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Extensor Digitorum Longus Muscle (extensor + digitorum_longu_muscle)
Selected AbstractsCapsaicin delays regeneration of the neuromuscular junction of rat extensor digitorum longus muscle after ischemiaMUSCLE AND NERVE, Issue 4 2006Béla Turchányi MD Abstract Trauma or the tourniquet used in orthopedic surgery is often associated with ischemia,reperfusion (I/R) injury with a consequent decrease of muscle power. To explore whether components of the neuromuscular junction (NMJ) are involved in this muscle dysfunction, NMJs were ultrastructurally characterized in the extensor digitorum longus muscle of rats at reperfusion times of 1, 24, 72, and 168 h after a 120-min arterial occlusion. Disorganization of the presynaptic membrane and mitochondrial injury was noted at 1 h, followed by fragmentation and partial engulfment of nerve terminals by Schwann cells at 24 and 72 h. The magnitude of degenerative changes declined at 168 h, suggesting the commencement of regeneration. The postsynaptic membrane remained intact throughout the whole period. In our previous study, deafferentation with pretreatment of the sciatic nerve with capsaicin, which reduces neurogenic inflammation and has a selective effect on nociceptive fibers, improved functional recovery of the muscle after I/R. The present results document a significantly delayed structural regeneration of the motor nerve terminals after combined capsaicin and I/R treatment. Since capsaicin treatment alone had no discernible effect on the structure of NMJs, the findings point to a possibly indirect effect of capsaicin on the motor nerves, which may predispose them to increased susceptibility unmasked only by a subsequent injury. The mismatch between the enhanced functional improvement of the muscle and delayed regeneration of the nerve after capsaicin pretreatment questions the efficient use of such deafferentation to protect the integrity of neuromuscular junctions in I/R injury. Muscle Nerve, 2006 [source] Effects of chlorpromazine on excitation,contraction coupling events in fast-twitch skeletal muscle fibres of the ratBRITISH JOURNAL OF PHARMACOLOGY, Issue 4 2004R Wagner Single mechanically skinned fibres from the rat extensor digitorum longus muscle, which allow access to intracellular compartments, were used to examine the effects of 0.5,100 ,M chlorpromazine hydrochloride (CPZ) on the major steps of the excitation,contraction (E,C) coupling to elucidate the involvement of skeletal muscle in the neuroleptic malignant syndrome (NMS). At 1 ,M, CPZ caused a 20,30% increase in the force response induced by t-system depolarisation and a marked increase in the rate of caffeine-induced SR Ca2+ release. At [CPZ]2.5 ,M, there was an initial increase followed by a marked decrease of the t-system depolarisation-induced force responses, while the potentiating effect on the caffeine-induced SR Ca2+ release remained. These effects were reversible. CPZ had no effect on the maximum Ca2+ -activated force, but caused reversible, concentration-dependent increases in the Ca2+ sensitivity of the contractile apparatus at [CPZ] 10 ,M, with a 50% predicted shift of 0.11 pCa (,log [Ca2+]) units at 82.3 ,M CPZ. CPZ did not alter the rate of SR-Ca2+ loading at 1 and 10 ,M, but reversibly reduced it by ,40% at 100 ,M by reducing the SR Ca2+ pump. Nevertheless, the SR Ca2+ content was greater when fibres became unresponsive to t-system-induced depolarisation in the presence than in the absence of 100 ,M CPZ. The results show that CPZ has concentration-dependent stimulatory and inhibitory effects on various steps of the E,C coupling, which can explain the involvement of skeletal muscle in NMS and reconcile previous divergent data on CPZ effects on muscle. British Journal of Pharmacology (2004) 141, 624,633. doi:10.1038/sj.bjp.0705655 [source] Synthesis and degradation of type IV collagen in rat skeletal muscle during immobilization in shortened and lengthened positionsACTA PHYSIOLOGICA, Issue 4 2003A. M. Ahtikoski Abstract Aim:, Type IV collagen is a major protein in basement membranes surrounding and supporting skeletal muscle cells. In the present study, we tested the hypotheses that immobilization down-regulates synthesis and up-regulates degradation of type IV collagen in skeletal muscle. Methods:, mRNA level and concentration of type IV collagen as well as mRNA levels and activities of