Glucose phosphorylation is/is not a significant barrier to muscle glucose uptake by the working muscle.
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Animals↗
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Analysis of gene expression differences between utrophin/dystrophin-deficient vs mdx skeletal muscles reveals a specific upregulation of slow muscle genes in limb muscles.
Dystrophin deficiency leads to the progressive muscle wasting disease Duchenne muscular dystrophy (DMD). Dystrophin-deficient mdx mice are characterized by skeletal muscle weakness and degeneration but they appear outwardly normal in contrast to DMD patients. Mice lacking both dystrophin and the dystrophin homolog utrophin [double knockout (dko)] have muscle degeneration similar to mdx mice, but they display clinical features similar to DMD patients. Dko limb muscles also lack postsynaptic membrane folding and display fiber-type abnormalities including an abundance of phenotypically oxidative muscle fibers. Extraocular muscles, which are spared in mdx mice, show a significant pathology in dko mice. In this study, microarray analysis was used to characterize gene expression differences between mdx and dko tibialis anterior and extraocular skeletal muscles in an effort to understand the phenotypic differences between these two dystrophic mouse models. Analysis of gene expression differences showed that upregulation of slow muscle genes specifically characterizes dko limb muscle and suggests that upregulation of these genes may directly account for the more severe phenotype of dko mice. To investigate whether any upregulation of slow genes is retained in vitro, independent of postsynaptic membrane abnormalities, we derived mdx and dko primary myogenic cultures and analyzed the expression of Myh7 and Myl2. Real-time reverse transcriptase-polymerase chain reaction analysis demonstrates that transcription of these slow genes is also upregulated in dko vs mdx myotubes. This data suggests that at least part of the fiber-type abnormality is due directly to the combined absence of utrophin and dystrophin and is not an indirect effect of the postsynaptic membrane abnormalities.
Animals↗
Effects of muscle fatigue induced by low-level clenching on experimental muscle pain and resting jaw muscle activity: gender differences.
The purpose of this study was to investigate the effects of jaw-muscle fatigue evoked by low-level tooth-clenching followed by the induction of experimental muscle pain by injection of glutamate on the perception of fatigue and pain and on the resting electromyographic (EMG) activity. In addition, the role of gender on these interactions was studied. The EMG activities of bilateral masseter (MAL, MAR) and temporalis (TAL, TAR) muscles in 11 healthy young women and 12 men were measured before (Baseline) and after tooth-clenching for 30 min at 10% of maximal force (Post1), after subsequent glutamate (Glu) or isotonic saline (Iso) injection into the MAL following the tooth-clenching (Post2) and 60 min after tooth-clenching (Post3). The intensities of fatigue, fatigue-related muscle pain and headache-like symptoms were scored on 0-10 cm visual analog scales (VAS). The glutamate-evoked pain was continuously scored on an electronic VAS. Sustained low-level tooth-clenching consistently produced fatigue sensation, fatigue-related muscle pain and headache-like symptoms in both genders with significantly higher fatigue VAS scores in men than in women, while the accompanying increase in the resting EMG activity appears higher in women than in men in the masseter muscles. In this study no gender differences were found for the perceived amount of experimental pain induced by glutamate injection. Additional increases of the resting EMG activity after injections occurred only in men in the injected masseter muscle and non-injected temporalis muscles. The present findings provide new information on the complex influence of gender on sensory-motor integration in the trigeminal system which may contribute to differences in susceptibility to develop musculoskeletal pain problems.
Adult↗
Neuronal pathways from group-I and -II muscle afferents innervating hindlimb muscles to motoneurons innervating trunk muscles in low-spinal cats.
Synaptic inputs to motoneurons innervating the back and abdominal muscles in the lumbar part of the body from low-threshold hindlimb muscle afferents were studied in unanesthetized low-spinal cats. At a stimulus intensity of 1.2-1.5x threshold (T), which was sufficient to activate only group-I afferents, the incidence of post-synaptic potentials (PSPs) was higher when stimulating proximal muscle nerves than when stimulating distal muscle nerves (e.g., 52% versus 22% for motoneurons innervating m. iliocostalis lumborum: Ilio MNs; 38% versus 18% for motoneurons innervating m. obliquus externus: OEA MNs). At 2-5 T, at which group-II as well as group-I muscle afferents were presumably stimulated, the PSP incidence increased irrespective of nerves stimulated (e.g., 76% for Ilio MNs; 60% for OEA MNs). The minimal central latencies of EPSPs evoked at 1.2-1.5 T ranged 0.8-16.7 ms for Ilio motoneurons and 1.4 -14.2 ms for OEA motoneurons, indicating that the connection between back and abdominal motoneurons and low-threshold afferents from the hindlimb muscle include a monosynaptic one. The latencies of IPSPs were longer and ranged 1.9-18.8 ms for Ilio motoneurons and 2.4-15.8 ms for OEA motoneurons. Input patterns from various hindlimb muscles varied among individual motoneurons, even though they were within the same motoneuron pool. Such synaptic organization seems to differ from that for the leg motoneuron pool. The overall projection pattern of low-threshold afferents from leg muscles to lumbar back and abdominal motoneurons nevertheless suggests that group-I afferent inputs are related to lateral and vertical movements, and that group-II afferent inputs control the stiffness of the trunk.
