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PubMed1982

Phosphorylation of tropomyosin during development in mammalian striated muscle.

Alpha-Tropomyosin from rat cardiac muscle was shown by two-dimensional gel electrophoresis to become phosphorylated when tissue slices were incubated in Eagle's medium supplemented with 32Pi. In the adult rat and mouse heart the level of phosphorylation was approximately 30% but the level was much higher in the foetal heart (60-70%). A similar developmental trend was observed in skeletal muscle from the rat and mouse, where phosphorylated forms of both alpha- and beta-tropomyosins were observed. When rat cardiac cells were grown in tissue culture in the presence of 32Pi, radioactivity was incorporated into the region of the gel containing tropomyosin.

Animals↗
PubMed1978

Some quantitative biochemical evaluations of developing skeletal muscles in the human foetus.

This study was performed to obtain a more precise quantitative estimation of oxidative and glycolytic potentials and stores of various substrates of the muscles in the human foetus. The material consisted of muscle samples from different muscles, a total of 166 muscle specimens from 65 foetuses and 55 skeletal muscle specimens from 53 infants and children. The latter samples were obtained at surgery. The activities for succinate dehydrogenase and phosphofructokinase were chosen as markers for mitochondrial and cytoplasmatic enzymes respectively. Glycogen, triglyceride and phosphagen levels were studied. Water and protein content of the muscle tissue undergo continuous changes during foetal life and were therefore also included in the study. The SDH activity was low during gestation and reached a value of 2-3 mmoles/kg w.wt. X min at delivery. The PFK activity was also low during gestation, but around 25 weeks gestation a value of 3-4 mmoles/kg w.wt. X min was common, and around delivery time about 7 mmoles/kg w.wt. X min. At 1-5 years the PFK activity was around 11-12 mmoles/kg w.wt. X min, which is similar to adult muscles. Glycogen content varied, but increased during gestation. In the last trimester of gestation a value of 62-92 mmoles units/kg w.wt. was found. The triglyceride content at the end of the gestation time was 3-16 mmoles glycerol/kg w.wt. The phosphagen levels were quite low all through foetal life, averaging between 0.5 and 3 mmoles/kg for ATP and CP concentrations.

Adenosine Triphosphate↗
PubMed1980

Neuromuscular transmission in the athymic nude mouse.

No major differences were observed in the mechanical properties of diaphragm, extensor digitorum longus and soleus muscles from athymic nude and control mice. Denervated soleus muscles from nudes and controls showed no significant differences in their sensitivities to the cholinoceptor agonists acetylcholine and carbachol, either in the absence or presence of the anticholinesterase, physostigmine, suggesting that postjunctional receptor function is essentially normal. Phrenic nerve-diaphragm preparations from nudes were less sensitive to the twitch-augmenting effects of neostigmine. No difference in the time course of endplate potentials (epps) between nudes and controls was seen either in the absence or presence of neostigmine. Hence the observed differences in twitch augmentation are unlikely to be due to differences in acetylcholinesterase activity in the two muscles. In normal mice miniature endplate potential (mepp) amplitude decreased and mepp frequency increased with age. These changes were associated with an increase in muscle fibre diameter and a concomitant decrease in membrane resistance. Such changes did not occur in nude mice; thus mepp amplitude remained, high as in young normal muscle. It is suggested that the thymus may play a role in muscle development and that the effects on neuromuscular transmission are secondary to changes in development. In cut diaphragm muscles transmitter reversal potentials in nudes and controls were not different. Although there was no difference in the amplitude of the first epp of a train, or in the immediately releasable acetylcholine store, the quantal content of the first epp, the probability of transmitter release, the total nerve terminal acetylcholine store and the transmitter mobilization rate were all reduced. It is considered probable that all the measurable differences in transmitter release can be explained in terms of the nude muscle fibre diameter being small and being associated with a small nerve terminal size.

Acetylcholine↗
PubMed1987

Excitation-contraction uncoupling in the developing skeletal muscle of the muscular dysgenesis mouse embryo.

The muscular dysgenesis recessive autosomal mutation is characterized by a total lack of muscular contraction and a myofibrillar non-organization. Many abnormalities involved in the excitation-contraction coupling are found in mdg/mdg myotubes: 1) the internal structural organization of the membrane coupling between the sarcoplasmic reticulum (SR) and the transverse (T)-tubule forming the triadic association is defective: the triad number is decreased in the muscle and there are a lack of periodic densities between the SR and T-tubule apposed membranes. 2) the voltage-dependent Ca2+ channel contents, identified by binding with the specific blocker PN 200-110, are decreased. The two fast (30 ms) and slow (100 ms) Ca2+ currents present in normal myotubes are absent in mdg/mdg myotubes in vitro. 3) the Ca2+-dependent K+ conductance triggering an action potential followed by a long lasting after hyperpolarization (ahp) is absent in mdg/mdg myotubes. This indicates a lack of the free intracellular Ca2+ increased by the action potential. These results suggest that: 1) the lack of differentiated triadic junctions is directly correlated with very low amounts of voltage-dependent Ca2+ channels; 2) the low amount of Ca2+ channels results directly in decreased Ca2+ currents; 3) the decreased Ca2+ currents are the consequence of the low intracellular Ca2+ concentration which is not sufficient to trigger a contraction. However, the addition of normal motoneurones to mdg/mdg myotubes in culture induces, few days later, an increase in Ca2+ currents.

Animals↗
PubMed2002

Imperatoxin a enhances Ca(2+) release in developing skeletal muscle containing ryanodine receptor type 3.

