Expression of SERCA2a is not regulated by calcineurin or upon mechanical unloading in skeletal muscle regeneration

This study investigates to what extent the expression of the slow myosin heavy chain (MyHCI) isoform and the slow type sarcoplasmic reticulum Ca2+ ATPase (SERCA2a) isoform are co-regulated in fibers of regenerating skeletal soleus muscle. Both overexpression of cain, a calcineurin inhibitor, or partial tenotomy prevented the expression of MyHCI but left SERCA2a expression unaffected in fibers of regenerating soleus muscles. These data complement those from different experimental models and clearly show that the expression of MyHCI and SERCA2a--the major proteins mediating, respectively, the slow type of contraction and relaxation--are not coregulated in regenerating soleus muscle.     

戊巴比妥对大鼠骨胳肌辣根过氧化物酶(HRP)的轴突摄取和逆行传送作用

腓肠肌内注射HRP后,用生物化学法测定坐骨神经、L_(4-6)节段背根和腹根神经的HRP含量。在戊巴比妥连续全身麻醉大鼠的HRP含量明显低于不麻醉的大鼠,而肌肉不活动(TTX中毒和切腱)大鼠神经组织中的HRP含量无甚变化。刺激神经不能改变麻醉大鼠的HRP含量。上述结果提示:除麻醉剂造成的肌肉不活动因素外,戊巴比妥对大鼠骨胳肌HRP的轴突摄取和逆行传送具有另外的抑制作用。已有研究报道:破伤风和单纯性疱疹病毒脑炎都是由于它们的毒素或病毒,通过外周神经摄取然后逆行传送到各级中枢而致病的。     

Effects of aging on the lateral transmission of force in rat skeletal muscle

The age-related reduction in muscle force cannot be fully explained by the loss of muscle fiber mass or degeneration of myofibers. Our previous study showed that changes in lateral transmission of force could affect the total force transmitted to the tendon. The extracellular matrix (ECM) of skeletal muscle plays an important role in lateral transmission of force. The objective of this study was to define the effects of aging on lateral transmission of force in skeletal muscles, and explore possible underlying mechanisms. In vitro contractile tests were performed on extensor digitorum longus (EDL) muscle of young and old rats with series of tenotomy and myotomy. We concluded that lateral transmission of force was impaired in the old rats, and this deficit could be partly due to increased thickness of the ECM induced by aging.     

Regulation of Taurine Transport in Rat Skeletal Muscle

Taurine concentration of soleus muscle (SL, slow-twitch) was initially about twofold higher than that of extensor digitorum longus muscle (EDL, fast-twitch). Taurine concentration in gastrocnemius muscle (GC) was intermediate between that of EDL and SL. Four days after sciatic nerve section, taurine concentration in the EDL but not in the SL was increased by 2.5-fold. The increase was not due to the muscle atrophy and was observed 28 days after denervation. Tenotomy did not increase the total taurine content of the EDL. The increase in taurine concentration of the denervated EDL was prevented by simultaneous ingestion of guanidinoethane sulfonate, a competitive inhibitor of taurine transport. The initial and the maximal rates of [3H]taurine uptake were significantly higher in SL than in EDL. Denervation dramatically accelerated the initial and the maximal rates of the transport in EDL, whereas it significantly reduced those in SL. In contrast, the electrical stimulation of sciatic nerve accelerated the uptake of taurine by EDL and SL of the control but not of the curare-treated rats. These results suggest that transport of taurine into rat skeletal muscles is regulated differently by neural information and by muscular activity, and that the regulation is dependent on the muscle phenotype.     

Cell proliferation in skeletal muscle following denervation or tenotomy

Summary Autoradiographic experiments using ³H-thymidine were designed to analyse cell proliferation which occurs in skeletal muscle after denervation and after tenotomy. In mouse tibialis anterior and tongue muscles during the first 24 h after denervation or tenotomy labelling levels were low and did not differ significantly from sham operated control muscles. By 48 h after denervation and tenotomy of tibialis anterior muscles, increased levels of labelling occurred in both muscle and connective tissue nuclei. Daily pulse labelling for 7 days after denervation produced a labelling level which was 8 times that of sham operated controls, 25–30% of the total nuclear population being labelled. Denervated muscles had twice the level of labelling compared to tenotomised muscles. These results provide conclusive evidence that both denervation and tenotomy stimulate cell proliferation in skeletal muscle and it is suggested that the increased numbers of labelled muscle nuclei are likely to be the result of mitotic activity in muscle satellite cells.     

Effect of denervation and tenotomy on slow and fast muscles of the chicken

Summary Changes of muscle weights, fiber diameters and ultrastructure were studied in the slow anterior latissimus dorsi (ALD) and in the fast posterior latissimus dorsi (PLD) of the chick three weeks after denervation and tenotomy, and after combined denervation and tenotomy of the two muscles.The slow ALD muscle becomes hypertrophic after denervation (Feng, Jung and Wu, 1962). Three weeks after nerve section, wet weights of ALD muscles are increased by 60% and fiber diameters become by 30% larger than those of contralateral control muscles. In spite of this hypertrophy, degenerative changes are seen in the ultrastructure, similar to those described in denervated atrophic muscles. Areas of dedifferentiation with autophagic vacuoles and aggregates of tubules are found in superficial layers of some fibers. Disintegration of Z lines and filaments along one or two sarcomeres occurs in a number of myofibrils, especially in muscles of young animals.In contrast to denervation alone, simultaneous denervation and tenotomy of the ALD muscles results in atrophy. Decrease of muscle weights and reduction of fiber diameters are similar as after tenotomy; in both cases muscle fibers waste by degeneration and atrophy of myofibrils.The fast PLD muscles underwent extensive atrophy in all three series of experiments. Corresponding atrophic and degenerative changes of ultrastructure were found in all instances.The authors wish to acknowledge gratefully the skillful technical assistance of Mrs. M. Sobotková and Ing. M. Doubek, and editorial assistance of Miss Virginia Hamilton.     

Structural changes in locust leg muscle fibres in response to tenotomy and joint immobilization

Tenotomy and immobilization at minimum physiological length resulted in degenerative changes in the ultrastructure of the locust metathoracic flexor tibiae muscle.Degeneration was observed in some muscle fibres 9 days after tenolomy and was progressive, affecting an increasing proportion of fibres at longer times after operation. Changes included disruption and loss of myofilaments, Z-disk streaming, degeneration of sarcoplasmic reticulum, formation of large membranous complexes and changes in number and appearance of mitochondria. Different muscle fibres followed different degenerative pathways. By 73 days very few intact muscle fibres remained.Joint immobilization resulted in similar but much less severe progressive degeneration. Degenerate fibres were largely localized in the distal and medial parts of the muscle. Both immobilized and tenotomized muscles were invaded by large numbers of fat body cells in the later stages of degeneration.Nerve terminals on degenerate tenotomized and immobilized muscle fibres were ultrastructurally normal. Tendinous cells attaching degenerate muscle fibres to the cuticle themselves degenerated.