Afferent Pathways↗
The influence of muscle length on muscle fibre conduction velocity and development of muscle fatigue.
The influence of muscle (vastus lateralis) length on the muscle fibre conduction velocity (MFCV) and on muscle fatigue was studied in 8 healthy volunteers. In experiment 1, the electromyographic (EMG) responses were evoked by electrical stimulation of the motor point and recorded by a surface electrode array aligned along the muscle fibre direction. The MFCV (determined by cross-correlation) was measured at knee flexions of 5 degrees (full extension), 45 degrees, 90 degrees and 120 degrees with 3 different extension torques. The MFCV declined with increasing muscle length and increased with increasing background torque at knee flexions from 5 degrees to 90 degrees. From 90 degrees to 120 degrees knee flexion of MFCV tended to increase. In experiment 2, the EMG activity at a static fatiguing contraction (80% MVC) was measured at 45 degrees and 90 degrees knee flexion. The EMG was measured until the subject gave up contracting the muscle (endurance). The largest increase in the RMS amplitude and the fastest decreases in the mean power frequency (MPF) and MFCV were found at 90 degrees flexion. The MVC at 45 degrees knee flexion was 35% lower than at 90 degrees and the time until endurance was approximately twice as long for the 45 degrees contraction. The results indicate that muscle length is an important parameter for the propagation velocity of action potentials and for the development of static muscle fatigue.
Action Potentials↗
Muscle fatigue of the elbow flexor muscles during two intermittent exercise protocols with equal mean muscle loading.
OBJECTIVE: Whether different muscle-loading patterns with the same mean load have a similar influence on the resultant muscle fatigue is still unknown. This study investigated the influence of two intermittent exercise protocols, with equal mean muscle loading, on the mechanical and myoelectrical signs of fatigue in the elbow flexor muscles. DESIGN: Ten subjects performed two 20-min long intermittent isometric elbow flexion tasks. The exercise period load for the low force intermittent test was 25% of the maximum voluntary contraction, with a work-cycle time of 20 s and a duty cycle of 0.5. The high force intermittent exercise protocol had an exercise period load of 50% maximum voluntary contraction, a cycle time of 20 s and a duty cycle of 0.25. METHODS: Muscle fatigue was quantified both by measuring the maximal voluntary contraction torque before and after the intermittent exercises, and also by the temporal changes observed in the electromyography signal. RESULTS: Both muscle-loading patterns induced a 15% decrease in maximum voluntary contraction. However, the electromyographic spectral changes during the intermittent static contractions varied between the two protocols. CONCLUSIONS: Variation in muscle load without loss in productivity can affect the physiological responses. The results also showed that different methods to assess muscle fatigue sometimes provide different information on the resultant fatigue.
Adult↗
Changes in muscle fibre type, muscle mass and IGF-I gene expression in rabbit skeletal muscle subjected to stretch.
The relationship between IGF-1 and changes in muscle fibre phenotype in response to 6 d of stretch or disuse of the lower limb muscles of the rabbit was studied by combining in situ hybridisation and immunohistochemistry procedures. Passive stretch by plaster cast immobilisation of the muscle in its lengthened position not only induced an increase in IGF-I mRNA expression within the individual muscle fibres but also an increase in the percentage of fibres expressing neonatal and slow myosin. This change in phenotype was also found to be accompanied by a rapid and marked increase of muscle mass, total RNA content as well as IGF-I gene expression. In contrast, IGF-I appears not to be involved in muscle atrophy induced by immobilisation in the shortened position and the inactivity which results from this procedure. The level of increase in expression of IGF-I mRNA varied from fibre to fibre. By using adjacent serial sections, the fibres which expressed IGF-I mRNA at the highest levels were identified as expressing neonatal and the slow type 1 myosin. These data suggest that the expression of IGF-I within individual muscle fibres is correlated not only with hypertrophy but also with the muscle phenotypic adaptation that results from stretch and overload.
