骨骼肌纤维类型及其细胞与分子基础

骨骼肌纤维类型众多，不同肌组织分布和构成比例不同，以适应其复杂的功能。肌纤维类型及其表达的专一蛋白同功型的多样性，是骨骼肌功能差异和适应性的结构和分子基础。     

骨骼肌的纤维类型及其转变机制

骨骼肌是人体最大的运动器官,纤维类型和蛋白同功型的多样性,以及在不同肌组织中的分布和构成比例,决定其对复杂功能的适应性。随着研究手段的不断改进,人们对骨骼肌纤维亦有更新的认识。     

大鼠骨骼肌纤维组织化学分型与肌球蛋白重链的功能

目的 研究分析了成年SD大鼠外侧腓肠肌各肌亚体内肌纤维的分布与肌球蛋白重链异构体(MHCs)的构成.方法 应用琥珀酸脱氢酶(SDH)组织化学染色分析其4型肌纤维构成比例与横切面积,并以十二烷基硫酸钠-聚丙烯酰胺小孔梯度凝胶电泳(SDS-PAGE)检测肌球蛋白重链异构体.结果 Ⅰ型慢缩氧化(SO型)肌纤维、ⅡX型快缩氧化(FO型)肌纤维、ⅡA型快缩氧化酵解(FOG型)肌纤维及ⅡB型快缩酵解(FG型)肌纤维的构成比例在内侧亚体分别为(10.2±4.1)%、(2.8±2.1)%、(25.7±9.6)%、(61.3±10.1)%;在外侧浅亚体分别为(15.9±8.2)%、(6.1±2.6)%、(22.8±11.5)%、(55.2±12.6)%;而在外侧深亚体则分别为(21.3±9.2)%、(9.8±2.5)%、(18.5±8.7)%、(50.4±10.9)%.4型肌纤维均呈交错式镶嵌型分布.Ⅰ型肌纤维横切面积较小,ⅡX型肌纤维横切面积最小,ⅡA型肌纤维横切面积中等,ⅡB型肌纤维横切面积最大.与使用SDS-PAGE在内侧亚体、外侧浅亚体及外侧深亚体分别发现的肌球蛋白重链异构体(MHCs)所确定的MHCsⅠ、MHCsⅡx(或Ⅱd)、MHCsⅡa、MHCsⅡb相对应.结论 大鼠外侧腓肠肌的重要功能是屈膝关节和伸跗关节,在提踵推进躯体向前和需少量肌力活动时,主要依靠外侧浅、深亚体的肌纤维完成.只有快速运动使肌力需要25%以上时,才有内侧亚体的参与.     

羊髋部和大腿肌组织的肌纤维类型分布

<正> 组成肌肉内肌纤维类型与其运动和姿势的功能有关。作者在本文检测了组成羊的髋部和大腿肌肉的肌纤维类型和不同的分布。分别以肌球蛋白ATP酶和NADH四唑鎓还原酶(NADH——TR)活动把肌纤维分为Ⅰ型,ⅡA和ⅡB型。股中间肌只由Ⅰ型肌纤维组成,这些纤维显示出弱硷稳定肌球蛋白ATP酶和强NADH——TR活性。臀辅     

神经肌肉的电生理检查

神经肌肉疾病的传统诊断主要依据临床症状和体征、各种血液学检验、肌肉活检、电生理和分子基因检查。肌电图和神经传导速度的检查能确定运动单位不同水平的异常,因此能区别肌源性和神经源性疾病。除了传统的肌电图(EMG)检查,还有单纤维肌电图、巨肌电图等。一、EMG的解剖及生理学基础运动单位是肌肉活动的最小单位,肌细胞的收缩依赖肌原纤维。肌原纤维的主要成分是肌红蛋白和肌球蛋白。肌球蛋白能分解成三磷腺苷(ATP)而释放能量,使其收缩做功。(一)肌纤维肌纤维的直径为0.01~0.1cm,长度2cm~12cm之间。它主要由肌膜、肌浆、细胞核和肌原…     

酸性和碱性预孵育处理对骨骼肌肌纤维分型的影响—肌球蛋白ATP酶法

为比较分别经酸性和碱性预孵育液处理的肌球蛋白ATP酶反应法对骨骼肌肌纤维分型的影响．采用酸性（pH4．5）和碱性（pH10．4）预孵育肌球蛋白ATP酶法对大鼠躯干的腹外侧荐尾肌、后肢的处长伸肌相邻切片分别染色，然后比较相邻切片的相同肌纤维类型。结果显示两种预孵育液对ⅡA型肌纤维的分型设有影响，而酸性预孵育液处理后所鉴别的Ⅰ型和ⅡB型肌纤维，在经碱性预孵育液后有少数分别呈现为ⅡB型和ⅡA型肌纤维。本研究表明酸和碱性预孵育ATP酶染色对骨骼肌肌纤维的分型没有完全对应的“镇相”结果，这可能提示肌球蛋白ATP酶的活性在不同的酸性和碱性环境中有不同的稳定性。     

