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At least 433 records · Page 24Linked to original sources
PubMed1984

Denervated skeletal muscle displays discoordinate regulation for the synthesis of several myofibrillar proteins.

Synthesis patterns of myosin heavy- and light-chain isoforms, tropomyosin and troponin, have been studied in chicken fast muscle denervated at both neonatal and adult stages. Denervated neonatal muscle does not synthesize the adult myosin heavy-chain isoform at the time of denervation, but it does synthesize the adult isoform several months after denervation. Thus, innervation does not appear to be necessary for the normal sequential replacement of embryonic and neonatal myosin heavy chain by the adult variant. Nerve is required, however, for the regulation of tropomyosin and troponin expression. Normally the pectoralis major muscle represses synthesis of both beta-tropomyosin and leg-type troponin T during late embryonic development. After denervation, however, the muscle relaxes its ongoing repression of these proteins and significant amounts of both beta-tropomyosin and leg-type troponin T are synthesized by the muscle. Denervation also results in an altered pattern of myosin light-chain synthesis so that the ratio of fast light-chain 3/fast light-chain 1 decreases. Similar results are found in muscle denervated at the adult stage. In denervated muscle, therefore, synthesis of these myofibrillar proteins is not coordinated: ongoing isoform shifts proceed to express an adult pattern of myosin heavy chain while tropomyosin, troponin, and myosin light-chain patterns appear to revert to embryonic configurations.

Aging↗
PubMed2001

Altered balance of proteinase inhibitors in atrophic muscle after denervation.

Skeletal muscle denervation leads to an increase of proteolytic activity, which is also favoured by reduced levels of alpha1 antichymotrypsin and nexin II, two serine-proteinase inhibitors normally acting at the neuromuscular junction. In the present experiments we extended our investigation to other muscular proteinase inhibitors after denervation. In all muscles examined (soleus, plantaris, extensor digitorum longus) specific immunoreactivity for alpha2macroglobulin (alpha2M) and alpha1proteinase inhibitor (alpha-1-antitrypsin, ATI) was distributed in peri-endomysial structures as well as in small patches inside the fibres. By contrast, inter-alpha-trypsin inhibitor (ITI) was mainly localized in the extracellular matrix. These localization patterns did not change substantially in 15-days denervated muscles. Dot-blot analysis revealed a small decrease (about 15%) of alpha2M in 15-days denervated muscles, while ATI and ITI specific activities were substantially unchanged. RT-PCR allowed us to detect the above protease inhibitor mRNAs in normal muscle homogenates. Denervation atrophy induced by section of the sciatic nerve resulted in a remarkable reduction of (2macroglobulin mRNA (60%) and ITI (30%), but not ATI, as measured by computer-assisted semiquantitative densitometry of electrophoresed RT-PCR bands. The marked decrease of alpha2M we have detected in denervated muscle may be responsible, at least in part, for the proteolytic increase which is known to occur in skeletal muscle during denervation atrophy.

Alpha-Globulins↗
PubMed1996

Natural killer cells and macrophages in immature denervated rat muscles.

Neonatally denervated muscle fibers of rat atrophy, degenerate, and eventually vanish unless they are reinnervated. Immunohistochemistry of hindlimb muscles denervated for 4 to 8 weeks showed OX8+ and also 3.2.3+ natural killer (NK) cells and ED1+ macrophages, which were much more frequent between atrophic non-reinnervated fibers than between reinnervated fibers. OX19+ T cells and OX33+ B cells were rare. Electron micrographs 4 to 15 weeks after denervation showed typical medium-sized lymphocytes and large lymphocytes with dense granules in close contact with muscle fibers of 1 to 3 micrometer diameter. Blunt projections of lymphocytes penetrated the basal lamina of the muscle fibers and established membrane contacts. The basal lamina of atrophic fibers had been invaded by slender projections of cytoplasm-rich stellate or fusiform cells, which seemed to strip them of their basal lamina. Thin fibers without basal lamina were engulfed by the stellate cells that in several aspects resembled fibrocytes but that presumably corresponded to the ED1+ macrophages seen by light microscopy. Electron microscopy and in situ nick translation demonstrated the rare appearance of apoptotic myonuclei. It is suggested that lymphocytes and macrophages are involved in the breakdown of neonatally denervated muscle fibers, and that apoptosis following contact with NK cells may represent the mode of cell death.

Animals↗
PubMed1981

Characteristics of sarcoplasmic reticulum from normal and denervated rat skeletal muscle.

Denervation of rat skeletal muscle produces after 14 days a decrease in Ca2+ uptake of a heterogeneous population of sarcoplasmic-reticulum vesicles, when measured in the presence of oxalate. The Mg2+-dependent ATPase (Ca2+-independent) activity increased after the same period and the Ca2+ + Mg2+-dependent ATPase activity decreased. Concomitant with these changes, there was an increase in vesicle size and calcium content. The observations are discussed in terms of changes in altered membrane structure, manifested in the shift of the equilibrium of the ATPase from an enzyme involved in calcium transport to a phosphoenzyme giving rise to an increase in the Mg2+-dependent ATPase activity.

Adenosine Triphosphatases↗