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At least 73 records · Page 4Linked to original sources
PubMed1977

Effects of innervation on acetylcholine sensitivity of developing muscle in vitro.

1. Chick embryo skeletal muscle fibres were grown in culture. The acetylcholine (AACh) sensitivity of non-innervated fibres was compared with that of fibres innervated in vitro by chick embryo ciliary ganglion neurones. 2. The general pattern of ACh sensitivity was unchanged by innervation: ACh hot spots were superimposed on a background of uniform ACh sensitivity. 3. Quantitative comparisons revealed two differences between non-innervated and innervated fibres. First, hot spots were encountered about one third more often on innervated fibres. Secondly, about one-third of the hot spots on innervated fibres had significantly higher ACh sensitivities than the remainder, which were similar to those on control fibres. 4. Apossible explanation of these results is that nerves which form synapses induce the appearanceof end-plates which have higher ACh sensitivities than the pre-existing ACh hot spots.

Acetylcholine↗
PubMed1991

[The embryonic development of iridial muscles].

Development of iridial muscles was observed in 116 fetal eyes (72 human embryos 7 weeks to full gestation). Bundles of microfilaments with local high density spots appeared in the cytoplasm of the anterior pigment epithelium early in 10 week embryos. The high density spots later grew to be the dense-bodies in the myofilaments, the original structure of the pupillary sphincter. In embryos of 4 1/2 months, blood capillaries grew into the sphincter, which was fully developed in the 6th month, and myofilaments of the dilator muscles began to appear in the cytoplasm of peripheral anterior pigment epithelium, with villous protrusions toward the stroma. Many myofilaments with scattered dense-bodies were seen in the protrusions. It was thus confirmed that both the sphincter and dilator muscles originated from the iridial anterior pigment epithelium of neuro-ectoderm; however, the former developed fully to form independent smooth muscle bundles, while the latter was less developed and remained part of the pigment epithelium (myo-epithelium). The appearance of both muscles was earlier than previously reported.

Actin Cytoskeleton↗
PubMed1979

Synthesis of the calcium transport ATPase of sarcoplasmic reticulum and other muscle proteins during development of muscles cells in vivo and in vitro.

The effect of medium Ca2+ concentration upon the concentration and the rate of synthesis of muscle proteins was investigated in chicken pectoralis muscle cultures. There is an easily identifiable class of muscle protein which includes the Ca2+-ATPase of sarcoplasmic reticulum, myosin, troponin C, ATP : creatine phosphotransferase, muscle specific actin, tropomysin 1 and 2, and muscle hemagglutinin, which show a large increase in concentration during normal development. The increased synthesis of these proteins was inhibited, without inhibition of cell proliferation, in culture media of relatively low Ca2+ concentration, 0.05--0.3 mM, where fusion was prevented. Similar medium Ca2+ concentration was required for the expression of all these proteins, suggesting their coordinate regulation. The proteins are denoted as 'calcium-modulated proteins'. The increased Ca2+ transport activity of sarcoplasmic reticulum in cultured chicken pectoralis muscle cells during development at 1.8 mM medium calcium concentration represents de novo synthesis of the Ca2+ transport ATPase, as shown by immunoprecipitation, active site labeling and direct identification of the Ca2+ transport ATPase on two-dimensional gel electropherograms of whole muscle homogenates. The concentration and the turnover rate of the majority of the muscle proteins is not affected significantly by medium Ca2+ concentration between 0.06 and 1.8 mM. It is proposed that increase in cytoplasmic free Ca2+ concentration during fusion plays a central role in the regulation of the synthesis of calcium-modulated proteins.

Acetylcholinesterase↗
PubMed1976

Sensory terminals on extrafusal muscle fibres in myotendinous regions of developing rat muscles.