骨骼肌肌纤维生后发育及肌纤维类型的发育

骨骼肌是人体最大的运动器官,骨骼肌的研究一直为人们所关注.骨骼肌是由不同类型的肌纤维组成,且各种类型的肌纤维具有不同的收缩性质.生后发育过程中肌纤维型的构成对骨骼肌的发育是至关重要的.回顾文献,本文就骨骼肌生后发育,肌纤维分型进行综述.     

肩关节周围肌的肌纤维型分布

国内外学者对人类骨骼肌的肌纤维型分布以及肩袖诸肌的大体形态和血管神经分布已有许多研究[1-4],而对国人冈上肌、冈下肌、小圆肌和大圆肌的肌纤维型分布尚未见系统报道.本研究利用肌球蛋白ATP酶组织化学显色法,研究国人冈上肌、冈下肌、小圆肌和大圆肌的肌纤维型分布特点和构成比例,分析各肌的肌纤维型与其功能的相关性.为国人骨骼肌的肌纤维型分布积累基础资料,并为肌运动生理和临床应用提供形态学数据.     

背阔肌的组织化学特征研究

本文用酸碱预孵育肌球蛋白ATP酶法、乳酸脱氢酶法、油红O法、PAS法,研究了20只犬的背阔肌.结果表明,用肌球蛋白ATP酶法可将肌纤维分为Ⅰ型和Ⅱ型.Ⅰ型可分为3个亚型,Ⅱ型可分为ⅡA、ⅡB和ⅡC3个亚型.Ⅱ型肌纤维在背阔肌中占的比例大.Ⅱ型肌纤维含有较多糖原,Ⅰ型肌纤维含有较多脂肪颗粒.通过酶的染色观察,Ⅰ型、ⅡB和ⅡC亚型肌纤维的乳酸脱氢酶活性强弱无明显差别,ⅡA亚型肌纤维乳酸脱氢酶活性较弱.本文对背阔肌组织化学特征进行了讨论.     

低氧高糖条件下家兔骨骼肌Ⅰ型纤维向Ⅱ型纤维转化的作用

目的通过在体外对家兔骨骼肌两型肌纤维细胞进行不同培养方法的摸索和对其标志蛋白MHC同功型变化的检测,探索两型肌纤维细胞间的转化条件。方法运用改良的肌球蛋白ATP酶组织化学染色法对家兔骨骼肌的肌纤维类型进行染色并观察;应用RT-PCR方法检测在不同培养条件下家兔骨骼肌MHC亚型mRNA的表达情况。结果肌组织消化组:固有半膜肌表达MHCⅠ型及少量的MHCⅡ型,副半膜肌表达MHCⅡa和Ⅱb型。细胞培养组:常氧高糖组固有半膜肌表达MHCⅡa和Ⅱb,不表达MHCⅠ型;副半膜肌表达MHCⅡa和Ⅱb,不表达MHCⅠ型;低氧高糖组固有半膜肌表达MHCⅡa和Ⅱb,不表达MHCⅠ型;副半膜肌表达MHCⅡb,不表达MHCⅠ型。结论含15%FBS的常氧高糖培养基适宜骨骼肌细胞生长,并且在低氧高糖条件下,骨骼肌Ⅰ型纤维有向Ⅱ型纤维转化的趋势。     

Effects of hypobaric hypoxia on histochemical fibre-type composition and myosin heavy chain isoform component in the rat soleus muscle

Histochemical fibre-type composition and myosin heavy chain isoform component in the soleus muscle were studied in normoxic rats at postnatal ages of 5, 10, 15, and 20 weeks and in rats exposed to hypobaric hypoxia (460 torr) for 5 weeks from postnatal ages of 5, 10, and 15 weeks. The increase in the percentage of type I fibres and the concomitant decrease in that of type IIa fibres in the soleus muscle of normoxic rats were observed until 15 weeks of age. On the other hand, no change in the fibre-type composition of the muscle during postnatal development was observed in hypoxic rats, irrespective of the age at which they were exposed to hypoxia. The changes in the myosin heavy chain isoform component (MHC I and MHC IIa) of the muscle during postnatal development and by hypoxia corresponded well with those in the muscle fibre-type composition. It is concluded that hypobaric hypoxia inhibits the growth-related shift of muscle fibre-types from type IIa to type I and of myosin heavy chain isoforms from MHC IIa to MHC I in the rat soleus muscle, and that there are no changes in the muscle fibre-type composition or the myosin heavy chain isoform component caused by hypoxia after the shifts in these parameters which occur during postnatal development are completed.     

