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PubMed1988

Functional significance of myosin transitions in single fibers of developing soleus muscle.

The maximal velocity of shortening and myosin heavy chain (MHC) composition of single, chemically skinned fibers from neonatal and adult rat soleus muscles were examined to determine the relationship between these parameters during slow muscle development in the rat. In addition, the MHC composition of bundles of fibers from soleus muscles at the same ages was studied. The MHC compositions were examined using sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. The results from the bundles of fibers indicate that from 3 days to 5 mo postnatal, the rat soleus contains predominantly MHCs that migrate in the vicinity of the MHC from adult slow muscle. From 14 days to 2 mo postnatal, there are also significant amounts of additional MHCs that comigrate on SDS gels with those characteristic of adult rat fast muscle. All the fibers studied at 3 and 7 days postnatal and at 5 mo and the majority of fibers from 14 days to 2 mo postnatal had relatively low shortening velocities. A few fibers from the latter group had significantly higher velocities. The faster fibers at each age had greater amounts of the MHCs that comigrate with the adult fast-type MHC on SDS gels. Thus the velocity of shortening of single fibers from the rat soleus muscle appears to be related to MHC composition during postnatal development.

Animals↗
PubMed1989

A cofilin-like protein is involved in the regulation of actin assembly in developing skeletal muscle.

An actin-binding protein of 20 kDa (called 20K protein) was purified from the sarcoplasmic fraction of embryonic chicken skeletal muscle. The properties of this protein were very similar to cofilin, which was discovered in porcine brain (Nishida et al. (1984) Biochemistry, 23, 5307-5313): it bound to both G- and F-actin, inhibited actin polymerization in a pH-dependent manner, inhibited binding of tropomyosin to F-actin, and had almost the same molecular size and pI as cofilin. A specific monoclonal antibody to 20K protein (MAB-22) was prepared to examine the expression and location of 20K protein during skeletal muscle development. When the whole protein lysates of embryonic and post-hatched chicken skeletal muscles were examined by means of immunoblotting combined with SDS-PAGE, 20K protein was detected in skeletal muscle through the developmental stages. Location of 20K protein in the cells differed between the embryonic and adult tissues; immunofluorescence staining of the cryosections of embryonic muscle with MAB-22 visualized irregular dot-like structures, but adult muscle sections were stained faintly and uniformly. 20K protein was present as a complex with actin in embryonic muscle, as judged by the ability to bind to a DNase I affinity column, while the same protein was free from actin in the cytoplasm of adult muscle. From these results, it is suggested that 20K protein regulates actin assembly transiently in developing skeletal muscle.

Actin Depolymerizing Factors↗
PubMed1989

Satellite cell and growth factor involvement in skeletal muscle growth.

The activity of the satellite cell, discovered by Alexander Mauro, is of fundamental importance in postnatal skeletal muscle development, muscle adaptation to certain activity stimuli, and to muscle fiber regeneration following injury and transplantation operations. There are numerous mitogens and growth factors that influence satellite cell proliferation and differentiation in vitro and likely in vivo. The best understood purified growth factors are fibroblast growth factor (FGF), the insulin-like growth factors (IGF-I and -II), and transforming growth factor-beta (TGF-beta). Soluble extracts from injured muscle and chronically stretched muscle are also known to be mitogenic and are yet to be purified. Skeletal muscle development, hypertrophy, and regeneration can be viewed as points on a continuum with respect to the regulatory mechanisms of myogenic cell growth. The occurrence of fiber hyperplasia differs amongst some models of activity-induced growth and may reflect differences in the magnitude of the stimulus relative to the capacity of fibers to adapt. The relationships between the mechanical and environmental events coincident with an activity or injury stimulus and the role of specific muscle fiber satellite cell populations and growth factors are fertile areas for investigation. Insights from these experiments will yield a comprehensive understanding of the muscle growth process at the molecular, cellular, and tissue levels, and have implications for development and aging, health, disease, and adaptation.

Adaptation, Physiological↗
PubMed1985

Gating kinetics of nonjunctional acetylcholine receptor channels in developing Xenopus muscle.

