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At least 415 records · Page 23Linked to original sources
PubMed1990

Stretch-sensitive channels in developing muscle cells from a mouse cell line.

1. Recordings of single-channel activity were made from cell-attached patches on mouse C2 muscle cells at morphologically identifiable stages of myogenesis in vitro. We have identified Ca2(+)-permeable, cation-selective channels that are gated by applying suction to the patch electrode and by changes in membrane potential and have analysed single-channel properties as well as channel expression during myogenesis. 2. Single-channel activity could be detected when the membrane was held at steady negative potentials. With monovalent cations in the electrode, the single-channel current-voltage (i-V) relations were linear. The channel is permeable to Li+, Na+, K+, Rb+ and Cs+, but is not strongly selective among the monovalent cations as judged by measurements of single-channel conductance and reversal potential. 3. With 110 mM of either CaCl2 or BaCl2 as the only inward change carrier, slope conductances were approximately 13 and 24 pS and currents reversed at approximately +22 and +17 mV, respectively. The relative permeability of Ca2+ to K+ calculated from the constant-field equation was PCa/PK = approximately 2. 4. Channel openings occurred as bursts of brief openings and closings separated by much longer closed periods. Closed-time histograms were best fitted with three exponential components, while histograms of burst duration were best fitted with two exponential components, reflecting the short and long bursts in the single-channel records. 5. Applying suction to the patch electrode while recording at steady negative membrane potentials produced channel openings to discrete current levels. Mean channel open probability depended linearly on the square of the applied pressure and was greater at positive membrane potentials. The permeability of the channel to monovalent and divalent cations was indistinguishable from the spontaneous activity recorded at steady negative potentials. 6. Channel activity recorded from cell-attached patches in the absence of applied pressure depended on membrane potential increasing approximately e-fold per 38 mV with depolarization. Analysis of the kinetics of the response to membrane potential showed that the depolarization reduced the duration of the slowest component of the closed-time distribution. 7. The lanthanide cation gadolinium (Gd) reduced the amplitude of the unitary currents in a concentration-dependent manner. The amplitudes of both inward and outward currents were reduced to the same extent suggesting block is voltage-independent. Gd produced half-maximal inhibition of the unitary current at approximately 6 microM.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

Blood vessel ontogeny in upper extremity of man as related to developing muscles.

Vascular bed and its relationship to differentiating muscular tissue was studied in a set of 104 upper limbs of human embryos and foetuses, gradually increasing from 10 to 120 mm C-R length. Knowledge obtained on the ontogeny of vascular bed was supplemented by findings in 75 limbs of adults treated by preparation technique. Embryonic and foetal material was treated histochemically a--to demonstrate vascular bed reaction for alkaline phosphatase (AP), ATPase, and dipeptidylpeptidase IV (DPP IV), b--to study differentiating muscular tissue for enzyme--ATPase and tetrazoliumreductase (NaDH2, c--to distinguish muscular tissue elements with toluidine blue staining for degree of maturity. Observations concerned several items, namely a--the ontogeny of main arterial trunks in the forearm and hand, b--muscle fibre type differentiation in antebrachial muscular primordia, c--formation of vascular bed as related to differentiating muscular tissue in the forearm and hand. Therefore our results are grouped as follows: ad a--Arterial trunks differentiate along with other limb structures in 12-18 mm C-R length embryos. Thus in embryos above 18 mm C-R length antebrachial and hand trunks are fully formed. Vascular trunks differentiate from deep vascular network via gradual reduction and magistralization in conformity with the general laws of haemodynamics. All arterial trunks forming in the limb during the ontogeny branch off the original axial artery in regio cubiti. In a. radialis trunk it has been ascertained that this blood vessel does not originate from a. brachialis superficialis, as generally reported, but its formation conforms to the same general principles as blood vessel trunks. So it branches off the original axial artery, as other trunks do. A. mediana formed during vascular trunks differentiation later in the ontogeny does not obliterate but changes into the constant a. comitans n. mediani. ad b--First involved in differentiation in antebrachial muscular primordia are the "fast" type fibres (according to Peter et al., 1972) (fast glycolytic-FG-type fibres followed by fast oxidative glycolytic-FOG-type fibres) in 27-30 mm C-R length embryos. "Slow" type fibres (slow oxidative-SO-type fibres) may not be demonstrated histochemically in antebrachial muscles earlier than 45 mm C-R length foetuses. The maturity of muscular elements may be demonstrated by staining with toluidine blue on cytoplasm basophilia of cells. Sarcolytic myotubes in muscular primordia histochemically display typical features which distinguish them markedly from other differentiating muscle fibres.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenosine Triphosphatases↗
PubMed1999

Fetal myoblast clones contribute to both fast and slow fibres in developing rat muscle.