Axon terminals were observed to form neuromuscular contacts with extrafusal muscle fibres in myotendinous regions of developing rat muscles up to 5 days after birth. These neuromuscular contacts are found in fascicles of muscle fibres connected with differentiating Golgi tendon organs. Axon terminals establishing these contacts are obviously sensory, since they do not degenerate after de-efferentation performed in neonatal rats. The terminals contain mainly clear and dense core vesicles and form neuromuscular connections resembling developing motor endplates, with a cleft about 60 nm wide and basal lamina interposed between the axolemma and the sarcolemma. Each terminal, however, also forms a close contact in a restricted region where the basal lamina is missing; there the cleft is reduced to 20 nm and the axolemmal and sarcolemmal membranes are linked by desmosome-like attachment plaques. After the fifth postnatal day, axon terminals become detached from muscle fibres and are only found among collagen bundles of the tendon organ. The functional significance of these temporary neuromuscular contacts is not clear.

Animals↗
PubMed1977

Transitional stages in the histochemical development of muscle fibres during post-natal growth.

Serial frozen sections of longissimus dorsi muscles from seven pigs at different live weights (13 to 127 kg) were reacted for ATPase by the calcium method at an alkaline pH and for NADH oxidative activity. One hundred muscle fibres from each animal were identified individually in serial sections and their staining intensity was measured with a microscope photometer at 600 nm. For each section, staining intensity of fibres (% tranmission) was measured and converted to the nearest one-tenth unit of the range from the darkest to the lightest staining fibres. Frequency of occurrence of fibre types was plotted on a 10 X 10 grid using the range co-ordinates for NADH oxidative activity (vertical) and ATPase activity (horizontal). The commonly recognized histochemical fibre types in this muscle appeared as crowded areas in the grid but, in many cases, these areas were part of a continuous 'L' shaped range, a continuous but skewed distribution with regard to NADH oxidative activity was detected. In fibres with NADH oxidative activity of 0.6 to 1.0 units of the range, a continuous but irregular distribution with regard to ATPase activity was detected. Within this range, there was some evidence of a growth-related shift towards weaker ATPase activity.

Adenosine Triphosphatases↗
PubMed1992

Assembly of contractile and cytoskeletal elements in developing smooth muscle cells.

Specific developmental changes in smooth muscle were studied in gizzards obtained from 6-, 8-, 10-, 12-, 14-, 16-, 18-, and 20-day chick embryos and from 1- and 7-day posthatch chicks. Myoblasts were actively replicating in tissue from 6-day embryos. Cytoplasmic dense bodies (CDBs) first appeared at Embryonic Day 8 (E8) and were recognized as patches of increased electron density that consisted of actin filaments (AFs), intermediate filaments (IFs), and cross-connecting filaments (CCFs). Although the assembly of CDBs was not synchronized within a cell, the number, size, and electron density of CDBs increased as age increased. Membrane-associated dense bodies (MADBs) also could be recognized at E8. The number and size of MADBs increased as age increased, especially after E16. Filaments with the diameter of thick filaments first appeared at E12. Smooth muscle cells were able to divide as late as E20. The axial intermediate filament bundle (IFB) could first be identified in 1-day posthatch cells and became larger and more prominent in 7-day posthatch cells. Immunogold labeling of 1- and 7-day posthatch cells with anti-desmin showed that the IFB contained desmin IFs. The developmental events during this 23-day period were classified into seven stages, based primarily on the appearance and the growth of contractile and cytoskeletal elements. These stages are myoblast proliferation, dense body appearance, thick filament appearance, dense body growth, muscle cell replication, IFB appearance, and appearance of adult type cells. Smooth muscle cells in each stage express similar developmental characteristics. The mechanism of assembly of myofilaments and cytoskeletal elements in smooth muscle in vivo indicates that myofilaments (AFs and thick filaments) and filament attachment sites (CDBs and MADBs) are assembled before the axial IFB, a major cytoskeletal element.

Animals↗
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↗
PubMed1990

Development of muscle nerve in the teleost fish, medaka.

The entire process of normal development of a muscle nerve to a muscle (middle interradial muscle) in the tail region of the medaka (Oryzias latipes) is briefly reported. The nerve was stained immunohistochemically by using anti-neurofilament protein antibodies or stained by HRP and DiI labeling methods. The muscle was stained immunohistochemically by using anti-troponin T and anti-desmin antibodies. The smallness and transparency of the medaka embryos provide us with an opportunity to examine nerve-muscle development in whole-mount specimens. Our observations suggest that prior to the appearance of the middle interradial muscle a neural pathway has established, extending from the starting point to the 'door step' of the muscle.