Most adult mammalian skeletal muscles contain only one isoform of ryanodine receptor (RyR1), whereas neonatal muscles contain two isoforms (RyR1 and RyR3). Membrane depolarization fails to evoke calcium release in muscle cells lacking RyR1, demonstrating an essential role for this isoform in excitation-contraction coupling. In contrast, the role of RyR3 is unknown. We studied the participation of RyR3 in calcium release in wild type (containing both RyR1 and RyR3 isoforms) and RyR3-/- (containing only RyR1) myotubes in the presence or absence of imperatoxin A (IpTxa), a high-affinity agonist of ryanodine receptors. IpTxa significantly increased the amplitude and the rate of release only in wild-type myotubes. Calcium currents, recorded simultaneously with the transients, were not altered with IpTxa treatment. [(3)H]ryanodine binding to RyR1 or RyR3 was significantly increased in the presence of IpTxa. Additionally, IpTxa modified the gating and conductance level of single RyR1 or RyR3 channels when studied in lipid bilayers. Our data show that IpTxa can interact with both RyRs and that RyR3 is functional in myotubes and it can amplify the calcium release signal initiated by RyR1, perhaps through a calcium-induced mechanism. In addition, our data indicate that when RyR3-/- myotubes are voltage-clamped, the effect of IpTxa is not detected because RyR1s are under the control of the dihydropyridine receptor.

Animals↗
PubMed1995

Complete primary structure of chicken cardiac C-protein (MyBP-C) and its expression in developing striated muscles.

C-protein (MyBP-C) is a myosin binding protein of about 140 kDa which is known to modulate myosin assembly in striated muscles. A cardiac-type isoform of C-protein appears not only in cardiac muscle but also in skeletal muscle before skeletal muscle-type isoforms become detectable during myogenesis, suggesting that the cardiac isoform is involved in the early phase of myofibrillogenesis (Bähler et al., 1985; Kawashima et al., 1986). In this study, in order to understand the structure and functional domains of the cardiac-type C-protein, we cloned and sequenced full-length cDNAs encoding chicken cardiac C-protein from lambda gt11 cDNA libraries which were prepared with poly (A)+ RNA from embryonic chicken cardiac muscle as well as embryonic chicken skeletal muscle by using antibodies specific for cardiac C-protein. Two cDNA variants, probably generated by alternative RNA splicing and encoding different C-protein isoforms, were detected. As judged by the cDNA sequences determined, overall homology of the peptide sequence between cardiac and skeletal muscle C-proteins (Einheber et al., 1990; Fürst et al., 1992, Weber et al., 1994) was about 50-55%. Like other myosin binding proteins, skeletal C-proteins, 86 kDa protein and M-protein, cardiac C-protein contains several copies of fibronectin type III motifs and immunoglobulin C2 motifs in the molecule, but their number and arrangements differed somewhat from those in the other proteins. Northern blot analysis with the cloned cDNA as a probe demonstrated that mRNA of 5.0 kb is transcribed in both cardiac and embryonic skeletal muscle, and that it is specifically expressed in cardiac muscle among adult tissues.

Amino Acid Sequence↗
PubMed1989

Cytokeratin expression in experimental murine rhabdomyosarcomas. Intermediate filament pattern in original tumors, allotransplants, cell culture and re-established tumors from cell culture.

Soft tissue sarcomas were induced by 20-methylcholanthrene in NMRI-mice. The tumors were characterized as rhabdomyosarcomas by light and electron microscopy as well as immunohistochemistry (vimentin, desmin and myoglobin expression). Cytokeratins could be demonstrated by a panel of different poly- and monoclonal antibodies in original rhabdomyosarcomas, their allotransplants and the re-established tumors from cell culture in nude mice. The cytokeratin positive tumor cells were arranged in small clusters and/or haphazardly single dispersed in the rhabdomyosarcomas. By means of monoclonal antibodies cytokeratins No. 8 and No. 19 could be evidenced and cytokeratin No. 18 could be made probably. Behind the background of cytokeratin expression in developing fetal cross striated muscle cells our findings are discussed as a reminiscence of embryonal muscle development in these tumors. The significance of cytokeratin expression in rhabdomyosarcomas for diagnostic histopathology is emphasized.

Animals↗
PubMed2005

Developing skeletal muscle cells express functional muscarinic acetylcholine receptors coupled to different intracellular signaling systems.

This study analyzed the expression of muscarinic acetylcholine receptors (mAChRs) in the rat cultured skeletal muscle cells and their coupling to G protein, phospholipase C and adenylyl cyclase (AC). Our results showed the presence of a homogeneous population of [(3)H]methyl-quinuclidinyl benzilate-binding sites in the membrane fraction from the rat cultured muscle (K(D) = 0.4 nM, B(max) = 8.9 fmol mg protein(-1)). Specific muscarinic binding sites were also detected in denervated diaphragm muscles from adult rats and in myoblasts isolated from newborn rats. Activation of mAChRs with carbachol induced specific [(35)S]GTPgammaS binding to cultured muscle membranes and potentiated the forskolin-dependent stimulation of AC. These effects were totally inhibited by 0.1-1 microM atropine. In addition, mAChRs were able to stimulate generation of diacylglycerol (DAG) in response to acetylcholine, carbachol or selective mAChR agonist oxotremorine-M. The carbachol-dependent increase in DAG was inhibited in a concentration-dependent manner by mAChR antagonists atropine, pirenzepine and 4-DAMP mustard. Finally, activation of these receptors was correlated with increased synthesis of acetylcholinesterase, via a PKC-dependent pathway. Taken together, these results indicate that expression of mAChRs, coupled to G protein and distinct intracellular signaling systems, is a characteristic of noninnervated skeletal muscle cells and may be responsible for trophic influences of acetylcholine during formation of the neuromuscular synapse.

Acetylcholine↗