Retroviral cell lineage marking was used to investigate the role of cell lineage in fetal and neonatal rat muscle development. Clusters of infected cells, presumably myoblast clones, contribute cells to both slow primary and fast secondary fibres. Moreover, single clusters of marked cells contain both slow and fast primary fibres, suggesting that, at least during fetal life, single clones contribute nuclei to both fibres that are committed to remain slow and those that convert to a fast phenotype. The majority of fibres in individual fascicles of fetal muscle could be infected by a self-inactivating retroviral vector. Retroviral gene expression was markedly lower in non-muscle tissues, suggesting that fetal retroviral infection might target exogenous genes to mammalian muscle fibres during later life.

Age Factors↗
PubMed1993

Regulation and activity-dependence of N-cadherin, NCAM isoforms, and polysialic acid on chick myotubes during development.

Muscle development in vivo involves a complex sequence of cell-cell interactions in which secondary myotubes first form in association with primary myotubes and subsequently separate from them. We show here that during this process N-cadherin and the different structural forms of NCAM are regulated in a pattern that involves both temporal changes in expression and localization to particular regions of the muscle cell surface. In particular, levels of N-cadherin on maturing myotubes are decreased, and the form of NCAM synthesized by the muscle changes from a transmembrane non-polysialylated to a lipid-linked polysialylated membrane protein. Moreover, while NCAM was distributed on all myotube surfaces, the polysialyated form of NCAM was restricted to regions of the myotube surface that had recently separated from neighboring cells. We previously found that blockade of nerve-induced activity by d-Tubocurarine perturbed muscle cell interactions, resulting in a failure of myotubes to separate. We now show that this activity blockade also alters adhesion molecule expression. First, N-cadherin was no longer down-regulated in maturing myotubes, and its persistence on the surfaces of mature myotubes may partly explain their failure to separate. Secondly, the developmental switch from transmembrane to lipid-linked NCAM did not occur, and polysialylated NCAM was no longer formed. As the unusual physical properties of PSA have been proposed to impede cell-cell interactions, this alteration would also be expected to compromise cell separation. Together, these results suggest that the regulated expression of both N-cadherin and NCAM isoforms including their polysialylation, is an essential mechanism for the normal separation of secondary myotubes from primary myotubes.

Animals↗
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↗
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↗
PubMed1997

Accumulation and proliferation of adult leg muscle precursors in Manduca are dependent on innervation.

During metamorphosis, the larval thoracic legs of the moth Manduca sexta are replaced by new adult legs. The leg motoneurons do not die after the loss of the larval muscles, but persist to innervate the new adult leg muscles (Kent and Levine, 1988). The adult muscles form from myoblasts that originate in specific production sites within the legs and migrate to the sites of muscle formation, where they accumulate, proliferate, and fuse to form myofibers (Consoulas et al., 1996b). Throughout adult leg muscle development, there is a close association between nerves and the developing muscles, suggesting a role for the nervous system in myogenesis (Consoulas et al., 1996a). This prediction was confirmed and the role of the nervous system clarified in the present study by cutting the larval leg nerves prior to metamorphosis. Although myoblasts were generated and migrated normally in the operated leg, they failed to accumulate in the appropriate regions. The myoblasts did not die, but failed to proliferate and remained in the denervated legs as dispersed cells or as aggregates in inappropriate regions. In about 26% of cases, this resulted in the formation of adult legs that lacked muscles. In the remaining cases, however, delayed regeneration of the leg nerve occurred and small muscles appeared in the more proximal segments of the denervated legs. Each muscle fiber in these operated legs bore motor terminals belonging to axons of the leg nerves which had grown out from the proximal nerve stump and invaded the leg. Following the delayed appearance of motor axons, myoblasts aggregated and underwent proliferation and differentiation into muscle fibers. In a second set of experiments, denervation was performed later, after myoblasts had aggregated to establish anlagen. Myoblast proliferation was reduced but differentiation continued. These observations suggest that motor nerves are essential for both the accumulation of myoblasts into the correct areas of muscle development and the appropriate level of proliferation.

Aging↗
PubMed1980

The effects of partial denervation at birth on the development of muscle fibres and motor units in rat lumbrical muscle.

