scholarly journals Non-myotendinous force transmission in rat extensor digitorum longus muscle

1998 ◽  
Vol 201 (5) ◽  
pp. 683-691 ◽  
Author(s):  
P Huijing ◽  
G C Baan ◽  
G T Rebel
Keyword(s):  
Extensor Digitorum Longus ◽  
Force Production ◽  
Muscle Length ◽  
Length Change ◽  
Extensor Digitorum Longus Muscle ◽  
Extensor Digitorum ◽  
Force Transmission ◽  
Cross Sectional ◽  
Longus Muscle ◽  
Intact Muscle

The extensor digitorum longus muscle (EDL) of the rat hindleg consists of four heads. The heads are named after their insertions on the digits of toes II, III, IV and V. The EDL heads share a proximal tendon and aponeurosis, but have separate distal aponeuroses and tendons. By cutting the distal tendons of selected heads, direct myotendinous force transmission within these heads is prevented. Therefore, force exerted by the muscle would be expected to decrease according to the physiological cross-sectional area disconnected if myotendinous force transmission were the only mechanism of force transmission. <P> The results indicate that EDL force production remained at high levels after acute tenotomy: muscle length-force curves did not alter significantly following cutting of the tendons of heads II and III. Cutting the tendon of head IV as well leaves only head V in its original condition. After tenotomy of head IV, length-force characteristics were altered significantly, but optimum force was maintained at 84 % of that of the intact muscle. After separation of head IV from head V intramuscularly for some distance along their interface, the force dropped to much lower levels, with optimum force approaching 50 % of that of the intact muscle. <P> The length of active proximal fibres (located within head II) did not remain constant but increased with increasing muscle lengths after tenotomy as well as after partial separation of heads IV and V. The amount of length change decreased after intramuscular separation of the heads, indicating declining reactive forces. <P> It is concluded that force transmission occurred from tenotomized heads to their intact neighbours and <I>vice versa</I>. The magnitude of the force transmitted from head to head was dependent on the degree of integrity of the connective tissue at the interface between heads. <P>

scholarly journals Alpha 7 integrin preserves the function of the extensor digitorum longus muscle in dystrophin-null mice

2013 ◽  
Vol 115 (9) ◽  
pp. 1388-1392 ◽  
Author(s):  
Chady H. Hakim ◽  
Dean J. Burkin ◽  
Dongsheng Duan
Keyword(s):  
Muscular Dystrophy ◽  
Knockout Mice ◽  
Muscle Function ◽  
Extensor Digitorum Longus ◽  
Transmission Loss ◽  
Extensor Digitorum Longus Muscle ◽  
Extensor Digitorum ◽  
Force Transmission ◽  
Double Knockout ◽  
Longus Muscle

The dystrophin-associated glycoprotein complex (DGC) and the α7β1-integrin complex are two independent protein complexes that link the extracellular matrix with the cytoskeleton in muscle cells. These associations stabilize the sarcolemma during force transmission. Loss of either one of these complexes leads to muscular dystrophy. Dystrophin is a major component of the DGC. Its absence results in Duchenne muscular dystrophy (DMD). Because α7-integrin overexpression has been shown to ameliorate muscle histopathology in mouse models of DMD, we hypothesize that the α7β1-integrin complex can help preserve muscle function. To test this hypothesis, we evaluated muscle force, elasticity, and the viscous property of the extensor digitorum longus muscle in 19-day-old normal BL6, dystrophin-null mdx4cv, α7-integrin-null, and dystrophin/α7-integrin double knockout mice. While nominal changes were found in single knockout mice, contractility and passive properties were significantly compromised in α7-integrin double knockout mice. Our results suggest that DGC and α7β1-integrin complexes may compensate each other to maintain normal skeletal muscle function. α7β1-Integrin upregulation may hold promise to treat not only histological, but also physiological, defects in DMD.

