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At least 19 recordsLinked to original sources
PubMed1990

Determinative mechanisms in secondary muscle lineages of ascidian embryos: development of muscle-specific features in isolated muscle progenitor cells.

Muscle cells of the ascidian larva originate from three different lines of progenitor cells, the B-line, A-line and b-line. Experiments with 8-cell embryos have indicated that isolated blastomeres of the B-line (primary) muscle lineage show autonomous development of a muscle-specific enzyme, whereas blastomeres of the A-line and b-line (secondary) muscle lineage rarely develop the enzyme in isolation. In order to study the mechanisms by which different lines of progenitors are determined to give rise to muscle, blastomeres were isolated from embryos of Halocynthia roretzi at the later cleavage stages when conspicuous restriction of the developmental fate of blastomeres had already occurred. Partial embryos derived from B-line muscle-lineage cells of the 64-cell embryo (B7.4, B7.5 and B7.8) showed autonomous expression of specific features of muscle cells (acetylcholinesterase, filamentous actin and muscle-specific antigen). In contrast, b-line muscle-lineage cells, even those isolated from the 110-cell embryo (b8.17 and b8.19), did not express any muscle-specific features, even though their developmental fate was mainly restricted to generation of muscle. Isolated A-line cells from the 64-cell embryos (A7.8) did not show any features of muscle differentiation, whereas some isolated A-line cells from the 110-cell embryos (A8.16) developed all three above-mentioned features of muscle cells. This transition was shown to occur during the eighth cell cycle. These results suggest that the mechanism involved in the process of determination of the secondary-lineage muscle cells differs from that of the primary-lineage muscle cells. Interaction with cells of other lineages may be required for the determination of secondary precursors to muscle cells. The presumptive b-line and A-line muscle cells that failed to express muscle-specific features in isolation did not develop into epidermal cells. Thus, although interactions between cells may be required for muscle determination in secondary lineages, the process may represent a permissive type of induction and may differ from the processes of induction of mesoderm in amphibian embryos.

Acetylcholinesterase↗
PubMed1979

The complete amino acid sequence of actins from bovine aorta, bovine heart, bovine fast skeletal muscle, and rabbit slow skeletal muscle. A protein-chemical analysis of muscle actin differentiation.

Complete amino acid sequences for four mammalian muscle actins are reported: bovine skeletal muscle actin, bovine cardiac actin, the major component of bovine aorta actin, and rabbit slow skeletal muscle actin. The number of different actins in a higher mammal for which full amino acid sequences are now available is therefore increased from two to five. Screening of different smooth muscle tissues revealed in addition to the aorta type actin a second smooth muscle actin, which appears very similar if not identical to chicken gizzard actin. Since the sequence of chicken gizzard actin is known, six different actins are presently characterized in a higher mammal. The two smooth muscle actins--bovine aorta actin and chicken gizzard actin--differ by only three amino acid substitutions, all located in the amino-terminal end. In the rest of their sequences both smooth muscle actins share the same four amino acid substitutions, which distinguish them from skeletal muscle actin. Cardiac muscle actin differs from skeletal muscle actin by only four amino acid exchanges. No amino acid substitutions were found when actins from rabbit fast and slow skeletal muscle were compared. In addition we summarize the amino acid substitution patterns of the six different mammalian actins and discuss their tissue specificity. The results show a very close relationship between the four muscle actins in comparison to the nonmuscle actins. The amino substitution patterns indicate that skeletal muscle actin is the highest differentiated actin form, whereas smooth muscle actins show a noticeably cloer relation to nonmuscle actins. By these criteria cardiac muscle actin lies between skeletal muscle actin and smooth muscle actins.

Actins↗
PubMed1989

Measurements of muscle stiffness, the electromyogram and activity in single muscle spindles of human flexor muscles following conditioning by passive stretch or contraction.

