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.     

Calcium uptake and release modulated by counter-ion conductances in the sarcoplasmic reticulum of skeletal muscle

The sarcoplasmic reticulum (SR) plays the central role in regulating the free myoplasmic Ca²⁺ level for the contractile activation of skeletal muscle. The initial stages of the voltage-controlled Ca²⁺ release mechanism are known in molecular detail. However, there is still very little known about the later stages of Ca²⁺ uptake and total Ca²⁺ turnover in the contraction–relaxation cycle under normal physiological conditions or under conditions influenced by fatigue or disease. Ca²⁺ uptake and release are both accompanied by ‘counter-ion’ movements across the SR membrane which prevent or reduce the generation of SR membrane potentials and balance for electroneutrality in the SR lumen. The SR membrane is permeable for the cations K⁺, Na⁺, H⁺ and Mg²⁺ and the anion Cl^-. Using electron-probe X-ray microanalysis, it has been shown that during tetanic stimulation the Ca²⁺ release was mainly balanced by uptake of K⁺ and Mg²⁺, leaving a charge deficit that was assumed to be neutralized via H⁺ ion or organic counter-ion movement. The low time resolution of electron-probe X-ray microanalysis leaves the possibility of other transient concentration changes in the SR, e.g. for Cl^- ions. Possible physiological roles of the SR counter-ion conductances can be tested using skinned muscle fibre preparations with intact sarcoplasmic reticulum and removed or chemically permeabilized outer sarcolemma. In skinned fibres, the SR K⁺ conductance can be effectively reduced with SR K⁺ channel blockers such as 4-aminopyridine, tetraethylammonium and decamethonium. Interestingly, these blockers increase Ca²⁺ loading as well as Ca²⁺ release, whereas other less specific blockers, such as 1.10-bis-quanidino-n-decane, seem to reduce Ca²⁺ release, possibly also via blocking Ca²⁺ release channels. Thus, it seems very important also to test the effects of counter-currents carried by K⁺, Mg²⁺, H⁺ or Cl^- ions on intact and voltage-clamped single-fibre preparations.     

Effects of Deafferentation on the Size and Myosin Phenotype of Muscle Fibers on Stretching of the Rat Soleus Muscle in Conditions of Gravitational Unloading

The aim of the present work was to assess the contributions of the reflex and local components to preventing decreases in the size and changes in the ratio of fibers containing the slow and fast isoforms of myosin heavy chains during chronic stretching of a postural muscle in rats in conditions of gravitational unloading. A unilateral surgical deafferentation method was used. The results demonstrated that deafferentation of the hindlimb had no effect on preventing reductions in muscle fiber size in conditions of chronic muscle stretching in conditions of gravitational unloading. The results obtained from these experiments did not support the hypothesis that the predominant contribution to preventing the development of atrophic changes comes from activation of muscle afferents in chronic stretching of the unloaded muscle. Deafferentation of both suspended animals and those with normal motor activity led to increases in the proportion of soleus muscle fibers containing the slow isoforms of myosin heavy chain.     

Effects of fatigue on depolarization‐ and caffeine‐induced contractures of skinned fibres

Aims: Fatigue has been shown to cause intrinsic alterations in sarcoplasmic reticulum (SR) Ca²⁺ release. Methods: In this investigation, frog semitendinosus muscles were stimulated to fatigue, in vitro (80 Hz, 100 ms, 1 train s^?1, 5 min). Immediately after stimulation, single fibres were removed and skinned using either chemically or mechanically skinning. Contralateral muscle were treated similarly but were not stimulated. Results: In fatigued, saponin skinned fibres, contracture responses to low [caffeine] (4–8 mm ) were depressed compared with control. However, responses to high concentrations (10–15 mm ) were not different between conditions. In the fatigued, mechanically skinned fibres, responses to chloride depolarization were depressed at all [chloride] (20–100 mm ) compared with control. Conclusions: These results suggest that fatigue causes intrinsic alterations in both the SR Ca²⁺ release channel as well as communication between the transverse‐tubule and the SR.     