Adaptation, Physiological↗
Muscle atrophy in patients receiving hemodialysis: effects on muscle strength, muscle quality, and physical function.
BACKGROUND: Dialysis patients are less active and have reduced functional capacity compared to individuals with normal renal function. Muscle atrophy and weakness may contribute to these problems. This investigation was undertaken to quantify the extent of atrophy in the lower extremity muscles, to determine whether defects in muscle specific strength (force per unit mass) or central nervous system (CNS) activation are present, and to assess the relationship between muscle size and physical performance in a group of patients on hemodialysis. METHODS: Thirty-eight dialysis subjects (aged 55 +/- 15 years) and nineteen healthy sedentary controls (aged 55 +/- 13 years) were enrolled. Magnetic resonance imaging of the lower leg was used to determine the total cross-sectional area (CSA) and the area of contractile and non-contractile tissue of the ankle dorsiflexor muscles. Isometric dorsiflexor strength was measured during a maximal voluntary contraction with and without superimposed tetanic stimulation (N = 22 for dialysis subjects, N = 12 for controls). Physical activity was measured by accelerometry, and gait speed was recorded as a measure of physical performance. RESULTS: Dialysis subjects were weaker, less active, and walked more slowly than controls. Total muscle compartment CSA was not significantly different between dialysis subjects and controls, but the contractile CSA was smaller in the dialysis patients even after adjustment for age, gender, and physical activity. Central activation and specific strength were normal. Gait speed was correlated with contractile CSA. CONCLUSIONS: Significant atrophy and increased non-contractile tissue are present in the muscle of patients on hemodialysis. The relationship between contractile area and strength is intact in this population. Muscle atrophy is associated with poor physical performance. Thus, interventions to increase physical activity or otherwise address atrophy may improve performance and quality of life.
Adult↗
Comparison of muscle mass preservation in denervated muscle and transplanted muscle flaps after motor and sensory reinnervation and neurotization.
The gracilis muscle model was used either as a denervated muscle in situ or as a transplanted flap in 273 rats to compare the trophic effects of muscle reinnervation and neurotization using sensory and motor nerves. The average gracilis muscle flap weighed 626 +/- 94 mg at the time of the initial procedure. Experimental muscles were examined 6 months following the procedure. In denervated, nontransplanted muscles, both motor nerve reinnervation and neurotization resulted in significantly preserved muscle mass, averaging 570 +/- 69 and 521 +/- 116 mg, respectively, compared with the denervated control average of 178 +/- 22 mg (p < 0.05). Sensory nerve reinnervation and neurotization produced much smaller trophic effects (p > 0.05). In transplanted gracilis free flaps, however, only direct reinnervation with motor or sensory nerves resulted in improved bulk preservation, with average weights of 313 +/- 83 and 327 +/- 91 mg compared with the control average of 201 +/- 76 mg (p < 0.05). Neither sensory nor motor neurotization was significantly effective in the free-flap model (p > 0.05). These data suggest that transplantation may alter the response of muscle to reinnervation.
Animals↗
The influence of inspiratory muscle work history and specific inspiratory muscle training upon human limb muscle fatigue.
The purpose of this study was to assess the influence of the work history of the inspiratory muscles upon the fatigue characteristics of the plantar flexors (PF). We hypothesized that under conditions where the inspiratory muscle metaboreflex has been elicited, PF fatigue would be hastened due to peripheral vasoconstriction. Eight volunteers undertook seven test conditions, two of which followed 4 week of inspiratory muscle training (IMT). The inspiratory metaboreflex was induced by inspiring against a calibrated flow resistor. We measured torque and EMG during isometric PF exercise at 85% of maximal voluntary contraction (MVC) torque. Supramaximal twitches were superimposed upon MVC efforts at 1 min intervals (MVC(TI)); twitch interpolation assessed the level of central activation. PF was terminated (T(lim)) when MVC(TI) was <50% of baseline MVC. PF T(lim) was significantly shorter than control (9.93 +/- 1.95 min) in the presence of a leg cuff inflated to 140 mmHg (4.89 +/- 1.78 min; P = 0.006), as well as when PF was preceded immediately by fatiguing inspiratory muscle work (6.28 +/- 2.24 min; P = 0.009). Resting the inspiratory muscles for 30 min restored the PF T(lim) to control. After 4 weeks, IMT, inspiratory muscle work at the same absolute intensity did not influence PF T(lim), but T(lim) was significantly shorter at the same relative intensity. The data are the first to provide evidence that the inspiratory muscle metaboreflex accelerates the rate of calf fatigue during PF, and that IMT attenuates this effect.