In experiments on adult human subjects we examined the effect on passive mechanical properties of a muscle by conditioning it with either an isometric contraction or passive muscle extension. The test measurement was the amount of muscle displacement (stiffness) and the accompanying EMG in response to a brief torque pulse. Two muscles were tested, flexor digitorum profundus (FDP) and brachialis. In FDP the discharge of single muscle spindles was recorded as well. After muscle extension and return to the initial length, passive stiffness was less than after an isometric contraction. The changes in stiffness were accompanied by changes in pattern of EMG and in the responses of muscle spindles. It is suggested that in resting muscle there are stable cross bridges between actin and myosin filaments of muscle fibres which largely determine the passive stiffness. Muscle extension leads to detachment of these cross bridges which then re-form at the longer length. Return of the muscle to its starting length leads to development of slack in muscle fibres because, stiffened by the presence of the stable cross bridges, they are unable to shorten. Slack in muscle fibres lowers their measured stiffness. Muscle contraction, on the other hand, will result in any preexisting slack being taken up by the actively shortening muscle fibres, thereby raising muscle stiffness. Stiffness in intrafusal fibres is likely to follow a similar pattern to that in extrafusal fibres, leading to changes in stretch responsiveness of muscle spindles and consequently in the reflex EMG. It is concluded that the changes in stiffness and accompanying reflexes observed in this study are likely to be seen, at least under some conditions, in normal movements.

Adult↗
PubMed1978

[Contractile properties of the striated muscle fibres of esophageal muscle in comparison with skeletal muscle in rats].

The contractile properties of the striated oesophageal muscle of the rat were studied in vitro at 35 degrees C and 25 degrees C. They were compared with those of the slow-twitch soleus muscle and the fast-twitch extensor digitorum longus (EDL) muscle of the same animals. The contraction time of the oesophageal muscle is 30 msec (+/- 2.5 msec S.E.) at 35 degrees C. It is little but significantly longer than those of the soleus muscle. It is remarkable that the twitch-tetanus ratio of the oesophageal muscle fibres is approximately twice that of the skeletal muscles. Immediately after a tetanic stimulation the amplitude of a single twitch of the fast EDL is increased (posttetanic potentiation); in the slow soleus muscle it is unchanged or decreased, however. Also the muscle fibres of the oesophagus exhibit a post-tetanic-potentiation, but this is smaller than in EDL. A decrease of the temperature of the bathing solution causes in preparations of the fast EDL a higher tension developed by a single twitch (cold potentiation). This is not detectable in preparations of the slow soleus muscle. The oesophageal muscle shows also a remarkable cold potentiation, but it is smaller than in EDL. An increase of the extracellular K+-concentration evokes a short-lasting contracture in the investigated rat muscles. The mechanical thresholds of the oesophageal muscle fibres are clearly higher than those of the soleus muscle but lower than those of the EDL. The striated oesophageal muscle fibres of the rat in spite of their low speed of contraction show some properties of muscle fibres of the fast twitch type.

Animals↗
PubMed1989

Roles of muscle activity and load on the relationship between muscle spindle length and whole muscle length in the freely walking cat.

The objective of this research was to compare the length of muscle spindles to the length of the whole muscle, during normal movements. Pairs of piezoelectric crystals were implanted near the origin and insertion of muscle fibres in the medial gastrocnemius (MG) muscle of cats. The distance between crystals was measured with pulsed ultrasound, the origin-to-insertion length of the MG muscle was measured with a transducer made of saline-filled silicone tubing, MG force was measured with a tendon force transducer and EMG activity was selectively recorded in the vicinity of implanted crystals. These signals were simultaneously recorded during posture or locomotion on a motorized treadmill. Three periods were identified in the step cycle, during which the relation between muscle length and spindle length changed dramatically. In period I (roughly corresponding to the late F and E1 phases of swing), the MG muscle and spindles followed similar length changes: both were stretched and then shortened by about 6 mm. In period II (corresponding to the stance phase, E2-E3) the MG muscle yielded under the weight of the body and was stretched by 1-3 mm, whereas the MG spindles typically continued shortening. In period III, the MG muscle shortened rapidly by 6-8 mm after the foot left the ground and then stretched again by about the same amount, whereas the spindles could remain nearly isometric. We attribute these large discrepancies in muscle and spindle length to the architecture of the MG muscle and the compliance of long tendinous elements in series with the spindles. We conclude that the length changes imposed on muscle spindles during voluntary movements are not simply related to the parent muscle length changes and cannot be estimated without taking into account the muscle architecture, the location of the spindle within the muscle, the level of muscle activation and the external load.