Effects of age on sarcoplasmic reticulum properties and histochemical composition of fa stand slow-twitch rat muscles

Calcium release activity of sarcoplasmic reticulum and enzyme-histochemical properties were investigated in extensor digitorum longus (e.d.l.) and soleus muscles in young (4 months) and old (24 months) male rats. With age, the caffeine threshold concentration for calcium release from the sarcoplasmic reticulum of soleus skinned muscle fibres showed only minor modifications. On the other hand, in e.d.l. skinned muscle fibres, the caffeine threshold concentration decreased significantly (P < 0.05). The histochemical fibre type composition changed with age both in soleus and in e.d.l. muscles, showing a common transformation toward a more oxidative histochemical profile. In fact, in aged soleus, a significant (P < 0.05) increase was observed of type 1 fibres to represent almost the totality of the muscle fibres (more than 98%), while types 2C and 2A were reduced in proportion. In aged e.d.l. the percentage of type 1 (P < 0.05), 2A and 2X (a recently identified fourth component of the fast-twitch muscle types) fibres increased, with a reduction of type 2B (P < 0.01) fibres. The present results suggest that the changes in contractile properties of aged muscles may be related to the changes not only in fibre composition but also in the mechanism of calcium release from sarcoplasmic reticulum.     

Structural Implications of β‐Cardiac Myosin Heavy Chain Mutations in Human Disease

Over 500 disease‐causing point mutations have been found in the human β‐cardiac myosin heavy chain, many quite recently with modern sequencing techniques. This review shows that clusters of these mutations occur at critical points in the sequence and investigates whether the many studies on these mutants reveal information about the function of this protein. Anat Rec, 297:1670–1680, 2014. © 2014 Wiley Periodicals, Inc.     

Design Principles of Reptilian Muscles: Calcium Cycling Strategies

The ultrastructure of the sarcoplasmic reticulum (SR) in skeletal muscles was compared among different reptile species (watersnake, boa constrictor, lizard, and turtle) and a mammal (mouse). Morphometric analysis demonstrates a pattern of increasing calsequestrin (CASQ) content in the lumen of SR from turtle to lizard, watersnake, and boa constrictor, and this content is in all cases higher than in mouse. In all reptiles sampled except turtle, CASQ is not confined to the junctional sarcoplasmic reticulum (jSR) cisternae as it is in other species. It instead fills the entire longitudinal (free) SR (fSR) regions, and in the extreme case of snakes, the shape of the SR is modified around the extra CASQ. We suggest that high CASQ content may represent an ATP‐saving adaptation that permits relatively low metabolic rates during prolonged periods of fasting and inactivity, particularly in watersnake and boa constrictor. Anat Rec, 299:352–360, 2016. © 2015 Wiley Periodicals, Inc.     

Myosins and deafness

The discovery in the past few years of a huge diversity within the myosin superfamily has been coupled with an understanding of the role of these motor proteins in various cellular functions. Extensive studies have revealed that myosin isoforms are not only involved in muscle contraction but also in crucial functions of many specialized mammalian cells such as melanocytes, kidney and intestinal brush border microvilli, nerve growth cones or inner ear hair cells. A search for genes involved in the pathology of human genetic deafness resulted in identification of three novel myosins: myosin VI, myosin VIIA and, very recently, myosin XV. The structure, tissue and cellular distribution of these myosin isoforms, as well as mutations detected within their genes that have been found to affect the hearing process, are described in this review.     

A Mutation in the CASQ1 Gene Causes a Vacuolar Myopathy with Accumulation of Sarcoplasmic Reticulum Protein Aggregates

A missense mutation in the calsequestrin‐1 gene (CASQ1) was found in a group of patients with a myopathy characterized by weakness, fatigue, and the presence of large vacuoles containing characteristic inclusions resulting from the aggregation of sarcoplasmic reticulum (SR) proteins. The mutation affects a conserved aspartic acid in position 244 (p.Asp244Gly) located in one of the high‐affinity Ca²⁺‐binding sites of CASQ1 and alters the kinetics of Ca²⁺ release in muscle fibers. Expression of the mutated CASQ1 protein in COS‐7 cells showed a markedly reduced ability in forming elongated polymers, whereas both in cultured myotubes and in in vivo mouse fibers induced the formation of electron‐dense SR vacuoles containing aggregates of the mutant CASQ1 protein that resemble those observed in muscle biopsies of patients. Altogether, these results support the view that a single missense mutation in the CASQ1 gene causes the formation of abnormal SR vacuoles containing aggregates of CASQ1, and other SR proteins, results in altered Ca²⁺ release in skeletal muscle fibers, and, hence, is responsible for the clinical phenotype observed in these patients.     

