scholarly journals Ultrastructure of acetylcholine receptor clusters on cultured muscle fibers.

1976 ◽  
Vol 69 (2) ◽  
pp. 501-507 ◽  
Author(s):  
Z Vogel ◽  
M P Daniels
Keyword(s):  
Skeletal Muscle ◽  
Acetylcholine Receptor ◽  
Muscle Fibers ◽  
The Other ◽  
Immunoperoxidase Staining ◽  
High Concentration ◽  
Receptor Clusters ◽  
Ach Receptors

The structure of regions with a high concentration of ACh receptors (clusters) on cultured skeletal muscle myotubes was examined by immunoperoxidase staining of bound alphaBT. The clusters did not appear to differ from the other regions except in their higher concentration of receptor.

scholarly journals Defective Acetylcholine Receptor Subunit Switch Precedes Atrophy of Slow-Twitch Skeletal Muscle Fibers Lacking ERK1/2 Kinases in Soleus Muscle

2016 ◽  
Vol 6 (1) ◽  
Author(s):  
Shuo Wang ◽  
Bonnie Seaberg ◽  
Ximena Paez-Colasante ◽  
Mendell Rimer
Keyword(s):  
Skeletal Muscle ◽  
Acetylcholine Receptor ◽  
Soleus Muscle ◽  
Muscle Fibers ◽  
Neuromuscular Synapse ◽  
Fiber Morphology ◽  
Skeletal Muscle Fibers ◽  
Slow Twitch

Abstract To test the role of extracellular-signal regulated kinases 1 and 2 (ERK1/2) in slow-twitch, type 1 skeletal muscle fibers, we studied the soleus muscle in mice genetically deficient for myofiber ERK1/2. Young adult mutant soleus was drastically wasted, with highly atrophied type 1 fibers, denervation at most synaptic sites, induction of “fetal” acetylcholine receptor gamma subunit (AChRγ), reduction of “adult” AChRε, and impaired mitochondrial biogenesis and function. In weanlings, fiber morphology and mitochondrial markers were mostly normal, yet AChRγ upregulation and AChRε downregulation were observed. Synaptic sites with fetal AChRs in weanling muscle were ~3% in control and ~40% in mutants, with most of the latter on type 1 fibers. These results suggest that: (1) ERK1/2 are critical for slow-twitch fiber growth; (2) a defective γ/ε-AChR subunit switch, preferentially at synapses on slow fibers, precedes wasting of mutant soleus; (3) denervation is likely to drive this wasting, and (4) the neuromuscular synapse is a primary subcellular target for muscle ERK1/2 function in vivo.

scholarly journals Functional interrelationship between calponin and caldesmon

1991 ◽  
Vol 280 (1) ◽  
pp. 33-38 ◽  
Author(s):  
R Makuch ◽  
K Birukov ◽  
V Shirinsky ◽  
R Dabrowska
Keyword(s):  
Skeletal Muscle ◽  
Smooth Muscle ◽  
Atpase Activity ◽  
Smooth Muscle Contraction ◽  
The Other ◽  
High Concentration ◽  
Thin Filaments ◽  
Actomyosin Atpase ◽  
Molar Excess ◽  
Low Concentrations

Calponin and caldesmon, constituents of smooth-muscle thin filaments, are considered to be potential modulators of smooth-muscle contraction. Both of them interact with actin and inhibit ATPase activity of smooth- and skeletal-muscle actomyosin. Here we show that calponin and caldesmon could bind simultaneously to F-actin when used in subsaturating amounts, whereas each one used in excess caused displacement of the other from the complex with F-actin. Calponin was more effective than caldesmon in this competition: when F-actin was saturated with calponin the binding of caldesmon was eliminated almost completely, whereas even at high molar excess of caldesmon one-third of calponin (relative to the saturation level) always remained bound to actin. The inhibitory effects of low concentrations of calponin and caldesmon on skeletal-muscle actomyosin ATPase were additive, whereas the maximum inhibition of the ATPase attained at high concentration of each of them was practically unaffected by the other one. These data suggest that calponin and caldesmon cannot operate on the same thin filaments. CA(2+)-calmodulin competed with actin for calponin binding, and at high molar excess dissociated the calponin-actin complex and reversed the calponin-induced inhibition of actomyosin ATPase activity.

scholarly journals Repression of slow myosin heavy chain 2 gene expression in fast skeletal muscle fibers by muscarinic acetylcholine receptor and Gαq signaling

