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Query: UMLS:C0231530 (twitching)
 2,043 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The imposition of long-term lengthened immobilization on rabbit tibialis anterior (TA) muscles resulted in rapid increases in slow oxidative (SO) fibre number. After 2 weeks, SO number had increased 2-fold and was 5 times greater after 6 weeks immobilization. There were also fibre-type-specific effects on SO, fast oxidative glycolytic (FOG) and fast glycolytic (FG) fibre areas. Twitch strength was unchanged throughout immobilization whilst production of tetanic tension was impaired during the initial period but had returned to control levels by 6 weeks. Twitch contraction times and isometrically determined rates of rise and relaxation were largely unaffected by immobilization despite the marked increase in expression of slow myosin. The change in phenotypic expression of the lengthened TA was not attributable to chronically increased levels of activation since integrated EMG activity was unchanged from control values throughout the immobilization period. Thus it is suggested that a chronic increase in tension consequent on the lengthening procedure is a potent stimulus for fast-to-slow myosin transformation.
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PMID:Effects of lengthened immobilization on functional and histochemical properties of rabbit tibialis anterior muscle. 163 53

1. A mesodermal stem cell line C3H10T1/2 was induced to differentiate to muscle by adding 0.3 microM-5-aza-2'-deoxy-cytidine to the medium for 24 h. The changes in membrane currents during differentiation were studied by whole-cell recording and changes in the expression of fibronectin, Neural Cell Adhesion Molecule (NCAM), myosin and desmin were studied immunohistochemically. 2. The stem cells showed the morphology of fibroblastic cells. Most of the stem cells showed ATP-induced slow K+ current. T-type Ca2+ current and inward rectifier K+ current were observed in 19% of the stem cells. The stem cells expressed fibronectin, but not NCAM, myosin or desmin. 3. About 2 weeks after the addition of 5-aza-2'-deoxy-cytidine, large multinucleated skeletal muscle-like cells appeared. Most of the induced muscles showed L-type Ca2+ current, responses to acetylcholine, outward K+ current, inward rectifier K+ current and contraction upon depolarizing stimulation. They expressed NCAM, myosin and desmin, but not fibronectin, and showed no ATP response. 4. In some batches (2/14), the induced muscles showed spontaneous twitches, and possessed tetrodotoxin (TTX)-sensitive Na+ current in addition to the currents described above. Furthermore clear striation was observed in some of the twitching muscles under Nomarski optics. 5. To ascertain the properties of cells at the initial step of muscle differentiation, whose differentiation is determined but not yet evident morphologically or electrophysiologically, subcloning was performed from the heterogeneous cells 10 days after induction. Three myogenic clones were obtained, which proliferated at low cell densities but differentiated to muscle with a high incidence at high cell densities, as well as ten non-myogenic clones. 6. Most myogenic clones still showed ATP-induced K+ current and fibronectin. In addition, most of them showed T-type Ca2+ current and inward rectifier K+ current. They had already expressed NCAM. No other properties observed in muscles had yet been expressed. Most cells of the non-myogenic clones showed ATP-induced K+ current and fibronectin. T-type Ca2+ current was also expressed, but not inward rectifier K+ current or NCAM. 7. The properties of the observed ionic currents were studied. The TTX-sensitive Na+ current could be completely blocked by 0.1 microM-TTX. It could be evoked by depolarizing steps to a level above -40 mV, while steady-state inactivation was detectable around -75 mV and reached half by -52 mV. T-type Ca2+ current could be evoked by a depolarizing pulse to a level above -45 mV, with a maximum amplitude around -15 mV.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Electrophysiological and immunohistochemical analysis of muscle differentiation in a mouse mesodermal stem cell line. 166 64

The influence of the thyroid gland on the functional and histochemical development of fast- and slow-twitch skeletal muscle of fetal sheep has been studied in euthyroid fetal sheep (n = 6) and athyroid fetuses (n = 4) surgically thyroid-ectomized at 70-75 days of gestation. Two fast-twitch muscles, the medial gastrocnemius and extensor digitorum longus, and the slow-twitch soleus muscle were studied at the fetal age of 140 days gestation. The athyroid fetuses had significantly slower twitch contraction and relaxation times in both the medial gastrocnemius and extensor digitorum longus muscles compared with the euthyroid fetuses. Twitch contraction and relaxation times of the soleus were not different in the two groups. Thyroidectomy resulted in an increase in the proportion of fast (type II) muscle fibers and myosin, as shown histochemically and by gel electrophoresis of heavy-chain myosins. These results indicate that the functional maturation of the fast-twitch muscles of sheep is influenced by the presence of an intact thyroid gland from at least 70 days of gestation. In contrast, the slow-twitch soleus muscle fiber diameter and twitch contraction and relaxation times were not different in the two groups.
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PMID:Effects of thyroidectomy on development of skeletal muscle in fetal sheep. 195 79