Mechanisms underlying changes of tetanic [Ca2+]i and force in skeletal muscle

Force development in skeletal muscle is driven by an increase in myoplasmic free [Ca²⁺] ([Ca²⁺]_i) due to Ca²⁺ release from the sarcoplasmic reticulum (SR). The magnitude of [Ca²⁺]_i elevation during stimulation depends on: (a) the rate of Ca²⁺ release from the SR, (b) the rate of Ca²⁺ uptake by the SR, and (c) the myoplasmic Ca²⁺ buffering. We have used fluorescent Ca²⁺ indicators to measure [Ca²⁺]_i in intact, single fibres from mouse and Xenopus muscles under conditions where one or more of the above factors are changed. The following interventions resulted in increased tetanic [Ca²⁺]_i: β-adrenergic stimulation, which potentiates the SR Ca²⁺ release; application of 2,5-di(tert-butyl)-1,4-benzohydroquinone, which inhibits SR Ca²⁺ pumps; application of caffeine, which facilitates SR Ca²⁺ release and inhibits SR Ca²⁺ uptake; early fatigue, where the rate of SR Ca²⁺ uptake is reduced; acidosis, which reduces both the myoplasmic Ca²⁺ buffering and the rate of SR Ca²⁺ uptake. Reduced tetanic [Ca²⁺]_i was observed in late fatigue, due to reduced SR Ca²⁺ release, and in alkalosis, due to increased myoplasmic Ca²⁺ buffering. Force is monotonically related to [Ca²⁺]_i, but depends also on the myofibrillar Ca²⁺ sensitivity and the maximum force cross-bridges can produce. This is clearly illustrated by changes of intracellular pH where, despite a lower tetanic [Ca²⁺]_i, tetanic force is higher in alkalosis than acidosis due to increases of myofibrillar Ca²⁺ sensitivity and maximum cross-bridge force.     

The expanded collagen VI family: new chains and new questions

Abstract

Collagen VI is a component of the extracellular matrix of almost all connective tissues, including cartilage, bone, tendon, muscles and cornea, where it forms abundant and structurally unique microfibrils organized into different suprastructural assemblies. The precise role of collagen VI is not clearly defined although it is most abundant in the interstitial matrix of tissues and often found in close association with basement membranes. Three genetically distinct collagen VI chains, α1(VI), α2(VI) and α3(VI), encoded by the COL6A1. COL6A2 and COL6A3 genes, were first described more than 20 years ago. Their molecular assembly and role in congenital muscular dystrophy has been broadly characterized. In 2008, three additional collagen VI genes arrayed in tandem at a single gene locus on chromosome 3q in humans, and chromosome 9 in mice, were described. Following the naming scheme for collagens the new genes were designated COL6A4. COL6A5 and COL6A6 encoding the α4(VI), α5(VI) and α6(VI) chains, respectively. This review will focus on the current state of knowledge of the three new chains.     

Muscle Biopsy: A Diagnostic Tool in Muscle Diseases

Abstract

Muscle biopsy is an important and essential tool in the diagnosis and treatment of muscle disease. For several decades, histological staining of paraffin-embedded tissue was used in muscle pathology. In the past few decades, fresh-frozen enzyme histochemical techniques have become the standard for assessing muscle disease. They have been complemented by the use of electron microscopy to characterize ultrastructural changes. More recently, the discovery of certain muscle proteins and the development of antibodies made possible the combination of enzyme histochemical and immunohistochemical methods to better assess muscle changes. In this review, we discuss the roles of histochemistry, enzyme histochemistry, immunohistochemistry, and electron microscopy in the diagnosis of skeletal muscle pathology (The J Histotechnol 31:101, 2008).