2003 ◽  
Vol 162 (5) ◽  
pp. 843-850 ◽  
Author(s):  
Theresa Jordan ◽  
Jinyuan Li ◽  
Hongbin Jiang ◽  
Joseph X. DiMario
Keyword(s):  
Gene Expression ◽  
Skeletal Muscle ◽  
Acetylcholine Receptor ◽  
Muscle Fibers ◽  
Muscarinic Acetylcholine Receptor ◽  
Fast Skeletal Muscle ◽  
Muscarinic Acetylcholine ◽  
Fiber Properties ◽  
Skeletal Muscle Fibers ◽  
Slow Myosin Heavy Chain

Gene expression in skeletal muscle fibers is regulated by innervation and intrinsic fiber properties. To determine the mechanism of repression of slow MyHC2 expression in innervated fast pectoralis major (PM) fibers, we investigated the function of the muscarinic acetylcholine receptor (mAchR) and Gαq. Both mAchR and Gαq are abundant in medial adductor (MA) and PM fibers, and mAchR and Gαq interact in these fibers. Whereas innervation of PM fibers was insufficient to induce slow MyHC2 expression, inhibition of mAchR activity with atropine in innervated PM fibers induced slow MyHC2 expression. Increased Gαq activity repressed slow MyHC2 expression to nondetectable levels in innervated MA fibers. Reduced mAchR activity decreased PKC activity in PM fibers, and increased Gαq activity increased PKC activity in PM and MA fibers. Decreased PKC activity in atropine-treated innervated PM fibers correlated with slow MyHC2 expression. These data suggest that slow MyHC2 repression in innervated fast PM fibers is mediated by cell signaling involving mAchRs, Gαq, and PKC.

scholarly journals Effect of agrin on the distribution of acetylcholine receptors and sodium channels on adult skeletal muscle fibers in culture.

1991 ◽  
Vol 115 (3) ◽  
pp. 765-778 ◽  
Author(s):  
M T Lupa ◽  
J H Caldwell
Keyword(s):  
Skeletal Muscle ◽  
Acetylcholine Receptors ◽  
Muscle Fibers ◽  
Postsynaptic Membrane ◽  
Na Channel ◽  
High Concentration ◽  
Achr Cluster ◽  
Adult Skeletal Muscle ◽  
Skeletal Muscle Fibers ◽  
Alpha Bungarotoxin

We used the loose patch voltage clamp technique and rhodamine-conjugated alpha-bungarotoxin to study the regulation of Na channel (NaCh) and acetylcholine receptor (AChR) distribution on dissociated adult skeletal muscle fibers in culture. The aggregate of AChRs and NaChs normally found in the postsynaptic membrane of these cells gradually fragmented and dispersed from the synaptic region after several days in culture. This dispersal was the result of the collagenase treatment used to dissociate the cells, suggesting that a factor associated with the extracellular matrix was responsible for maintaining the high concentration of AchRs and NaChs at the neuromuscular junction. We tested whether the basal lamina protein agrin, which has been shown to induce the aggregation of AChRs on embryonic myotubes, could similarly influence the distribution of NaChs. By following identified fibers, we found that agrin accelerated both the fragmentation of the endplate AChR cluster into smaller patches as well as the appearance of new AChR clusters away from the endplate. AChR patches which were fragments of the original endplate retained a high density of NaChs, but no new NaCh hotspots were found elsewhere on the fiber, including sites of newly formed AChR clusters. The results are consistent with the hypothesis that extracellular signals regulate the distribution of AChRs and NaChs on skeletal muscle fibers. While agrin probably serves this function for the AChR, it does not appear to play a role in the regulation of the NaCh distribution.

scholarly journals Muscle Activity and Muscle Agrin Regulate the Organization of Cytoskeletal Proteins and Attached Acetylcholine Receptor (Achr) Aggregates in Skeletal Muscle Fibers

2001 ◽  
Vol 153 (7) ◽  
pp. 1453-1464 ◽  
Author(s):  
Gabriela Bezakova ◽  
Terje Lømo
Keyword(s):  
Skeletal Muscle ◽  
Acetylcholine Receptor ◽  
Muscle Activity ◽  
Muscle Fibers ◽  
Cytoskeletal Proteins ◽  
Transverse Orientation ◽  
Single Application ◽  
Skeletal Muscle Fibers ◽  
Denervated Muscles ◽  
Electrical Muscle

