metabolic myopathies are experiments of nature that promise to shed new light on the biochemical basis of muscle fatigue. This will require quantitative studies of the kind provided by topical magnetic resonance spectroscopy, correlating physiology and metabolism in vivo.
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PMID:Muscle metabolism during fatigue and work. 226 24

The responses of muscle spindles in the iliofibularis muscle of the cane toad Bufo marinus were examined during constant velocity stretch of the passive muscle. Spindles were found to show an 'initial burst' of high frequency impulses at the onset of stretch. Associated with the initial burst was a steep passive tension rise in the whole muscle, the short-range elastic component (Hill, 1968), called here the passive stiffness. The size of the initial burst was found to depend on muscle length in a similar way as whole-muscle tetanic tension. Repetitive stretch was found to reduce both the initial burst and passive stiffness. The time taken for both to return to their control values was 3 and 10 s respectively. If immediately following repetitive stretch the muscle, and hence the spindle, was held stretched for 3 s, the initial burst in response to a subsequent stretch from a shorter length remained reduced in size for 300 s. The depression could be reversed by a brief period of fusimotor stimulation. Hypertonic Ringer solutions were found to increase the initial burst and passive stiffness, while both were reduced in hypotonic solutions. Low concentrations of caffeine (1.5 mM) produced a similar decrease in both the initial burst and the passive stiffness. Calcium-free Ringer solution left the stiffness unchanged, and increased the whole dynamic response of the spindle. Metabolic exhaustion and poisoning of the muscle caused the initial burst to increase while decreasing the active tension. It is concluded that the initial burst is an intrafusal manifestation of the passive short-range stiffness of extrafusal muscle which is thought to be due to the formation of stable cross-bridges between the actin and myosin filaments of myofibrils.
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PMID:The initial burst of impulses in responses of toad muscle spindles during stretch. 293 46

The purpose of this study was to examine the Ca2+-Mg2+ myofibrillar ATPase and protein composition of cardiac and skeletal muscle following strenuous activity to voluntary exhaustion. Sprague-Dawley rats (200 g) were assigned to a control and exercised group, with the run group completing 25 m.min-1 and 8% grade for 1 hour. Following activity, the myocardial Ca2+-Mg2+ myofibrillar ATPase activity -pCa relationship had undergone a rightward shift in the curve. Electrophoretic analysis revealed a change in the pattern of cardiac myofibrillar protein bands, particularly in the 38-42 Kdalton region. Enzymatic analysis of myofibrillar proteins from plantaris muscle, revealed no change in Ca2+ regulation following exercise. Electronmicrographic and electrophoretic analysis revealed extensively disrupted sarcomeric structure and a change in the ratio of several plantaris myofibrillar proteins. No difference was observed for myosin: Actin: tropomyosin ratios; however a dramatic reduction in 58 and 95 Kdalton proteins were evident. The results indicate that prolonged running is associated with similar responses in cardiac and skeletal muscle myofibrillar protein compositions. The abnormalities in myofibrillar ultrastructure may implicate force transmission failure as a factor in exercised-induced muscle damage and/or fatigue.
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PMID:Influence of exercise on cardiac and skeletal muscle myofibrillar proteins. 297 50

In the process of defining the recruitment of fuel and pathway selection in rainbow trout fast-twitch white skeletal muscle, it was clear that the near-maximal myosin adenosinetriphosphatase activity during a 10-s sprint was supported solely by phosphocreatine hydrolysis. A conservative estimate of the ATP turnover was 188 mumol X g wet wt-1 X min-1. It was not until the rate and force of contraction decreased that the relative contribution of anaerobic glycogenolysis became increasingly important. Over a 10-min period of burst swimming at approximately 120% of maximum aerobic steady-state swimming velocity of trout determined in a Brett-type swim tunnel, fatigue was associated with the near-depletion of glycogen in white muscle. The ATP turnover supported by anaerobic glycogenolysis was 78 mumol X g wet wt-1 X min-1. The glycolytic pathway appeared functional at this time with control sites being identified at hexokinase and phosphofructokinase (PFK-1). PFK-1 did not appear to be inhibited by low muscle pH (pH 6.66). In another exercise protocol lasting 30 min, complete exhaustion was related to glycogen depletion. The sum of all glycolytic intermediates from glucose 6-phosphate to pyruvate at exhaustion decreased by a dramatic 80% compared with the 25% decrease for the 10-min fatigue swimming protocol. This large depletion of glycolytic intermediates was accompanied by an 80% fall in ATP, a 70-80% reduction in the ATP/ADP and phosphorylation potential, and a 2.5-fold increase in the NAD/NADH. Associated with these changes was a marked displacement of the phosphoglycerate kinase (PGK), and the combined glyceraldehyde-3-phosphate dehydrogenase-PGK reactions from thermodynamic equilibrium. As a general conclusion, fatigue and exhaustion should be viewed as a multicomponent biochemical process in response to low glycogen and not leveled at one particular step of the glycolytic pathway.
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PMID:Regulation of anaerobic ATP-generating pathways in trout fast-twitch skeletal muscle. 360 83