Samples taken from the middle gluteal muscle of 95 untrained adult horses of different ages and sex were subjected to histochemical analysis using the myosin adenosine triphosphatase (m-ATPase) and nicotinamide adenine dinucleotide tetrazolium reductase (NADH-TR) staining techniques. Fibres were classified into types I, IIA and IIB according to m-ATPase activity after preincubation at pH 4.4. The percentage of FT (Fast-Twitch Glycolytic) fibres and the proportion of IIB fibres with "high" and "low" oxidative capacity were determined in serial sections stained for NADH-TR. Statistical analysis revealed a significantly higher proportion of IIB fibres than FT fibres (P less than 0.001), though both percentages were correlated. Thus, 72.2 +/- 17.6% of type IIB fibres showed low oxidative capacity, but the remaining 27.8 +/- 17.6% showed high aerobic potential, and thus did not correspond to FT fibres. These results confirm that the contractile capacity of a muscle fibre does not determine its oxidative profile. The different types of muscle fibre should thus be classified solely according to m-ATPase activity, since this characteristic is related to the molecular structure of contractile proteins. Oxidative capacity should be assessed separately, and not be used as a criterion for fibre classification in horses.
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PMID:Degree of correspondence between contractile and oxidative capacities in horse muscle fibres: a histochemical study. 215 81

Twitch tension and phosphate incorporation into the phosphorylatable light chains (P-light chains) of myosin were studied during a 10-min recovery period following a 10- or 60-s maximal voluntary isometric contraction (MVC) in 18 subjects. Analysis of muscle biopsy samples obtained before, immediately after, 1 min, and 10 min following the 10-s MVC revealed that the 10-s MVC produced a modest but transient metabolic displacement from rest, a 35% decrease in phosphocreatine, and a threefold elevation in lactate concentration. Immediately after the 60-s MVC, ATP was decreased by 20%, phosphocreatine decreased by 84%, and lactate was elevated by 15-fold. Lactate remained elevated over the 10-min recovery period. Twitch force was maximally potentiated following the 10-s MVC and declined to rest by 10 min of recovery. Twitch force was 0.66 of rest value immediately after the 60-s MVC, then increased over the next 4 min to reach a potentiated value 21% greater than rest, before declining. Significant phosphate incorporation into P-light chains was observed immediately after both contractions, but dephosphorylation to rest values at the end of recovery was only noted for the 60-s condition. These results demonstrate an inconsistent relationship between twitch tension enhancement and P-light chain phosphorylation in the in vivo human model.
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PMID:Myosin phosphorylation, twitch potentiation, and fatigue in human skeletal muscle. 238 4

To examine how different kinds of activity affect the composition and contractile properties of aging skeletal muscle, old male rats were strength and swim trained. The mass of weights lifted during the strength training increased by 85 +/- 9% (P less than 0.05), which was accompanied by an increase by 32 +/- 5% (P less than 0.05) of the estimated force developed. The wet muscle weight of the soleus and the plantaris decreased significantly with age. The phenomenon was counteracted but not neutralized by the strength training. Twitch and tetanic tension also decreased significantly with age in both the soleus and plantaris muscle. This was avoided by the strength training. This training also significantly decreased time to peak tension and half-relaxation time of both muscles. The swim training increased the heart-to-body weight ratio by 21 +/- 5% (P less than 0.05) and the endurance of the soleus muscle. Time to peak tension and triosephosphate dehydrogenase activity of the plantaris muscle were strongly correlated (P less than 0.001) with myosin adenosinetriphosphatase activity. The results show that the composition and contractile properties of old skeletal muscle are considerably affected by strength training repeated during a substantial period of old age, whereas swim training only affects the endurance of the skeletal muscle.
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PMID:Contractile properties of old rat muscles: effect of increased use. 252 39