In innervated skeletal muscle fibers, dystrophin and β-dystroglycan form rib-like structures (costameres) that appear as predominantly transverse stripes over Z and M lines. Here, we show that the orientation of these stripes becomes longitudinal in denervated muscles and transverse again in denervated electrically stimulated muscles. Skeletal muscle fibers express nonneural (muscle) agrin whose function is not well understood. In this work, a single application of ≥10 nM purified recombinant muscle agrin into denervated muscles preserved the transverse orientation of costameric proteins that is typical for innervated muscles, as did a single application of ≥1 μM neural agrin. At lower concentration, neural agrin induced acetylcholine receptor aggregates, which colocalized with longitudinally oriented β-dystroglycan, dystrophin, utrophin, syntrophin, rapsyn, and β2-laminin in denervated unstimulated fibers and with the same but transversely oriented proteins in innervated or denervated stimulated fibers. The results indicate that costameres are plastic structures whose organization depends on electrical muscle activity and/or muscle agrin.

scholarly journals PO-272 Cancer immunotherapy impedes skeletal muscle repair

2018 ◽  
Vol 1 (5) ◽  
Author(s):  
Yuecheng Li ◽  
Chengyi Liu ◽  
Rui Duan
Keyword(s):  
Skeletal Muscle ◽  
T Cells ◽  
Cancer Immunotherapy ◽  
Cd8 T Cells ◽  
Muscle Fibers ◽  
Treg Cells ◽  
The Other ◽  
Control Group ◽  
Muscle Repair ◽  
Injury Group

Objective To observe the difference of the capacity of skeletal muscle repair and the corresponding immune response in melanoma mice treated with cancer immunotherapy after acute skeletal muscle contusion. Methods  96 males C57BL/6 mice were used in this experiment. They were divided into control group and injury group. The control group included normal control group (C group, n = 8), tumor control group (T group, n = 8) and tumor immunotherapy group (A group, n = 8).The skeletal muscle injury group was divided into normal injury group (D group, n = 24), tumor mice injury group (DT group, n = 24) and cancer immunotherapy injury group (DA group, n = 24). B16 cells were injected subcutaneously into the dorsum of C57/BL mice to prepare melanoma mice model. Immunotherapy is the injection of anti CTLA-4 and anti PD-1 antibodies. The model of gastrocnemius muscle contusion was established. At different time points after damage, mice were sacrificed. The gastrocnemius muscle of mice was made into cryosections. After HE staining and Mason staining, the regeneration of skeletal muscle and the healing of fibrotic scar were observed. The expression of CD8 T Cells and Regulatory T Cells (Treg) were detected by immunofluorescence. Results 1.H&E staining of muscle slices at 7 days after injury showed that myofibers in the non-injured muscles are polygonal in shape with peripheral nuclei. Quantitative evaluation of the skeletal muscle in the cancer immunotherapy injury group (DA group) showed that the number of centrally nucleated fibers was significantly lower than that in the other injury groups（D group，DT group）and there was an enlarged interstitial space. Immunotherapy leads to greater muscle degeneration: vacuolated myofibers could be seen. Collagen deposition was detected by Masson trichrome staining, and collagen deposits were found in the injury group. However, the regenerated muscles of the cancer immunotherapy injury group (DA group) showed more collagen deposits than those of the other injury groups（D group，DT group）, no collagen deposits were found in the control group. On 14 day after injury, the density of muscle fibers in the other injury groups（D group，DT group） was higher than that in immunotherapy group (DA group), which was about 1.5 times of that in immunotherapy group (DA group). The other injury groups（D group，DT group） showed a larger proportion of regenerated muscle fibers with different diameters, whereas the cancer immunotherapy injury group (DA group) had fewer regenerated muscle fibers. Compared with the control group, the mice in the other injury groups（D group，DT group）still had a small amount of collagen deposits, the mice in the cancer immunotherapy injury group (DA group) had more collagen deposits. 3.On 21 day after injury, the average diameter on 21 day higher than that on day 7 in the three injury groups. The mean muscle fiber diameter in the other injury groups（D group，DT group） was significantly larger than that in the immunotherapy injury group. In addition, the regenerated muscle fibers in the other injury groups（D group，DT group） showed better organization and basically returned to normal compared with the immunotherapy group (DA group). There were still some collagen deposits in the immunotherapy group (DA group) mice, but no collagen deposits were found in the other injury groups（D group，DT group）mice. 4.Immunofluorescence staining showed that CD8 T cells were continuously expressed and no Treg cells were found in the immunotherapy group (DA group) mice at 7, 14 and 21 days after contusion. In the other injury groups（D group，DT group）, Treg and CD8 T cells were expressed in skeletal muscle tissue adjacent to the regenerated muscle fibers on 7 days. On day 14, a small number of CD8 T cells and a large number of Treg cells infiltrated the damaged muscles. On day 21, almost no CD8 T cells were detected, and Treg cells continued to express. There was no expression of Treg cells and CD8 T cells in the control group. Conclusions Cancer immunotherapy will delay the repair of damaged skeletal muscle and reduce the capacity of skeletal muscle repair and regeneration.  

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