Animals↗
PubMed1990

Protein synthesis in skeletal muscle during starvation and refeeding: comparison of data from intact muscle and muscle biopsy material.

The intact extensor digitorum longus (EDL) preparation in rat is a well-documented model for assessing protein synthesis in skeletal muscle. Human muscle biopsy material has also been used, but the extent to which biopsy material is representative for evaluation of muscle protein synthesis has not been established. Therefore, the aim of this study was to compare protein synthesis in intact muscle and in muscle biopsy material simultaneously in rats. The animals (70 g) were divided into three groups: fed (n = 22), starved for 36 hours (n = 22), and refed for 24 hours (n = 19). Protein synthesis and RNA content were measured in each group. Protein synthesis was determined as the incorporation of 14-C-phenylalanine into muscle protein in the intact EDL muscle from one leg and in a muscle biopsy from the contralateral EDL muscle. The incorporation of 14-C-phenylalanine was linear over time in both preparations, but was consistently lower in the muscle biopsy compared with the intact muscle. The relative change in incorporation, in % of that obtained in the fed state, showed a decrease in incorporation after 36 hours of starvation, in both intact muscle and in muscle biopsy material, 33% +/- 10% and 42% +/- 6%, respectively. After 24 hours of refeeding, an overshoot in protein synthesis was seen, to 136% +/- 6% in the intact muscle and to 133% +/- 6% in the muscle biopsy, as compared with the fed state. The RNA content decreased during the starvation period from 21.6 +/- 0.7 to 14.5 +/- 0.4 mg RNA/g protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Projectin is an invertebrate connectin (titin): isolation from crayfish claw muscle and localization in crayfish claw muscle and insect flight muscle.

A filamentous protein was isolated from crayfish claw muscle. This protein had physiochemical properties very similar to vertebrate skeletal muscle connectin (titin), although its apparent molecular mass (approximately 1200 kDa) was considerably lower than that of connectin (approximately 3000 kDa). Polyclonal as well as monoclonal antibodies against chicken skeletal muscle connectin reacted with the 1200 kDa protein from crayfish claw muscle. Conversely, polyclonal antibodies against crayfish 1200 kDa protein cross-reacted with chicken connectin. Circular dichroic spectra indicated the abundance of beta-sheet structure (approximately 60%). Low-angle shadowed images showed filamentous structures (0.2-0.5 microns) by electron microscopy. Proteolysis of the 1200 kDa protein by alpha-chymotrypsin or V8 protease rapidly resulted in formation of 1000 kDa or 1100 and 800 kDa peptides. The amino acid composition was very similar to those of vertebrate connectins and of honeybee flight muscle projectin. Based on the molecular weight and amino acid composition, the 1200 kDa protein is regarded to be crayfish projectin. Immunofluorescence and immunoelectron microscopy revealed that crayfish projectin was localized in the A/I junction area and A-band except for its centre region in crayfish claw muscles. Polyclonal antibodies against crayfish claw muscle projectin reacted with 1200 kDa projectin of honeybee and beetle flight muscle. A monoclonal antibody against chicken skeletal muscle connectin also reacted with honeybee and beetle projectin. Immunoelectron microscopic observations revealed that anti-crayfish projectin antibodies bound the connecting filaments linking the Z-line and the thick filaments up to the M-line of honeybee muscle sarcomere. Anti-crayfish projectin antibodies bound the I-band region near the Z-line of beetle flight muscle. It is concluded that the 1200 kDa projectin from crayfish claw muscle is an invertebrate connectin (titin). Recent work with locust flight muscle mini-titin (Nave & Weber, 1990) is in good agreement with the present study, except that the isolated mini-titin estimated as 600 kDa appears to be a proteolytic product (approximately 1100 kDa) of the parent molecule (approximately 1200 kDa).