Animals↗
PubMed1992

Muscle fiber pattern is independent of cell lineage in postnatal rodent development.

Muscle fibers specialized for fast or slow contraction are arrayed in characteristic patterns within developing limbs. Clones of myoblasts analyzed in vitro express fast and slow myosin isoforms typical of the muscle from which they derive. As a result, it has been suggested that distinct myoblast lineages generate and maintain muscle fiber pattern. We tested this hypothesis in vivo by using a retrovirus to label myoblasts genetically so that the fate of individual clones could be monitored. Both myoblast clones labeled in muscle in situ and clones labeled in tissue culture and then injected into various muscles contribute progeny to all fiber types encountered. Thus, extrinsic signals override the intrinsic commitment of myoblast nuclei to particular programs of gene expression. We conclude that in postnatal development, pattern is not dictated by myoblast lineage.

Animals↗
PubMed1992

Association of titin and myosin heavy chain in developing skeletal muscle.

To understand molecular interactions that organize developing myofibrils, we examined the biosynthesis and interaction of titin and myosin heavy chain in cultures of developing muscle. Use of pulse-labeling, immunoprecipitation, and a reversible cross-linking procedure demonstrates that within minutes of synthesis, titin and myosin heavy chain can be chemically cross-linked into very large, detergent-resistant complexes retaining many features of intact myotubes. These complexes, predominantly of titin and myosin, occur very early in myofibrillogenesis as well as later. These data suggest that synthesis and assembly of titin and myosin are temporally and spatially coordinated in nascent myofibrils and support the hypothesis that titin molecules help to organize sarcomere formation.

Animals↗
PubMed1975

Sodium and calcium components of the action potential in a developing skeletal muscle cell line.

1. Developmental changes in action potential properties were studied in a clonal rat skeletal muscle cell line. 2. Small action potentials were evoked in mononucleate myoblasts. No spike was seen in Na-free saline. A similar spike was evoked in a medium where all NaCl was replaced by LiCl. No spike was evoked when NaCl was replaced by CsCl. 3. Action potentials overshot zero membrane potential in multinucleate myotubes. The action potential was composed of two components, an initial fast spike and a hump on the falling phase or in some cases a distinct second peak. 4. Teh overshoot of the initial fast spike decreased when the external Na concentration was decreased. 5. In saline with 10 mM-Ca the second component often formed a distinct peak following the initial fast spike. A slow regenerative potential was evoked in Na-free media with a depolarizing current pulse. 6. In saline containing BaCl-2 instead of CaCl-2 there was always a second peak, the overshoot of which changed with external Ba concentration. A slow regenerative potential was evoked in Na-free, Ba-saline. The membrane conductance at the peak of the Ba-action potential was larger than in the resting state. 7. In adult rat skeletal muscle, the shape of the action potential was not changed when Ca was replaced by Ba. No action potential was evoked in Na-free Ba-saline or Ba-saline with tetrodotoxin (3 times 10-7 M). 8. The significance of the Ca component in the developing muscle is discussed.

Action Potentials↗
PubMed1976

Postnatal cytochemical development of muscle fibers in segmental tail muscles of the rat.

Postnatal development of extrafusal and intrafusal muscle fibers was examined histochemically in segmental tail muscles of the rat. At birth all fibers show a strong reaction for myosin ATPase, uniformity in diameter, and homogeneity in staining intensity. During the first postnatal week, the muscle fibers undergo gradual hypertrophy and hyperplasia but they all maintain the same intense homogeneous staining pattern for the enzyme. By day 9, further differentiation of the muscle fibers results in the formation of a second intrafusal fiber type while the extrafusal fibers are still relatively homogeneous. Finally, two kinds of extrafusal fiber and a third type of intrafusal fiber can be distinguished by day 21. This histochemical fiber pattern is essentially maintained in the adult. These findings show that fiber type development in rat tail muscles lags behind the usual time course of myogenesis known to occur in more rostral regions of the animal. It also indicates that histochemical differentiation of intrafusal fibers in these muscles does not parallel that which occurs in extrafusal fibers. It is likely that arrival and initial contact of sensory nerve terminals on developing intrafusal fibers at day 7 directly influences their relatively early histochemical heterogeneity.

Adenosine Triphosphatases↗