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

Earlier studies had failed to show the presence of capillaries between the white fibres of pigeon pectoralis muscle. In this paper, data are reported for the first time documenting that these capillaries occur in both intra- and inter-fasicular areas of the muscle. Fresh frozen sections of pigeon pectoralis major muscle were incubated for alkaline ATPase reaction following pretreatment with different EDTA solutions (4.3 mM, pH 4.3). The results showed the existence of an inherent heterogeneity of capillaries. The capillaries of white fibres stained intensely for K+/Mg2+-EDTA or Mg2+-EDTA pre-incubated ATPase; the capillaries of red fibres stained poorly. Both white fibre and red fibre capillaries were examined ultrastructurally in the non-perfused pigeon pectoralis muscle. It is suggested that a possible correlation exists between the distinctive metabolic and mechanical characteristics of the Type II white, glycolytic, fast-twitch fast-fatigue muscle fibres and the high ATPase activity of their capillaries.
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PMID:On the heterogeneity of capillaries of pigeon pectoralis muscle: a histoenzymatic and ultrastructural study. 15 80

1. A diffuse-conducting system close to the dorsal epithelium of the polyclad flatworm Freemania litoricola is described. Tactile stimuli elicit small action potentials which can be conducted around lesions through the body wall. The potentials can occur in bursts or barrages. 2. This conducting system appears to be insensitive to Mg2+ ions. 3. Conduction velocities (0-26--71 m/sec) vary over the animal. Conduction spread in the anterior half of the animal appears to be greater than that in the posterior portion. 4. Response decrement to repeated stimulation can be recorded in the peripheral system but it is not clear if this is due to habituation or fatigue. 5. Conduction from the peripheral net to the brain occurs. Some central units appear to pick up information only, or mainly, through the anterior nerves, while other units can respond to information conducted through the network to nerves of the contralateral side. 6. Different possibilities to account for this system are discussed, and it is suggested that the animals either possess a unique Mg2+ insensitive synaptic nerve-net or else the network is electrically coupled.
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PMID:Electrophysiology of the peripheral nerve net in the polyclad flatworm Freemania litoricola. 120 42

Intracellular free Mg2+ concentration ([Mg2+]i) was measured in isolated single fibres of Xenopus muscle using the fluorescent Mg2+ indicator furaptra. In resting muscle the [Mg2+]i was 1.7 mM in a Mg(2+)-free Ringer solution. There was no significant change in [Mg2+]i over 2 h in Mg(2+)-free Ringer solution. Elevating extracellular [Mg2+] to 40 mM for 5 min caused a small rise (0.13 mM) in [Mg2+]i. There was no detectable rise in [Mg2+]i after 5 min in Na(+)-free Ringer solution. These results suggest that the membrane is relatively impermeable to Mg2+ and that there was no detectable Na(+)-Mg2+ exchange over 5 min. When muscle fibres were fatigued by repeated tetani continued until force declined to about 40% of control, [Mg2+]i showed characteristic changes. During the early period of fatigue when force first showed a small decline and then became almost stable, [Mg2+]i was unchanged; during the final period of fatigue when force declined more rapidly, [Mg2+]i increased by 0.8 mM. Recovery of [Mg2+]i took about 30 min. Recovery of force was complex: tetanic force first declined (post-contractile depression) and then slowly recovered to control. Since the minimum force occurred at about the time when [Mg2+]i had recovered, it seems unlikely that post-contractile depression is caused by elevated [Mg2+]i. Rigor, produced by inhibiting oxidative phosphorylation and glycolysis, was associated with a larger increase (1.6 mM) in [Mg2+]i than fatigue. The rise in [Mg2+]i during fatigue and metabolic blockade could be explained as release of Mg2+ normally bound to ATP. A model of the metabolic changes and the resulting increase in [Mg2+]i explains our results reasonably well.
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PMID:Myoplasmic Mg2+ concentration in Xenopus muscle fibres at rest, during fatigue and during metabolic blockade. 141 55