Actin Cytoskeleton↗
PubMed2025

Impact of Muscle Quality on Muscle Strength and Physical Performance Beyond Muscle Mass or Diabetes Status.

BACKGROUND: Muscle quality, represented by myosteatosis, is recognized as an important factor in sarcopenia. In this study, we aimed to determine the associations between myosteatosis, muscle strength and physical performance among the elderly South Korean population. METHODS: We included 1440 participants (mean age 62.7&#x2009;&#xb1;&#x2009;6.2&#x2009;years) from the Korean Genome and Epidemiology Study (KoGES). Based on the computed tomography attenuation of mid-thigh imaging, the total muscle area (TMA), normal-attenuation muscle area (NAMA), low-attenuation muscle area (LAMA) and inter-intramuscular adipose tissue (IMAT) and its indices were used to evaluate myosteatosis. Muscle strength was evaluated using hand grip strength, whereas physical performance was evaluated through 4-m gait speed, a 30-s sit-to-stand test and 2-min walking test. RESULTS: Of the 1440 patients, 51.5% were women, and 37.2% had diabetes. With aging, the LAMA index gradually increased, and the NAMA index gradually decreased in both men and women (p for trend <&#x2009;0.001). The NAMA index was positively associated, whereas the LAMA and IMAT indices were negatively associated with muscle strength and physical performance after adjusting for age and sex. Higher tertiles of the NAMA index were consistently associated with improved physical performance across all appendicular skeletal muscle tertiles. The relationship between the NAMA index or LAMA index and muscle strength and physical performance did not differ according to diabetic status. Regular exercise was associated with a higher NAMA index and a lower LAMA index in the non-diabetic group; however, no significant difference in muscle quality was observed in the diabetic group in relation to exercise. CONCLUSIONS: Reduced myosteatosis was positively associated with greater muscle strength and better physical performance in both men and women, regardless of muscle mass or diabetes status; improving myosteatosis may be a therapeutic target for the prevention of sarcopenia.

Humans↗
PubMedDate not supplied

Fine structure of muscle in human disuse atrophy: significance of proximal muscle involvement in muscle disorders.

The universal occurrence of weakness of skeletal musculature on disuse, however produced, and the paucity of published reports on the fine structural changes in human disuse atrophy, prompted the present investigation. The quadriceps muscle of a leg immobilized in plaster cast (for fracture) and of the opposite non-immobilized limb was biopsied in four adult males, after periods of immobilization from 50 to 75 days. These 8 muscle specimens were examined for histopathological changes, and muscle fibre diameters were measured by micrometry from paraffin sections. The histograms revealed a larger proportion of small fibres (less than 20 micron) and a smaller proportion of large fibres (greater than 40 micron) in the immobilized limb compared to the opposite. Thus, light microscopy showed only atrophic changes. This was confirmed by electronmicroscopy, where atrophy of few to several muscle fibres was seen in the form of loss of myofibrils, collapse and folding of the basement membrane and prominence of glycogen or muscle nuclei. The atrophic change was more severe in the immobilized limbs, but it was also noticeable in all the non-immobilized limbs. Degenerative changes, especially disorganization and breakdown of myofibrils, and fragmentation of plasma membrane, were also seen in occasional atrophied muscle fibres, again more frequently in the immobilized limb. Lipofuscin was often found accumulated in muscle fibres and occasionally in endothelial cells of intramuscular blood vessels; the latter showed prominent pinocytotic vesicles or thickened basement membrane. It is concluded that both atrophy and degeneration of fibres of proximal muscles can occur as non-specific consequences of disuse of the limb in man, that degeneration is a latter and more severe change, that muscles even of the non-immobilized leg are subjected to disuse atrophy during bed-rest, and that the proximal muscles in man seem to have a natural susceptibility to atrophy and degeneration in any muscular disorders.