The development of nonjunctional acetylcholine (ACh) receptor gating kinetics was studied in myotomal muscle of Xenopus laevis by spectral analysis of ACh-induced noise. The results are consistent with the idea that there is a developmental shift in relative numbers of receptors with fast and slow gating kinetics. For about the first 20 hr following the onset of ACh sensitivity, the majority of channel openings contributing to the ACh noise were slow, having an apparent mean open time of about 3 msec. Shortly before the time of hatching, there began to appear a significant contribution to the noise from channels having a mean open time of less than 1 msec. The relative amount of fast channel activity increased during the 2 days following hatching, and by the age of maturity of the myotomal synapse, most of the ACh noise arose from fast channel activity. A comparison of nonjunctional kinetics with synaptic currents at maturity suggests that the control of channel gating time is similar at junctional and nonjunctional regions.

Animals↗
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↗
PubMed1988

The diagnosis of temporomandibular joint disease: two-compartment arthrography and MR.

The reliability and accuracy of two-compartment temporomandibular joint (TMJ) arthrography was compared with MR imaging on the basis of an analysis of surgical findings obtained from joints that had been studied preoperatively with arthrography or MR or, in some cases, both procedures. Seven hundred forty-three consecutive TMJ arthrograms were successfully obtained in a total of 443 patients by using a single 27-gauge needle and a two-compartment technique in each joint. There was a 100% correlation with surgical findings in 218 radiologically abnormal joints operated on within 90 days of arthrography with respect to the presence or degree of meniscus displacement and normal or abnormal disk morphology and function. In 604 patients 1052 TMJs were studied with high-field-strength surface-coil MR. Surgical findings were available for correlation in 170 of the joints studied. Forty-three joints were studied with both two-compartment arthrography and MR. Eight operated joints had been imaged successfully with both two-compartment arthrography and MR. Both methods of evaluation provided highly reliable and accurate information regarding meniscus position and shape. Arthrography was superior to MR in detecting capsular adhesions and the presence or absence of perforation of the disk or meniscus attachments. Simple meniscectomy (with or without insertion of a temporary Silastic TMJ implant) was the most frequently performed surgical procedure in the series, followed by meniscus repositioning procedures. Joint effusions, failed TMJ implants, and avascular necrosis were demonstrated best with MR. Soft-tissue lesions, including intrinsic degeneration of the meniscus, anomalous muscle development, muscle atrophy, tendinitis, and injuries such as contusions and hematomas, were demonstrated only with MR. Partial-flip-angle GRASS (gradient-recalled acquisition in the steady state) techniques permit both fast scanning and study of functional joint dynamic. Joint fluid may appear as high signal intensity on GRASS images because of T2*-weighting. We recommend MR as the procedure of choice for diagnosis of uncomplicated internal derangements of the TMJ. Two-compartment arthrography with videofluoroscopy is an important ancillary procedure that should be performed whenever capsular adhesions or perforations are suspected and not demonstrated with MR and whenever MR is inconclusive.

Arthrography↗
PubMed1989

The effect of load on the phenotype of the developing rat soleus muscle.

In newborn Wistar rats the load on the soleus muscle was reduced by removing the tibialis anterior (TA) and extensor digitorum longus (EDL) muscles. Eighteen days later the soleus muscles were removed from both the operated and control legs and examined physiologically and histologically. The time course of twitch contraction of the soleus on the operated side was not significantly different from that of control muscles, but the muscles developed less tension. The decreased tension was consistent with a smaller number of muscle fibres. Histochemical and immunocytochemical examination showed that in the operated muscle, fewer fibres reacted with an antibody against slow myosin, while the number of fibres that reacted for alkali-preincubated ATPase, indicative of neonatal or adult fast myosin, was increased. Some fibres expressed both types of myosin. These findings suggest that a reduced load delays the phenotypic expression of slow myosin isoform in the developing soleus muscle.

Animals↗
PubMed1990

Pharmacological block of chloride channels of developing rat skeletal muscle affects the differentiation of specific contractile properties.