proteins involved in its degradation were analysed from soleus (SOL), gastrocnemius (GAS) and extensor digitorum longus muscles after immobilization in shortened and lengthened positions for 1, 3 and 7 days. Results:, Following immobilization, type IV collagen mRNA level was decreased in SOL and GAS suggesting down-regulated synthesis of this protein. The mRNA level and activity of matrix metalloproteinase-2 (proMMP-2) were increased in all muscles, while the activity of tissue inhibitor of metalloproteinase-2 was decreased in SOL and GAS. These findings reflect an increased capacity for degradation of type IV collagen. Conclusions: As a consequence of decreased synthesis/degradation ratio immobilization reduced the concentration of type IV collagen in all muscles. The regulation of type IV collagen through synthesis and/or degradation seems, however, to be muscle specific. Immobilization in lengthened position seems to delay and partly decrease the net degradation of type IV collagen. [source] Comparison of the myoplasmic calcium transient elicited by an action potential in intact fibres of mdx and normal miceTHE JOURNAL OF PHYSIOLOGY, Issue 21 2008Stephen Hollingworth The myoplasmic free [Ca2+] transient elicited by an action potential (,[Ca2+]) was compared in fast-twitch fibres of mdx (dystrophin null) and normal mice. Methods were used that maximized the likelihood that any detected differences apply in vivo. Small bundles of fibres were manually dissected from extensor digitorum longus muscles of 7- to 14-week-old mice. One fibre within a bundle was microinjected with furaptra, a low-affinity rapidly responding fluorescent calcium indicator. A fibre was accepted for study if it gave a stable, all-or-nothing fluorescence response to an external shock. In 18 normal fibres, the peak amplitude and the full-duration at half-maximum (FDHM) of ,[Ca2+] were 18.4 ± 0.5 ,m and 4.9 ± 0.2 ms, respectively (mean ±s.e.m.; 16°C). In 13 mdx fibres, the corresponding values were 14.5 ± 0.6 ,m and 4.7 ± 0.2 ms. The difference in amplitude is statistically highly significant (P= 0.0001; two-tailed t test), whereas the difference in FDHM is not (P= 0.3). A multi-compartment computer model was used to estimate the amplitude and time course of the sarcoplasmic reticulum (SR) calcium release flux underlying ,[Ca2+]. Estimates were made based on several differing assumptions: (i) that the resting myoplasmic free Ca2+ concentration ([Ca2+]R) and the total concentration of parvalbumin ([ParvT]) are the same in mdx and normal fibres, (ii) that [Ca2+]R is larger in mdx fibres, (iii) that [ParvT] is smaller in mdx fibres, and (iv) that [Ca2+]R is larger and [ParvT] is smaller in mdx fibres. According to the simulations, the 21% smaller amplitude of ,[Ca2+] in mdx fibres in combination with the unchanged FDHM of ,[Ca2+] is consistent with mdx fibres having a ,25% smaller flux amplitude, a 6,23% larger FDHM of the flux, and a 9,20% smaller total amount of released Ca2+ than normal fibres. The changes in flux are probably due to a change in the gating of the SR Ca2+ -release channels and/or in their single channel flux. The link between these changes and the absence of dystrophin remains to be elucidated. [source] Distribution of Rest Periods Between Electrically Generated Contractions in Denervated Muscles of RatsARTIFICIAL ORGANS, Issue 6 2005Douglas E. Dow Abstract:, Stimulation protocols for denervated muscles distribute the generated contractions either within treatment sessions followed by hours of rest, or repeated 24 h per day with each contraction followed by a constant interval of rest. Our purpose was to directly compare the effects of the same number of identically generated contractions having different temporal daily distributions. For 5 weeks in denervated extensor digitorum longus muscles of rats, between 100 and 800 contractions were generated daily, distributed either within worksets that alternated periods of activity and rest, or separated by constant intervals of rest. Most of the tested protocols maintained muscle mass and maximum force near values of innervated controls. Although 100 contractions daily generated at constant intervals were sufficient to maintain mass and force, 100 contractions during a 4-h treatment session followed by 20 h of rest were not sufficient, and mass and force were not different from values of denervated muscles. [source] | |||||||||||||