Adult↗
PubMed2026

Skeletal Muscles Do Not Compete for Growth: Activating Additional Muscle Mass Does Not Compromise Changes in Muscle Size.

Kataoka, R, Yamada, Y, Hammert, WB, Sallberg, RW, Kang, A, Song, JS, Kassiano, W, Metcalf, EE, and Loenneke, JP. Skeletal muscles do not compete for growth: Activating additional muscle mass does not compromise changes in muscle size. J Strength Cond Res 40(9): 1043-1049, 2026-This study investigated whether the magnitude of muscle size and strength differed based on the amount of muscle recruited during training sessions. One hundred five untrained individuals were randomly assigned to 1 of 3 groups: low-load unilateral elbow flexion exercise (a) to failure (LL-Failure, n = 36), (b) to failure and low-load knee extension exercise to failure (LL-Failure + Legs, n = 33), or (c) a time-matched nonexercise control (CON, n = 36). Training groups completed 18 supervised sessions over 6 weeks (2 sets at 30% 1 repetition maximum [1RM] to failure). LL-Failure + Legs group performed 4 additional sets of knee extension exercise in each leg (20-30 RM). Muscle thickness on the anterior upper arm (60 and 70% sites) and elbow flexor 1RM strength of the trained arm were measured at pretesting and posttesting. Changes were compared using the ANCOVA function of Bayes Factors for Informative Hypotheses (prevalues as the covariate). Specific hypotheses were evaluated by comparing Bayes factors and the posterior probabilities between models. Six weeks of training led to increases in muscle size and strength. However, performing additional leg exercise did not attenuate the muscle growth in the anterior upper arm (0.19 cm) compared with performing only arm exercise to failure (0.18 cm). Changes in 1RM strength also did not differ between training groups (0.32 and 0.25 kg for LL-Failure and LL-Failure + Legs, respectively). Overall, there was no evidence for competition of adaptations in muscle size and strength under uncontrolled nutritional conditions. Whether greater training volume or limited nutrient intake induces a competition for resources warrants further investigation.

Humans↗
PubMedDate not supplied

Turnover rates of muscle proteins in cardiac, skeletal, and smooth muscle: turnover rate related to muscle function.

The turnover rate of muscle proteins was related to the physiological function of the muscle in dogs, fowl, rats, and mice. The turnover rates of mixed muscle proteins were most rapid in cardiac muscle, intermediate in red tonic and mixed fiber-type muscles, and slowest in white twitch skeletal muscle. This same progression in turnover rates also was shown in the subcellular fractions of muscle-sarcoplasmic and myofibrillar proteins-as well as in purified proteins, myosin, and tropomyosin. The RNA concentration of muscle was highly correlated with the protein turnover rate, and the RNA activity, i.e., the translational efficiency of the RNA, was similar in the different muscle types.

Animals↗
PubMed1989

Increased muscle tension and reduced elasticity of affected muscles in recent-onset Graves' disease caused primarily by active muscle contraction.

In 3 patients with Graves' disease of recent onset, length-tension diagrams were made during surgery for squint under eyedrop anesthesia. The affected muscles were found to be very stiff when the other eye looked straight ahead. It was expected that these stiff muscles would be able to shorten to some extent but would be unable to lengthen, due to fibrosis of the muscle. We found that the affected muscles did not shorten very much when the other eye looked into the field of action of the muscle. Unexpectedly however, they lengthened considerably when the other eye looked out of the field of action of the muscle. This finding implies that the raised muscle tension and reduced elasticity of affected muscles in these cases of Graves' disease of recent onset were primarily caused by active muscle contraction, not by fibrosis.

Diplopia↗
PubMed1992

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↗
PubMed1989

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↗
PubMed1972

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↗
PubMed1978

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↗