A specific chloride channel blocker, anthracene 9-carboxylic acid was locally applied for 8-9 days on the extensor digitorum longus muscle of 7-8-day-old rats. The effects of chronic anthracene 9-carboxylic acid treatment on muscle development, were evaluated in vitro on the electrical properties with intracellular microelectrodes and in vivo on the contractile parameters by recording isometric concentrations. Our data show that the treatment prevented the normal development of chloride conductance so that by 15 days of age it was 45% lower in fibers of the treated muscles when compared to age-related control fibers. Potassium conductance was not significantly changed by the treatment. In vivo the anthracene-9-carboxylic acid-treated muscles were slower to contract and relax; having a 20% slower time to peak twitch force and time of half relaxation. These muscles were also 32% less fatiguable with respect to the controls. Moreover, in most of the treated muscles tetanic contractions during high-frequency stimulation were not maintained. The block of chloride channels in developing striated fibers appears to affect the differentiation of specific properties of fast skeletal muscle such as the speed of contraction.

Animals↗
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↗
PubMed1990

The expression of myosin genes in developing skeletal muscle in the mouse embryo.

Using in situ hybridization, we have investigated the temporal sequence of myosin gene expression in the developing skeletal muscle masses of mouse embryos. The probes used were isoform-specific, 35S-labeled antisense cRNAs to the known sarcomeric myosin heavy chain and myosin alkali light chain gene transcripts. Results showed that both cardiac and skeletal myosin heavy chain and myosin light chain mRNAs were first detected between 9 and 10 d post coitum (p.c.) in the myotomes of the most rostral somites. Myosin transcripts appeared in more caudal somites at later stages in a developmental gradient. The earliest myosin heavy chain transcripts detected code for the embryonic skeletal (MHCemb) and beta-cardiac (MHC beta) isoforms. Perinatal myosin heavy chain (MHCpn) transcripts begin to accumulate at 10.5 d p.c., which is much earlier than previously reported. At this stage, MHCemb is the major MHC transcript. By 12.5 d p.c., MHCpn and MHCemb mRNAs are present to an equal extent, and by 15.5 d p.c. the MHCpn transcript is the major MHC mRNA detected. Cardiac MHC beta transcripts are always present as a minor component. In contrast, the cardiac MLC1A mRNA is initially more abundant than that encoding the skeletal MLC1F isoform. By 12.5 d p.c. the two MLC mRNAs are present at similar levels, and by 15.5 d p.c., MLC1F is the predominant MLC transcript detected. Transcripts for the ventricular/slow (MLC1V) and another fast skeletal myosin light chain (MLC3F) are not detected in skeletal muscle before 15 d p.c., which marks the beginning of the fetal stage of muscle development. This is the first stage at which we can detect differences in expression of myosin genes between developing muscle fibers. We conclude that, during the development of the myotome and body wall muscles, different myosin genes follow independent patterns of activation and accumulation. The data presented are the first detailed study of myosin gene expression at these early stages of skeletal muscle development.

Animals↗
PubMed1989

Immunofluorescent localization of desmin and vimentin in developing cardiac muscle of Syrian hamster.

The distributions of desmin and vimentin were examined in frozen sections of cardiac muscle from embryonic, newborn, and adult Syrian hamster by using immunofluorescent methods. Frozen sections of newborn and adult skeletal muscle were used for comparison. Cardiac myocytes from day 9 in utero embryos already show a clear association of desmin with the sarcomeric myofibrils. In newborn hearts, desmin is localized in the myofibrillar Z-line areas as well as in the peripheral cytoplasm of the cell. Three days after birth, desmin is associated with the intercalated discs. Thus, in adult cardiac muscle, desmin is present in both Z-bands and intercalated discs. Skeletal muscle of newborn and adult hamster also contains desmin associated with the Z-lines of myofibrils. Vimentin is associated with the myofibrils of day 9 in utero cardiac muscle cells. The protein remains associated with the myofibrillar Z-lines in the newborns and adults. No detectable staining for vimentin was observed in newborn or adult hamster skeletal muscle. The existence of vimentin as well as desmin in differentiated cardiac muscle may be a consequence of the somewhat more epithelial-like nature of cardiac cells as compared to skeletal muscle syncitia.

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↗