Adaptation, Physiological↗
Isolation of camel brain actin--comparison of its biochemical properties with those of camel skeletal muscle, heart muscle and rabbit skeletal muscle actins.
1. Actins were purified from camel brain, skeletal muscle and heart muscle and their properties were compared. 2. Individual actins were homogeneous and comigrated on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). 3. Isoelectric focusing analysis of camel skeletal muscle and heart muscle actin showed a single polypeptide of the alpha-species, while camel brain actin showed two polypeptides of the beta- and gamma-species typical of non-muscle actin. 4. Actins from camel skeletal muscle and heart muscle showed a greater degree of similarity to each other and to rabbit skeletal muscle actin and showed some differences from camel brain actin, as confirmed by amino acid analysis and one-dimensional peptide mapping.
Actins↗
Binding of -bungarotoxin to acetylcholine receptors in mammalian muscle (snake venom-denervated muscle-neonatal muscle-rat diaphragm-SDS-polyacrylamide gel electrophoresis).
Experiments were performed to determine the specificity of [(125)I]alpha-bungarotoxin binding to skeletal muscle. In adult rat diaphragm, [(125)I]alpha-bungarotoxin was found to bind almost exclusively to those regions of the muscle that contain endplates and are known to be sensitive to acetylcholine. In contrast, chronically denervated adult muscle and muscle from neonatal rats, both of which are sensitive along their entire lengths, bound substantial amounts of toxin in all regions. Toxin binding to all muscles was inhibited by d-tubocurarine and by carbamylcholine, but not by atropine. The bound [(125)I]toxin was solubilized by homogenization of the tissue in 1% Triton X-100 and was recovered as a single band, distinct from free toxin, after zone sedimentation. Treatment of the solubilized, toxin-bound complex with 2-mercaptoethanol and sodium dodecyl sulfate resulted in the recovery of free toxin. A toxin-bound complex was also obtained when toxin was incubated directly with extracts of muscle endplate regions prepared by homogenization in Triton X-100. No such complex was observed with extracts prepared from muscle lacking endplates. These results are consistent with the interpretation that alpha-bungarotoxin binds specifically to the acetylcholine receptor of mammalian skeletal muscle.
Acrylamides↗
Defects in neuromuscular junction structure in dystrophic muscle are corrected by expression of a NOS transgene in dystrophin-deficient muscles, but not in muscles lacking alpha- and beta1-syntrophins.
Muscular dystrophies that arise from mutations of genes that encode proteins in the dystrophin-glycoprotein complex (DGC) frequently involve defects in the structure of neuromuscular junctions (NMJs). DGC mutations that cause NMJ defects typically cause a secondary loss of neuronal nitric oxide synthase (nNOS) from the post-synaptic membrane. We tested the hypothesis that reduction of muscle-derived NO production causes NMJ defects in DGC mutants by analyzing the effect of modulating muscle NO production on NMJ structure in mutant and wild-type muscles. We found that nNOS null mutants, dystrophin-deficient mdx mice and alpha-syntrophin null mutants showed reductions in the concentration of acetylcholine receptors (AChRs) at the post-synaptic membrane. Also, expression of a muscle-specific NOS transgene increased AChR concentration, which reflected an increase in both AChR expression and clustering. NOS transgene expression also increased the size of NMJs, and partially corrected defects in normal NMJ architecture that were observed in mdx and alpha-syntrophin null muscles. In addition, stimulation of AChR clustering in vitro by application of laminin or VVA B4 lectin induced a 3-4-fold increase in NOS activity and increased AChR clustering that could be prevented by NOS inhibition. However, the partial rescue of NMJ structure by expression of a NOS transgene required the expression of alpha- or beta1-syntrophin at the NMJ; partial NMJ rescue was seen in the muscles of alpha-syntrophin mutants that expressed beta1-syntrophin, but no rescue was observed in muscles of alpha-syntrophin mutants that also lacked beta1-syntrophin. These findings show that NO promotes AChR expression and clustering in vivo and contributes to normal NMJ architecture. The results suggest that defects in NMJ structure that occur in some DGC mutants can result from the secondary loss of NOS from muscle.
Animals↗
Muscle fibre type and size, and muscle capillary density in young double-muscled blue Belgian cattle.