1. The role of the myoplasmic free Mg2+ concentration ([Mg2+]i) in fatigue was studied in intact single fibres isolated from mouse skeletal muscle. Fatigue was produced by repeated tetanic stimulation. The fluorescent Mg2+ indicator furaptra was pressure injected into fibres. In vivo calibrations were performed to convert fluorescence signals into [Mg2+]i. 2. [Mg2+]i at rest was 0.78 +/- 0.05 mM (mean +/- S.E.M., n = 14). An increase of the extracellular [Mg2+] from 0.5 to 20 mM resulted in a small elevation of [Mg2+]i (86 microM in 5 min). Removal of extracellular Na+ did not affect [Mg2+]i. An intracellular alkanization of about 0.6 pH units gave a [Mg2+]i reduction of 65 microM. 3. During fatiguing stimulation [Mg2+]i initially remained almost constant and it then suddenly started to rise towards the end of the stimulation period. The onset of the [Mg2+]i rise was always followed by a rapid tension decline. In fatigue [Mg2+]i was approximately twice as high as at rest. 4. Fibres were injected with MgCl2 to study if the rise in [Mg2+]i could explain the tension decline in fatigue. An elevation of [Mg2+]i was accompanied by a tension reduction but the [Mg2+]i for a given tension was generally much higher in rested fibres injected with MgCl2 than in fatigued fibres. Thus the rise in [Mg2+]i as such cannot explain the tension reduction in fatigue. 5. Injection of MgCl2 was also used to assess the intracellular Mg2+ buffering. The mean Mg2+ buffer power (i.e. the ratio of the change in [Mg2+]i to the amount of Mg2+ added) was 0.62. 6. ATP is the quantitatively most important binding site for Mg2+ at rest and ATP breakdown is then a likely source of the [Mg2+]i increase in fatigue. The role of ATP breakdown in the increase of [Mg2+]i was studied with metabolic inhibition: fibres were exposed to iodoacetic acid to inhibit glycolysis and cyanide to inhibit oxidative phosphorylation. The pattern during metabolic inhibition was similar to that observed during fatigue. After remaining almost constant during a lengthy period, [Mg2+]i rose rapidly and this rise preceded a period of rapid tension decline. The fibres thereafter went into rigor and [Mg2+]i stabilized at an elevated level; the mean [Mg2+]i increase in rigor was 1.30 mM. 7. We have used modelling to determine the likely change in the intracellular ATP concentration ([ATP]i) for the observed changes in [Mg2+]i.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Myoplasmic free Mg2+ concentration during repetitive stimulation of single fibres from mouse skeletal muscle. 146 36

A material containing only photosystem I (PSI) and the chlorophyll-a/b-binding light-harvesting complex of PSII (LHC-II) has been isolated from the chloroplast thylakoid membrane by solubilization with Triton X-100. Fluorescence spectroscopy shows that, within the material, LHC-II is coupled to PSI for excitation-energy transfer and that this coupling is decreased by the presence of Mg2+, which also decreased PSI electron transport specifically at limiting light intensity. Inclusion of phosphorylated LHC-II within the material did not alter its structure, but gave decreased energy transfer to PSI and inhibition of electron transport which was independent of light intensity, implying effects of phosphorylation on both light harvesting and directly on electron transport. Inclusion of Mg2+ within the phosphorylated material gave decreased energy transfer, but slightly increased PSI electron transport. A cation-induced direct promotion of PSI electron transport was also observed in isolated PSI particles. The PSI/LHC-II material represents a model system for examining protein interactions during light-state adaptations and the possibility that LHC-II can contribute to the antenna of PSI in light state 2 in vivo is discussed.
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PMID:Protein phosphorylation and Mg2+ influence light harvesting and electron transport in chloroplast thylakoid membrane material containing only the chlorophyll-a/b-binding light-harvesting complex of photosystem II and photosystem I. 155 90

1. Transmitter release at neuromuscular junctions of extensor digitorum longus (EDL) muscle in mice was studied after 2-8 month periods of unforced running in wheels. 2. Intracellular recordings at 10 Hz stimulation revealed that the quantal content of endplate potentials (EPPs) in Mg(2+)-blocked preparations was larger by 30% in trained (mean number of quanta, m = 1.75 +/- 0.19, n = 7) than in untrained control EDL muscles (m = 1.35 +/- 0.35, n = 7). Similarly the amplitudes of the first, maximum and plateau EPPs during tetanic stimulation (100 Hz for 1 s or 400 ms) in curare-blocked preparations were increased by 28% each; muscle fibre diameters did not differ while other postsynaptic effects were not excluded. 3. Training effects became particularly evident in two pairs of monozygotic twins, in which the time courses of facilitation and depression were changed as well: at 100 Hz stimulation the maximum EPP amplitude was reached on average at 2.6 impulses in controls but at 2.0 impulses in runners, and the following decline below the value of the first EPP at 5.0 and 3.8 impulses respectively. 4. Block resistance, as monitored by isometric tension measurements in different presynaptic (Mg2+) and postsynaptic (curare) blocking solutions, was higher in trained than in control EDL muscles. Depression in a train of four nerve-evoked single twitches at 2 Hz was lower. 5. As expected from the unchanged fibre diameters (see above) isometric tetanic force was similar in trained and control EDL muscles. Muscle fatigue resistance was larger in trained animals and succinic dehydrogenase activity was higher in fibres of trained muscles indicating an endurance training of the EDL muscle. 6. It is concluded that besides changes in muscle fibre properties, prolonged elevated activity causes increased transmitter release in EDL muscles. As a consequence, the safety margin of transmission in trained EDL muscles is markedly elevated.
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PMID:Effects of enhanced activity on synaptic transmission in mouse extensor digitorum longus muscle. 164 30