Segmental Distribution of Myosin Heavy Chain Isoforms Within Single Muscle Fibers

Despite many studies looking at the distribution of myosin heavy chain (MHC) isoforms across a transverse section of muscle, knowledge of MHC distribution along the longitudinal axis of a single skeletal muscle fiber has been relatively overlooked. Immunocytochemistry was performed on serial sections of rat extensor digitorum longus (EDL) muscle to identify MHC types I, IIA, IIX, IIY, and IIB. Sixteen fascicles which contained a total of 362 fibers were randomly and systematically sampled from the three EDL muscles. All MHC type I and type II isoforms were expressed. Segmental expression occurred within a very limited segment. MHC isoform expression followed the accepted traditional order from I?IIA?IIX?IIB, however, in some samples expression of an isoform was circumvented from IIB to I or from I to IIB directly. Segmental distribution of MHC isoforms along a single muscle fiber may be because of the myonuclear domain. Anat Rec, 300:1636–1642, 2017. © 2017 Wiley Periodicals, Inc.     

High‐Intensity Resistance Training with Insufficient Recovery Time Between Bouts Induce Atrophy and Alterations in Myosin Heavy Chain Content in Rat Skeletal Muscle

The aim of this study was to test whether high‐intensity resistance training with insufficient recovery time between bouts, could result in a decrease of muscle fiber cross‐sectional area (CSA), alter fiber‐type frequencies and myosin heavy chain (MHC) isoform content in rat skeletal muscle. Wistar rats were divided into two groups: trained (Tr) and control (Co). Tr group were subjected to a high‐intensity resistance training program (5 days/week) for 12 weeks, involving jump bouts into water, carrying progressive overloads based on percentage body weight. At the end of experiment, animals were sacrificed, superficial white (SW) and deep red (DR) portions of the plantaris muscle were removed and submitted to mATPase histochemical reaction and SDS‐PAGE analysis. Throughout the experiment, both groups increased body weight, but Tr was lower than Co. There was a significant reduction in IIA and IID muscle fiber CSA in the DR portion of Tr compared to Co. Muscle fiber‐type frequencies showed a reduction in Types I and IIA in the DR portion and IID in the SW portion of Tr compared to Co; there was an increase in Types IIBD frequency in the DR portion. Change in muscle fiber‐type frequency was supported by a significant decrease in MHCI and MHCIIa isoforms accompanied by a significant increase in MHCIIb isoform content. MHCIId showed no significant differences between groups. These data show that high‐intensity resistance training with insufficient recovery time between bouts promoted muscle atrophy and a transition from slow‐to‐fast contractile activity in rat plantaris muscle. Anat Rec, 2011. © 2011 Wiley‐Liss, Inc.     

Functional heterogeneity of mammalian single muscle fibres: do myosin isoforms tell the whole story?

The large amount of data published in the last 10-15 years indicate that myosin isoforms are the major determinant of the large functional heterogeneity of the key contractile and biochemical properties of skeletal muscle fibres, including velocity of shortening, ATP consumption and power. Recent evidences are difficult to reconcile with such an idea and suggest that the properties of muscle fibres that are likely to depend on myosin, such as velocity of shortening, can change without a change in myosin isoform. That a given myosin isoform can modify its properties without shifting to another isoform is confirmed by some analyses of isolated myosin in vitro. The present review is mainly focused on findings that challenge the role of myosin isoforms in determining the functional heterogeneity of skeletal muscle. The work also reports on potential mechanisms behind such changes in myosin function independent of a shift in myosin isoform: the coexistence of different myosin heavy chain (MHC) isoforms in the same fibre, the existence of as yet undetected MHC isoforms, myosin light chain isoforms, post-translational modifications of myosin, the role of other myofibrillar proteins, geometry of the sarcomere and the myosin concentration in single fibres.     