Bovine muscle biopsies were analysed for fiber type and capillary density by the acid ATP-ase and amylase-PAS methods respectively. Samples obtained from Belgian blue double muscled (DM) calves were compared for their fibre type, size and vascularization with samples from Friesian (F) calves. The animals were sampled both at 2 and 7 months of age. Changes in histochemical composition occurring with ageing, independently of the breed, and differences related to the muscle sampled by comparing biopsies obtained from the longissimus dorsi (LD) and gluteobiceps (GB) muscles in animals of both breed were also investigated. Independently of age and muscle, fibre type I percentage and area were significantly higher in F than in DM muscles. Type IIa area was significantly larger in F than in DM, while fibre type IIb percentage and area were higher in DM. The number of capillaries/mm2 was significantly higher in F than in DM. Fibre type IIa and IIb percentage as well as the diameter of the three fibre types was significantly higher in the oldest animals. Finally, independently of age and breed, fibre type I and IIb percentages were significantly higher in LD but lower in GB. The results mainly demonstrated that Belgian blue DM muscles present a higher proportion of IIb fibres and a lower capillary supply than F muscles.
Animals↗
Glycolytic enzyme profiles in the arrector pili muscle and the subcutaneous muscle. Comparison between smooth and skeletal muscle. Comparison between smooth and skeletal muscle.
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Adenosine Triphosphatases↗
Role of patellar tendon on the population of muscle fiber types and the contractile properties of single glycerinated muscle fibers in quadriceps muscles of rats.
The role of the patellar tendon (PT) in the contractile properties of quadriceps muscle was investigated. After PT resection (partial or complete), PT reconstruction, or a sham operation, rats were forced to run on a rodent treadmill. The histochemical and mechanical characteristics of the vastus medialis (VM) and vastus lateralis (VL) muscles were examined 2, 4, and 8 weeks after treatment. There were no significant changes in either fiber type population or the contractile properties of glycerinated single muscle fibers from VM and VL 2 and 4 weeks after partial PT resection. Complete PT resection caused a decrease in the population of type I fibers in VM, while the running training after PT reconstruction increased the population of type I fibers in VM. For both the PT resection and PT reconstruction groups, the Hill coefficient, an indicator of the Ca2+ sensitivity of myofilaments, was calculated from the pCa-tension relationship of glycerinated single muscle fibers. In the PT reconstruction group, the Hill values for fibers isolated from VM were significantly decreased by running training, but the Hill values for VL were not. The effect of running training on the Ca2+ sensitivity of myofilaments in muscle fibers with PT reconstruction was different from that in muscle fibers without PT treatment. Both resection and partial resection of the PT in this animal model had heterogeneous effects on the contractile properties of quadriceps muscles; we presume that, clinically, we must give careful consideration to PT treatment.
Animals↗
Bilateral variations of the psoas major and the iliacus muscles and presence of an undescribed variant muscle--accessory iliopsoas muscle.
Inspite of the detailed description of the iliopsoas muscle complex, interesting variations of its main parts--the psoas major and the iliacus muscles can still be encountered. These variations may clarify some aspects of the embryological development of the iliopsoas and have certain clinical importance because of the frequent co-existence with an unusual femoral nerve by its formation and course. We present in our report a case of bilateral variations of the psoas major and the iliacus muscles combined with variations of the left and the right femoral nerves, which were found during the anatomical dissection of a female human cadaver. The most remarkable finding was noted on the left side, where an undescribed variant muscle accessory iliopsoas, was observed. It was the only finding of such a muscle among 108 human cadavers examined over a period of 22 years. The accessory iliopsoas was formed by the connection of two accessory muscles--accessory psoas major and accessory iliacus. The clinical significance of the described variant muscles and their importance as an additional factor in the femoral neuropathy are also a matter of discussion in our report.
Aged↗
Turnover rates of muscle protein in cardiac and skeletal muscles of dog, fowl, rat and mouse: turnover rate related to muscle function.
Turnover rates of muscle protein in cardiac and skeletal muscle have been measured in dogs using a continuous infusion of 14C-tyrosine, and in fowls, rats and mice after a pulse label of either 3H-leucine or 3H-aspartate. In all species the total mixed protein from ventricle turned over the most rapidly. Tonic muscles predominantly comprised of red fibres were intermediate in rate and twitch muscles comprised of predominantly white fibres had the slowest rates of turnover. This same progression of turnover rates was also seen in myofibrillar and sarcoplasmic protein fractions and with myosin. The RNA concentrations of the muscle tissue were highly correlated with the turnover rates. It is suggested that the turnover rate of muscle protein is related to the function of the muscle.
Animals↗