Six subjects performed one-legged dynamic knee-extension. Blood samples were drawn from the femoral artery and vein, and muscle biopsies were obtained from the quadriceps muscle. Leg blood flow was measured by the thermodilution technique, and 3H-inulin was infused for determination of extra- and intracellular muscle water shifts. During the submaximal work load (S) muscle lactate increased, whereas muscle pH remained almost constant; after maximal exercise (M) the values markedly increased for lactate and decreased for pH. Except for a release of lactate from the exercising muscles, K was continuously released throughout S, and this release increased during M. Immediately when the muscles relaxed, the K release was converted to a K re-uptake. The calculated K loss, based on v- a and flow values, agreed with the decrease in muscle K content from 458 mmol/kg dw at rest to 414 mmol/kg dw at exhaustion (P less than 0.05), as analyzed on the muscle biopsies. Muscle water content increased during S mainly because of an increased extracellular H2O, whereas during M the largest increase occurred in intracellular H2O (H2Oi). Because of the simultaneous K loss and H2Oi increase in the exercising muscle the intracellular [K] was calculated to decrease from 165 mM at rest to 129 mM at exhaustion. This decrease and an increase in extracellular [K] from 4.5 mM at rest to greater than 6.0 mM at exhaustion affects the muscle membrane excitability. Muscle fatigue may thus not only be caused by changes within the cell, affecting energy metabolism or actin-myosin reaction, but may be located at the membrane protecting the cell against overload.
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PMID:Water and ion shifts in skeletal muscle of humans with intense dynamic knee extension. 397 Feb 34

Amino acid incorporation into myocardial protein was studied in rats after an acute bout of exhaustive swimming. Hearts were removed at exhaustion, 1, 2, or 4 h of recovery and amino acid incorporation measured using [3H] phenylalanine in an isolated perfused heart preparation. Amino acid incorporation into total tissue protein was reduced 30% at exhaustion but returned to normal by 1 h of recovery and showed no further change 4 h post exercise. In the myofibrillar fraction amino acid incorporation decreased slightly after exhaustive exercise but was stimulated by 57% following 2 h recovery. Myosin, electrophoretically fractionated showed an 84% stimulation in phenylalanine incorporation at exhaustion and 112% increase 2 h post exercise. Amino acid incorporation into myosin light chains (LC1 and LC2) accounted for most of the increased rate of synthesis. These data suggest that there was a preferential increase in myocardial protein synthesis following exercise which was associated with the myosin light chain components of the contractile proteins.
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PMID:Effect of exercise on amino acid incorporation into myocardial contractile proteins. 731 64

The responses of AMP deaminase (AMPD) and branched-chain oxoacid dehydrogenase (BCOAD) to moderate (70% maximal O2 consumption for 90 min) followed by intense (90% maximal O2 consumption to exhaustion) cycling exercise were evaluated in the active skeletal muscle of human subjects (n = 8). The exercise conditions invoke different energy demands and ammonia production rates. Active muscle and plasma ammonia concentrations continuously increased throughout moderate exercise in the absence of significant inosine 5-monophosphate accumulation. The free activity of AMPD decreased during moderate exercise (by approximately 25-35%), whereas myosin-bound activity did not change. BCOAD was significantly dephosphorylated (activated) at 5 min and was continuously dephosphorylated during moderate exercise (to a maximum of approximately 21%). Ammonia accumulation rate increased dramatically during the higher intensity exercise accompanied by inosine monophosphate accumulation of approximately 2 mmol/kg dry muscle. The higher intensity exercise caused no further changes in AMPD activity distribution or BCOAD dephosphorylation. Resting muscle percent bound AMPD was notably higher than values previously reported for rat muscle. Increases in percent bound AMPD during exercise were the result of decreases in the sum of free and bound activities and not increases in bound activity. The results of this study do not support a role for myosin binding in the activation of AMPD in human skeletal muscle.
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PMID:Exercise causes branched-chain oxoacid dehydrogenase dephosphorylation but not AMP deaminase binding. 766 17


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