Submitted March 3, 2008; accepted with revisions May 24, 2008     

Expression of E-Selectin in Ischemic and Reperfused Human Skeletal Muscle

This work was undertaken to assess the role of endothelial E-selectin in the development of neutrophil accumulation into the ischemic and reperfused human skeletal muscle and eventually in the genesis of ischemia-reperfusion syndrome. Twelve patients affected by abdominal aortic aneurysm who were undergoing reconstructive vascular surgery were studied. Muscle biopsies from the right femoral quadriceps were taken (1) immediately after anesthesia, as control samples, (2) before declamping the aorta, as ischemic samples, and (3) 30 minutes after reperfusion and then processed for immunohis-tochemical and ultrastructural analysis. Immunohistochemistry revealed a strong positive reaction for E-selectin on the venular endothelium during ischemia and reperfusion. Ultrastructural investigation showed that reactivity for E-selectin matched neutrophil accumulation of the skeletal muscle tissue. This phenomenon was dependent upon a complex series of events that included neutrophil adhesion to the inner surface of the postcapillary venules, passage through endothelial intercellular junctions, and migration distally into the interstitial spaces of the skeletal muscle tissue. Neutrophil tissue infiltration was also associated with ultrastructural signs of tissue damage at reperfusion. This is in agreement with accumulating evidence indicating a role for tissue infiltrating neutrophils in the genesis of toxic O₂ free radicals. Our data suggest that E-selectin expression on the vascular endothelium of human skeletal muscle May-June represent a key regulatory point in the process of neutrophil tissue accumulation and indicate an active role for the venular endothelium in the development of human ischemia-reperfusion syndrome.     

Effect of cyclopiazonic acid,an inhibitor of the sarcoplasmic reticulum Ca‐ATPase,on skeletal muscles from normal and mdx mice

Aim: In this study, we investigated Ca²⁺ loading by the sarcoplasmic reticulum in skeletal muscle from mdx mice, an animal model of human Duchenne's muscular dystrophy, at two stages of development: 4 and 11 weeks. Method: Experiments were conducted on fast‐ (extensor digitorum longus, EDL) and slow‐ (soleus) twitch muscles expressing different isoforms of Ca²⁺‐ATPase, which is responsible for the uptake of Ca²⁺ by the sarcoplasmic reticulum. Results: In sarcoplasmic reticulum vesicles, the ATP‐dependent activity and sensitivity to cyclopiazonic acid (CPA), an inhibitor of the sarcoplasmic reticulum Ca²⁺‐ATPase, were similar in mdx and normal EDL muscle. Furthermore, in chemically‐skinned fibres from both normal and mdx muscles, the presence of CPA induced a decrease in Ca²⁺ uptake by the sarcoplasmic reticulum. However, the sensitivity to CPA was lower in mdx EDL muscle than in normal muscle. In addition, in EDL muscle from 4‐week‐old mdx mice, the expression of the slow Ca²⁺‐pump isoform (SERCA2a) was significantly increased, without any accompanying change in slow myosin expression. In contrast, the expression and function of the Ca²⁺‐ATPase in mdx soleus muscles at 4‐ and 11‐weeks of development did not differ from those in age‐matched controls. Conclusion: These findings show that in dystrophic muscle, where the Ca²⁺ homeostasis was perturbed, the Ca²⁺ handling by the sarcoplasmic reticulum was altered in fast‐twitch muscle, and this was associated with the expression of the slow isoform of SERCA. In these muscles, reduced Ca²⁺ uptake could then contribute to an elevated concentration of Ca²⁺ in the cytosol, and also to Ca²⁺ depletion of the sarcoplasmic reticulum.     

Myosin phosphatase: subunits and interactions

Myosin phosphorylation is an important mechanism in regulating contractile activity of smooth muscle. The level of myosin phosphorylation depends on the balance of two enzymes, myosin light chain kinase and myosin phosphatase. Recently it has been discovered that myosin phosphatase can be regulated and this renewed interest in characterization of the phosphatase. It is suggested that the myosin phosphatase is composed of three subunits: a catalytic subunit of type 1 phosphatase (δ isoform; PP1cδ); and two non-catalytic subunits, large and small (M20). The large subunit is thought to be a targeting subunit and is termed myosin phosphatase target subunit (MYPT). There are several isoforms of MYPT and two genes have been identified on human chromosomes 1 and 12. A dominant feature of MYPT is a series of ankyrin repeats at the N-terminal end of the molecule and these may be involved in binding to the catalytic subunit and to substrate, phosphorylated myosin. In addition, at the N-terminal fringe of the ankyrin motifs is a consensus PP1c binding motif. The function of the M20 subunit is not established but is known to bind to the C-terminal end of MYPT. Various interactions between subunits that might be relevant for the regulation of phosphatase activity are discussed.     