1. Two aspects of nerve-muscle development were studied in neonatal rats, the role of competition between motor neurones during the elimination of polyneuronal innervation, and the dependence of muscle fibre production upon the number of motor neurones innervating the muscle. 2. Rat lumbrical muscles were partially denervated at birth by cutting the lateral plantar nerve. Many muscles remained innervated by a single motor axon from the sural nerve. These motor units developed in the complete absence of competition from other motor units. In the adult muscles the number of innervated muscle fibres was approximately the same as at birth (about 120 muscle fibres). 3. In muscles that were totally denervated at birth, the normal post-natal production of muscle fibres was arrested. In partially denervated muscles, the production of new muscle fibres depended on the number of remaining motor units. The relationship between the total number of muscle fibres and the number of remaining motor units was fitted by a simple model. 4. The results suggest that in the lumbrical muscle, the decrease in motor unit size that occurs during normal development can be accounted for entirely by competition between motor nerve terminals. 5. The results also suggest that the normal post-natal increase in the total number of muscle fibres depends on a trophic interaction between the muscle and its innervation.

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↗
PubMed1996

Innervation regulates myosin heavy chain isoform expression in developing skeletal muscle fibers.

The influence of innervation on primary and secondary myogenesis and its relation to fiber type diversity were investigated in two specific wing muscles of quail embryo, the posterior (PLD) and anterior latissimus dorsi (ALD). In the adult, these muscles are composed almost exclusively of pure populations of fast and slow fibers, respectively. When slow ALD and fast PLD muscles developed in ovo in an aneurogenic environment induced after neural tube ablation, the cardiac ventricular myosin heavy chain (MHC) isoform was not expressed. The adult slow MHC isoform, SM2, appeared by embryonic day 7 (ED 7) in normal innervated slow ALD but was not expressed in denervated muscle. Analysis of in vitro differentiation of myoblasts from fast PLD and slow ALD muscles isolated from ED 7 control and neuralectomized quail embryos showed no fundamental differences in the pattern of MHC isoform expression. Newly differentiated fibers accumulated cardiac ventricular, embryonic fast, slow SM1 and SM3 MHC isoforms. Nevertheless, the expression of slow SM2 isoform in myotubes formed from slow ALD myoblasts only occurred when myoblasts were cultured in the presence of embryonic spinal cord. Our studies demonstrate that the neural tube influences primary as well as secondary myotube differentiation in avian forelimb and facilitates the expression of different MHC, particularly slow SM2 MHC gene expression in slow myoblasts.

Acetylcholinesterase↗
PubMed1981

The in situ staining of muscles during development with the cholinesterase technique.

Developing muscles from forelegs of 11- to 18-day-old mouse embryos were stained in situ for cholinesterase with the copper-ferrocyanide technique. The skin of the legs represents a diffusion barrier for the incubation medium. Therefore, in older embryos the skin was mechanically removed after trypsin digestion. In younger embryos the skin remained on the forelegs after trypsin treatment. With this technique it is possible to follow the establishment of the muscular pattern in the legs.

Animals↗
PubMed1994

Regulation of the rat muscle glycogen phosphorylase-encoding gene during muscle cell development.

The muscle isozyme of glycogen phosphorylase (MGP) catalyzes the hydrolysis hydrolysis of intracellular glycogen in mammalian tissues and is produced in skeletal muscle, brain and heart. The MGP gene is developmentally and neutrally regulated in skeletal muscle, but little is known about the gene's transcriptional regulation. We have isolated and characterized the 5' flanking region of rat MGP. Truncated portions of the MGP 5' flanking region were coupled to the bacterial cat reporter gene and used in transient transfection assays in the mouse muscle C2C12 cell line. The region between -211 and +62 contained the smallest regulatory domain capable of demonstrating developmentally regulated myogenic expression in C2C12 cells. This was in contrast with findings from another investigation that transfected this cell line with human MGP [Lockyer and McCracken, J. Biol. Chem. 266 (1991) 20262-20269]. A 172-nucleotide (nt) region between -839 and -666 functioned as a potent enhancer in C2C12 cells when coupled to its cognate promoter, but not when coupled to a simian virus 40 promoter. This rat MGP enhancer region is 78% identical to a comparable region of the human MGP 5' flanking region, but contains only one putative regulatory element that has been previously identified in other muscle genes. These data suggest that rat MGP transcription in C2C12 muscle cells is modulated by a potent enhancer that utilizes novel regulatory elements.

Amino Acid Sequence↗