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PubMed1990

[Muscle training by electrostimulation].

Repeated electrical stimulation of skeletal muscles with intact innervation can lead to increased muscular performance. This form of treatment is employed, for example, in atrophy prophylaxis, re-establishment of lost muscular power, and selective strengthening of isolated muscles or muscle groups, and has also been recommended for sport-related performance training. For the most part, it represents an adjuvant measure to active exercise. The selected current forms and stimulation parameters must be oriented to the laws of stimulation physiology. Suitable selection and positioning of electrodes, together with dosage are decisive for the success of treatment. Recent aspects of electrostimulation are so-called fiberspecific electrotraining and the question as to whether the use of certain stimulation frequencies can preferentially be used for phasic or tonic muscle fibers. Electrostimulation of denervated muscles is controversial.

Humans↗
PubMed1980

Studies on structural changes of F-actin and myosin in living, intact and damaged muscle fibres by means of polarized ultraviolet fluorescence microscopy.

By means of polarized ultraviolet fluorescence microscopy the structural changes of F-actin and myosin were discovered at the changing a functional state of a living muscle fibre and during spreading degeneration (Zenker's necrosis). The character of conformational changes of F-actin and myosin at activation, contraction, contracture and rigor is similar, but the number of changed macromolecules depends on a fibre state. At fibre local damage in its morphological intact parts there was found an alternation of zones, reflecting two states unusual for a fibre. During spreading degeneration these states transform into irreversible contracture and then into rigor. Similar changes were observed in muscle fibres obtained from denervated muscles.

Actins↗
PubMed2001

SFRP2 expression in rabbit myogenic progenitor cells and in adult skeletal muscles.

Satellite cells derived from fast- and slow-twitch muscles have different properties in culture. We have used the differential display technique to retrieve genes differentially expressed in fast- and slow-twitch muscle satellite cell cultures. Amongst these genes we have identified, cloned, sequenced and studied the expression in muscle of rabbit secreted frizzled related protein 2 (SFRP2) mRNA, whose importance in cell fate determination has been well documented. It has been shown that SFRP2 is widely expressed in the developing embryo but its expression in the adult is much more restricted. We show that primary cultures of satellite cells from adult rabbit fast- and slow-twitch muscles strongly and differentially express SFRP2 mRNA. Embryonic rabbit muscle cell primary cultures also strongly express SFRP2 mRNA whereas the myoblast C2.7 cell line shows little expression. We also studied SFRP2 mRNA expression in growing, regenerating and denervated muscles. Embryonic rabbit muscles express SFRP2 mRNA but this rapidly falls off after birth. In adult rabbit muscles SFRP2 mRNA is detected within 1 day of either muscle damage or denervation. Thereafter the SFRP2 mRNA expression profiles are different for fast- and slow-twitch muscle. The function of SFRP2 in muscle is unknown but its putative activity as a Wnt antagonist and its precocious expression after muscle damage suggest a role in satellite cell activation.

Aging↗
PubMed2005

Effects of innervation state on Hsp25 content and phosphorylation in inactive rat plantaris muscles.

AIM: Previous reports suggest a role for neuromuscular activity levels and/or connectivity in modulating Hsp25 expression and phosphorylation (pHsp25) in skeletal muscles. However, pHsp25 has only been studied in denervated muscles and/or muscles exposed to high levels of residual neuromuscular activity. Spinal cord isolation (SI) provides a model in which the muscle is exposed to nearly complete inactivity with maintenance of the nerve-muscle connection. To parcel out the roles of innervation state and activity-independent neural factors, we compared Hsp25 and pHsp25 in the plantaris of control (Con), SI, and denervated (Den, inactivity without neural connectivity) rats. METHODS: Hsp25 and pHsp25 protein levels (soluble and insoluble fractions) were measured with Western blot analysis after 1, 3, 8, 14, or 28 days of SI or Den. pHsp25 was normalized to non-pHsp25 at each time point. RESULTS: Hsp25 was unchanged (days 1, 3 and 14) or increased (days 8 and 28) in the soluble fraction, and decreased (day 1) or increased (days 3, 8 and 14) in the insoluble fraction in Den compared with Con rats. pHsp25 was reduced after 1 and 28 days of Den, but near control levels on days 3, 8, and 14 in the soluble fraction. In the insoluble fraction, pHsp25 levels were lower in Den than Con rats on all days. In both fractions, Hsp25 was lower in SI than Con rats. pHsp25 levels were lower in the soluble fraction and higher in the insoluble fraction in SI than Con rats. CONCLUSION: These results suggest that an intact innervation, even in the absence of muscle activation and/or loading, is critical for Hsp25 phosphorylation in the insoluble fraction. However, the time-dependent decrease in Hsp25 with SI suggests a role for minimal levels of muscle activation and/or loading in maintaining Hsp25 expression during sustained inactivity.