The effects of hypothyroidism on structural and functional properties of the actomyosin-ATPase complex of rat fast-twitch gastrocnemius muscle were examined and related to energetic and mechanical parameters. Hypothyroidism resulted in the appearance of a small band of the myosin heavy chain subunit of the slow form (MHCs) 8% of total MHC) which was absent in the euthyroid group. This observation corresponded with lower activities of myofibrillar ATPase (-14%) and Ca-activated myosin ATPase (-9%) in the hypothyroid group, although these changes were not significant. No effect of hypothyroidism on the Ca2+-sensitivity of the myofibrillar-ATPase activity was observed and tetanic force was not changed. Twitch force, however, was significantly increased by hypothyroidism. The degree of myosin P-light chain phosphorylation (percentage of total amount of P-light chain) determined after 5 and 10 s of tetanic stimulation (130 Hz, 35 degrees C), respectively, proved to be significantly lower in the hypothyroid group (5 s: 57%; 10 s: 61%) vs the euthyroid group (5 s: 79%; 10 s: 82%). There was no difference in P-light chain phosphorylation at rest between eu- and hypothyroids. The results suggest that a decreased actomyosin-ATPase activity can only in part contribute to the 30% lower energy turnover during force development found for fast-twitch skeletal muscle of hypothyroid rats. Moreover, the increase in twitch force by hypothyroidism cannot be explained by a change in myosin P-light chain phosphorylation. Isometric twitch tension potentiation after a 2 s tetanus and during low-frequency repetitive stimulation was reduced (up to -60%) in muscles of hypothyroid rats, which may well be related to the lower extent of P-light chain phosphorylation in hypothyroids.
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PMID:Structural and functional aspects of the actomyosin complex from fast-twitch muscle of euthyroid and hypothyroid rats. 296 Sep 52

Spontaneous release of neurotransmitter has been demonstrated in various types of synapses. Its physiological significance, however, is still unknown. In nerve-muscle cultures of embryonic Xenopus laevis, we observed that acetylcholine, which is released spontaneously at the synaptic terminal, caused frequent twitches of muscle cells. These muscle cells developed cross-striations earlier than neighboring non-twitching cells. This effect of innervation was unaffected by tetrodotoxin but was blocked by alpha-bungarotoxin. Repeated iontophoretic application of acetylcholine or KCl to muscle cells caused twitches and also accelerated the formation of cross-striations. Thus twitching apparently promotes lateral alignment of myofibrils. It is also known that myosin synthesis is higher in twitching muscle cells. Therefore, successfully innervated twitching muscle cells may have an advantage for faster differentiation over neighboring non-twitching muscle cells. We suggest that spontaneously released transmitter may serve as a mediator for trophic interaction at forming synapses.
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PMID:Early cross-striation formation in twitching Xenopus myocytes in culture. 327 23

Serial sections of stage 18-27 HH (3-5 days of incubation) chick embryo myotomes were investigated by electron microscope. Two morphologically different types of contractile elements (myoblasts and myotubes) with an exact and constant localization were identified. Myotome sections of other chick embryos in the same stages were examined with the immunofluorescence technique, after treatment with antisera directed against fast and slow adult myosins. As from stage 24 HH, some contractile elements react positively with anti-fast adult myosin antiserum, others with anti-slow antiserum. A very precise correspondence was constantly found between the ultrastructural and immunohistochemical findings. An identical pattern was observed in the buds of the fast-twitching pectoralis major and posterior latissimus dorsi and slow-twitching anterior latissimus dorsi muscles.
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PMID:Early myoblast differentiation in fast and slow types. 329 25

Twitch tension and maximal unloaded velocity of human knee extensor muscles were studied under conditions of low phosphate content of the phosphorylatable light chains (P-light chains) of myosin and elevated phosphate content, following a 10-s maximal voluntary isometric contraction (MVC). After the MVC, twitch tension was significantly potentiated, with greater potentiation observed at a shorter muscle length (p less than 0.05). The MVC was associated with at least a twofold increase in phosphate content of the fast (LC2F) and two slow (LC2S and LC2S') P-light chains, but this increase was unrelated to muscle length. No significant differences in knee extension velocity were observed between conditions where P-light chains had low or elevated phosphate content. Positive but nonsignificant correlations were noted between the extent of twitch potentiation and phosphate content of individual P-light chains as well as the percentage of type II muscle fibres in vastus lateralis muscle. No significant relationships were determined for myosin light chain kinase activity and either P-light chain phosphorylation or type II fibre percentage. These data suggest that, unlike other mammalian fast muscles, P-light chain phosphorylation of mixed human muscles is not strongly associated with altered contractile performance.
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PMID:Myosin light chain phosphorylation and contractile performance of human skeletal muscle. 337 May 35


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