Potentiation of in vitro concentric work in mouse fast muscle

1998 ◽  
Vol 84 (1) ◽  
pp. 236-243 ◽  
Author(s):  
R. W. Grange ◽  
R. Vandenboom ◽  
J. Xeni ◽  
M. E. Houston
Keyword(s):  
Extensor Digitorum Longus ◽  
Conditioning Stimulus ◽  
Muscle Length ◽  
Extensor Digitorum Longus Muscle ◽  
Extensor Digitorum ◽  
Fast Muscle ◽  
Phosphate Content ◽  
Longus Muscle

Grange, R. W., R. Vandenboom, J. Xeni, and M. E. Houston.Potentiation of in vitro concentric work in mouse fast muscle. J. Appl. Physiol. 84(1): 236–243, 1998.—Phosphorylation of myosin regulatory light chain (R-LC) is associated with potentiated work and power during twitch afterloaded contractions in mouse extensor digitorum longus muscle [R. W. Grange, C. R. Cory, R. Vandenboom, and M. E. Houston. Am. J. Physiol. 269 ( Cell Physiol. 38): C713–C724, 1995]. We now describe the association between R-LC phosphorylation and potentiated concentric work when the extensor digitorum longus muscle is rhythmically shortened and lengthened to simulate contractions in vivo. Work output (at 25°C) was characterized at sine frequencies of 3, 5, 7, 10, and 15 Hz at excursions of 0.6, 1.2, and 1.6 mm (∼5, 9, and 13% optimal muscle length) at a low level of R-LC phosphorylation. Muscles stimulated during the sine function with a single twitch at specific times before or after the longest muscle length yielded maximal concentric work near the longest muscle length at a sine frequency of 7 Hz (e.g., excursion ∼9% optimal muscle length = 1.6 J/kg). Power increased linearly between sine frequencies of 3 and 15 Hz at all excursions (maximum ∼29 W). After a 5-Hz 20-s conditioning stimulus and coincident with a 3.7-fold increase in R-LC phosphate content (e.g., from 0.19 to 0.70 mol phosphate/mol R-LC), work at the three excursions and a sine frequency of 7 Hz was potentiated a mean of 25, 44, and 50% ( P < 0.05), respectively. The potentiated work during rhythmic contractions is consistent with enhanced interaction between actin and myosin in the force-generating states. On the basis of observations in skinned skeletal muscle fibers (H. L. Sweeney and J. T. Stull. Proc. Natl. Acad. Sci. USA 87: 414–418, 1990), this enhancement could result from increased phosphate incorporation by the myosin R-LC. Under the assumption that the predominant effect of the conditioning stimulus was to increase R-LC phosphate content, our data suggest that a similar mechanism may be evident in intact muscle.

scholarly journals Measurement of Lateral Transmission of Force in the Extensor Digitorum Longus Muscle of Young and Old Mice

2021 ◽  
Vol 22 (22) ◽  
pp. 12356
Author(s):  
Keitaro Minato ◽  
Yuki Yoshimoto ◽  
Tamaki Kurosawa ◽  
Kei Watanabe ◽  
Hiroyuki Kawashima ◽  
...  
Keyword(s):  
Connective Tissue ◽  
Extensor Digitorum Longus ◽  
Lateral Force ◽  
Extensor Digitorum Longus Muscle ◽  
Extensor Digitorum ◽  
Main Function ◽  
Force Transmission ◽  
Longus Muscle ◽  
Lateral Transmission ◽  
Old Mice

The main function of skeletal muscles is to generate force. The force developed by myofiber contraction is transmitted to the tendon. There are two pathways of force transmission from myofibers to tendons: longitudinal transmission that depends on tension elicited via the myotendinous junction and lateral transmission that depends on shear elicited via the interface between the myofiber surface and surrounding connective tissue. Experiments using animal muscle and mathematical models indicated that lateral transmission is the dominant pathway in muscle force transmission. Studies using rat muscle showed that the efficiency of lateral force transmission declines with age. Here, the lateral transmission of force was measured using the extensor digitorum longus muscle from young and old mice. Dependence on longitudinal transmission increased in the old muscle, and there was a trend for lower efficiency of lateral force transmission in the old muscle compared to the young muscle. There was a noticeable increase in the connective tissue volume in the old muscle; however, there was no significant change in the expression of dystrophin, a critical molecule for the link between the myofiber cytoskeleton and extracellular matrix. This study demonstrates the measurement of lateral force transmission in mouse muscles and that alteration in force transmission property may underlie age-related muscle weakness.

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