Animals↗
PubMed1984

The effect of denervation on mammalian sarcolemmal proteins and glycoproteins.

The effects of surgical denervation on proteins and glycoproteins of sarcolemmal membranes have been investigated using sarcolemmal fractions prepared from mixed rat muscles. Denervation did not cause any gross change in the protein composition but some consistent quantitative changes were detected. Denervation caused a significant increase in the binding of 125I-labeled concanavalin A (ConA), Ricinus communis agglutinin (RCA120), and wheat germ agglutinin (WGA) to intact membranes. This increased binding appears to be brought about by two mechanisms: the synthesis of more binding-sites with the same apparent KD and the unmasking of previously cryptic binding sites. The activity of sialyl-, galactosyl-, and N-acetylglucosaminyltransferases in the sarcolemmal fractions increased, whereas fucosyl-glycoprotein-transferase activity decreased following denervation. Kinetic analysis of the sialyl- and galactosyltransferase activities showed that the change was due to an increase in Vmax with no change in Km. These results are consistent with an increase in the turnover of sarcolemmal glycoproteins following denervation.

Animals↗
PubMed1990

Parasternal and external intercostal muscle shortening during eupneic breathing.

The interosseous external intercostal (EI) muscles of the upper rib cage are electrically active during inspiration, but the mechanical consequence of their activation is unclear. In 16 anesthetized dogs, we simultaneously measured EI (3rd and 4th interspaces) and parasternal intercostal (PA) (3rd interspace) electromyogram and length. Muscle length was measured by sonomicrometry and expressed as a percentage of resting length (%LR). During resting breathing, each muscle was electrically active and shortened to a similar extent. Sequential EI muscle denervation (3rd and 4th interspaces) followed by PA denervation (3rd interspace) demonstrated significant reductions in the degree of inspiratory shortening for each muscle. Mean EI muscle shortening of the third and fourth interspaces decreased from -3.4 +/- 0.5 and -3.0 +/- 0.4% LR (SE) under control conditions to -0.2 +/- 0.2 and -0.8 +/- 0.3% LR, respectively, after selective denervation of each of these muscles (P less than 0.001 for each). After selective denervation of the PA muscle, its shortening decreased from -3.5 +/- 0.3 to +0.6% LR (SE) (P less than 0.001). PA muscle denervation also caused the EI muscle in the third interspace to change from inspiratory shortening of -0.2% to inspiratory lengthening of +0.2% +/- 0.2 (P less than 0.05). We conclude that during eupneic breathing 1) the EI muscles of the upper rib cage, like the PA muscles, are inspiratory agonists and actively contribute to rib cage expansion and 2) PA muscle contraction contributes to EI muscle shortening.

Animals↗
PubMed1977

Effects of long term denervation on smooth muscle of the chicken expansor secundariorum.

Denervation of the expansor secundariorum muscle of the adult and 2 week chicken, by sectioning the brachial plexus, resulted in an approximate twofold increase in dry weight over 8 weeks. Unlike skeletal muscle, no ultrastructural changes were exhibited by the smooth muscle cells for a period of up to 5 months post denervation. No evidence of hypertrophy of the individual muscle cells was observed, but following colchicine treatment a definite increase in the number of mitotic figures was noted within muscle bundles indicating that the increase in dry weight of the expansor muscle is due to hyperplasia of the smooth muscle cells. The results are discussed in relation to in vitro studies of the interaction of sympathetic nerves with smooth muscle.

Animals↗