Myosin Isoform Fiber Type and Fiber Size in the Tail of the Virginia Opossum (Didelphis virginiana)

Muscle fiber type is a well studied property in limb muscles, however, much less is understood about myosin heavy chain (MHC) isoform expression in caudal muscles of mammalian tails. Didelphid marsupials are an interesting lineage in this context as all species have prehensile tails, but show a range of tail‐function depending on either their arboreal or terrestrial locomotor habits. Differences in prehensility suggest that MHC isoform fiber types may also be different, in that terrestrial opossums may have a large distribution of oxidative fibers for object carrying tasks instead of faster, glycolytic fiber types expected in mammals with long tails. To test this hypothesis, MHC isoform fiber type and their regional distribution (proximal/transitional/distal) were determined in the tail of the Virginia opossum (Didelphis virginiana). Fiber types were determined by a combination of myosin‐ATPase histochemistry, immunohistochemistry, and SDS‐PAGE. Results indicate a predominance of the fast MHC‐2A and ‐2X isoforms in each region of the tail. The presence of two fast isoforms, in addition to the slow MHC‐1 isoform, was confirmed by SDS‐PAGE analysis. The overall MHC isoform fiber type distribution for the tail was: 25% MHC‐1, 71% MHC‐2A/X hybrid, and 4% MHC‐1/2A hybrid. Oxidative MHC‐2A/X isoform fibers were found to be relatively large in cross‐section compared to slow, oxidative MHC‐1 and MHC‐1/2A hybrid fibers. A large percentage of fast MHC‐2A/X hybrids fibers may be suggestive of an evolutionary transition in MHC isoform distribution (fast‐to‐slow fiber type) in the tail musculature of an opossum with primarily a terrestrial locomotor habit and adaptive tail‐function. Anat Rec, 2013. © 2012 Wiley Periodicals, Inc.     

Limb myosin heavy chain isoproteins and muscle fiber types in the adult goat (Capra hircus)

The primary focus of this study was the accurate classification of limb skeletal muscle fiber types in adult goats (Capra hircus) according to the myosin heavy chain (MHC) isoform they express. Combined methodologies of gel electrophoresis, immunoblotting, immunohistochemistry, myofibrillar ATPase (mATPase), and quantitative metabolic enzyme histochemistry of M. semitendinosus samples were developed. Three MHCs were identified and tentatively designated as types I, IIA, and IIX. Five fiber types were defined immunohistochemically according to their MHC content: I, I+IIA, IIA, IIAX, and IIX. The hybrid fast-twitch fibers (IIAX) totaled 21% of the fiber population analyzed. The three major pure fibers (I, IIA, and IIX) could be objectively separated upon the basis of their mATPase activities after acid and alkaline preincubations. The prominent number of hybrid fibers, however, could not be delineated with these mATPase methods. Metabolic and size properties of muscle fibers varied according to their MHC content, but overlapped the full range of muscle fiber phenotypes. These integrated data demonstrate that type II skeletal muscle fibers of small ruminants have been misclassified in previous studies. The immunohistochemical approach developed in the present study offers new prospects for muscle fiber typing in caprine experimental studies and meat production technologies.     

Myosin heavy chain isoform composition and stretch activation kinetics in single fibres of Xenopus laevis iliofibularis muscle

Skeletal muscle is composed of specialized fibre types that enable it to fulfil complex and variable functional needs. Muscle fibres of Xenopus laevis , a frog formerly classified as a toad, were the first to be typed based on a combination of physiological, morphological, histochemical and biochemical characteristics. Currently the most widely accepted criterion for muscle fibre typing is the myosin heavy chain (MHC) isoform composition because it is assumed that variations of this protein are the most important contributors to functional diversity. Yet this criterion has not been used for classification of Xenopus fibres due to the lack of an effective protocol for MHC isoform analysis. In the present study we aimed to resolve and visualize electrophoretically the MHC isoforms expressed in the iliofibularis muscle of Xenopus laevis, to define their functional identity and to classify the fibres based on their MHC isoform composition. Using a SDS-PAGE protocol that proved successful with mammalian muscle MHC isoforms, we were able to detect five MHC isoforms in Xenopus iliofibularis muscle. The kinetics of stretch-induced force transients (stretch activation) produced by a fibre was strongly correlated with its MHC isoform content indicating that the five MHC isoforms confer different kinetics characteristics. Hybrid fibre types containing two MHC isoforms exhibited stretch activation kinetics parameters that were intermediate between those of the corresponding pure fibre types. These results clearly show that the MHC isoforms expressed in Xenopus muscle are functionally different thereby validating the idea that MHC isoform composition is the most reliable criterion for vertebrate skeletal muscle fibre type classification. Thus, our results lay the foundation for the unequivocal classification of the muscle fibres in the Xenopus iliofibularis muscle and for gaining further insights into skeletal muscle fibre diversity.