The effects of N-methyl-D-aspartate (NMDA) on the free intracellular Ca2+ concentration [( Ca2+]i) and the energy state in superfused cerebral cortical slices have been studied using 19F- and 31P-nuclear magnetic resonance spectroscopy. [Ca2+]i was measured using the calcium indicator 1,2-bis(2-amino-5-fluorophenoxy)ethane-N,N,N',N'-tetraacetic acid (5FBAPTA). NMDA (10 microM) in the absence of extracellular Mg2+ caused the expected rise in [Ca2+]i but produced an impairment of the energy state: the phosphocreatine (PCr) content was decreased by 42%, and the Pi/PCr ratio was increased by 55%. There was no detectable change in ATP or free intracellular Mg2+ concentration. Increasing the NMDA concentration in the superfusing medium to 100 or 400 microM caused no further increase in [Ca2+]i or further decrease in PCr content, but the Pi/PCr ratio continued to rise. The impairment of the energy state preceded the effect on [Ca2+]i, and these changes were irreversible on return to control conditions. Repeating the experiments in the presence of 1.2 mM extracellular Mg2+ resulted in similar changes in the energy state, with no change in [Ca2+]i. The possibilities that the effects were due to membrane depolarisation or to the presence of 5FBAPTA within the tissues were eliminated. The results suggest that low concentrations (10 microM) of NMDA produce an impaired energy state independent of the presence of extracellular Mg2+ and that the decreased energy state is not due to the changes in [Ca2+]i, which are seen only in the absence of extracellular Mg2+.
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PMID:Effects of N-methyl-D-aspartate on [Ca2+]i and the energy state in the brain by 19F- and 31P-nuclear magnetic resonance spectroscopy. 220 83

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

Mg deficiency is a frequent complication of inflammatory bowel disease (IBD) demonstrated in 13-88% of patients. Decreased oral intake, malabsorption and increased intestinal losses are the major causes of Mg deficiency. The complications of Mg deficiency include: cramps, bone pain, delirium, acute crises of tetany, fatigue, depression, cardiac abnormalities, urolithiasis, impaired healing and colonic motility disorders. Serum Mg is an insensitive index of Mg status in IBD. Twenty-four-hour urinary excretion of Mg is a sensitive index and should be monitored periodically. Parenteral Mg requirements in patients with IBD are at least 120 mg/day or more depending upon fecal or stomal losses. Oral requirements may be as great as 700 mg/day depending on the severity of malabsorption.
Magnesium 1988
PMID:Magnesium and inflammatory bowel disease. 329 19

The present study examined the relationships between changes in intra- and extracellular concentrations of strong ions, the appearance of nonvolatile acid (NVA) in venous perfusate, and skeletal muscle fatigue during intense electrical stimulation. A one-pass system was used to perfuse an isolated rat hindlimb during 5 min of intermittent tetanic contractions. Initial isometric tensions averaged 2.85 kg/hindlimb and declined by 45% during 5 min. During stimulation, intracellular lactate concentration ([La-]i) increased by 2, 13, 15, and 21 meq/l of intracellular fluid in the soleus, plantaris, and red and white gastrocnemius. This was associated with a proportionate decrease in intracellular K+ ([K+]i) and Mg2+([Mg2+]i) concentrations and increased intracellular Na+ ([Na+]i) and Cl-([Cl-]i) concentrations. A stoichiometrically equivalent uptake of Na+ and Cl- from the perfusate peaked at 8.5 mu eq.min-1.g-1 at the end of the 5th min. The increase in plasma [K+] during the last 4 min of stimulation was constant at 0.5 mu eq.min-1.g-1. A significant reduction in intracellular strong ion difference of all muscles contributed directly to an increase in [H+] during stimulation. After the 1st min of stimulation the rate of appearance of NVA in venous perfusate exceeded that of the increase in venous plasma [La-] by 12-fold; this decreased to 2.7-fold at the end of 5 min. La- release and NVA appearance in venous perfusate was maximal at 3.1 and 9.7 mu eq.min-1.g wet wt-1 during the 4th min of stimulation. It is concluded that the changes in the intracellular concentrations of strong ions during intense contractile activity are the primary factors contributing to skeletal muscle fatigue.
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PMID:Ion fluxes during tetanic stimulation in isolated perfused rat hindlimb. 333 65


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