Human Masseter Muscle Fibers From the Elderly Express Less Neonatal Myosin Than Those of Young Adults

In contrast to limb muscles where neonatal myosin (MyHC‐neo) is present only shortly after birth, adult masseter muscles contain a substantial portion of MyHC‐neo, which is coexpressed with mature MyHC isoforms. Changes in the numerical and area proportion of muscle fibers containing MyHC‐neo in masseter muscle with aging could be expected, based on previously reported findings that (i) developmental MyHC‐containing muscle fibers exhibit lower shortening velocities compared to fibers with exclusively fast MyHC isoforms and (ii) transformation toward faster phenotype occurs in elderly compared to young masseter muscle. In this study, we detected MyHC isoforms in the anterior superficial part of the human masseter muscle in a sufficiently large sample of young, middle‐aged, and elderly subjects to reveal age‐related changes in the coexpression of MyHC‐neo with adult MyHC isoforms. MyHC isoforms were visualized with immunoperoxidase method and the results were presented by (i) the area proportion of fibers containing particular MyHC isoforms and (ii) the numerical proportion of fiber types defined by MyHC‐1, ‐2a, ‐2x, and ‐neonatal isoform expression from a successive transverse sections. We found a lower numerical and area proportion of fibers expressing MyHC‐neo as well as a lower area proportion of fibers containing MyHC‐1 in elderly than in young subjects. We conclude that the diminished expression of MyHC‐neo with age could point to a lower regeneration capacity of masseter muscle in the elderly. Anat Rec, 2012. © 2012 Wiley Periodicals, Inc.     

The role of phospholamban and SERCA3 in regulation of smooth muscle-endothelial cell signalling mechanisms: evidence from gene-ablated mice

It is generally agreed that intracellular Ca²⁺ stores, the sarco(endo)plasmic-reticulum (SER), affect Ca²⁺ homeostasis and thus contractility of vascular smooth muscle. There is, however, no general consensus as to the magnitude of the SER contribution to Ca²⁺ handling, the basis for isoforms of the SER Ca²⁺-ATPases (SERCAs) or the role of an SER-associated regulatory protein, phospholamban (PLB). Although the biochemical and cell biological roles of the SER have been intensely studied in vitro, the development of gene-targeted and transgenic mouse models enables one to extend our information to the in vivo levels. A brief review of the role of PLB and SERCA function in vascular and endothelial cell function is presented. Studies on the PLB gene-ablated mouse indicate that vascular contractility is considerably altered. This is mirrored by changes in intracellular Ca²⁺. Moreover, differences in contractility of the gene-ablated tissues are eliminated by treatment with cyclopiazonic acid, which pharmacologically abolishes SER function by inhibiting the Ca²⁺-ATPase. Thus PLB modulation of sarcoplasmic reticulum (SR) Ca²⁺ uptake plays a major role in modulating vascular contractility. It is interesting that endothelium-dependent relaxation was decreased in the PLB-deficient aorta. This is surprising in light of the PLB distribution, thought to be limited to cardiac, slow skeletal and smooth muscle. Our data indicate the presence of PLB in endothelial cells and point to an unrecognized pathway for modulation of endothelial cell [Ca²⁺]_i and vascular contractility. Data from smooth muscle tissues of the SERCA3 gene-ablated mouse demonstrate that this isoform affects endothelium-dependent function, but not that of smooth muscle, consistent with its known distribution. This isoform appears to perform a modulatory function, rather than the more essential role of SERCA2. Gene-targeted and transgenic models provide an important avenue for understanding the role of SER in vascular signalling.     

Calcium transport and ATPase activity in mitochondria and fragments of sarcoplasmic reticulum of the heart and muscles of rabbits with hypercholesteremia

Keeping rabbits on a high-cholesterol diet (1 g/kg) for 3–7 months led to an increase in cholesterol concentration in the mitochondrial membranes and fragments of the sarcoplasmic reticulum (SPR) of the myocardium and skeletal muscles. Saturation of the membranes with cholesterol led to a decrease in efficiency of the Ca-pump of the SPR, as reflected in lowering of the Ca/ATP ratio and an increase in the outflow of Ca⁺⁺ from the SPR. Under these conditions the rate of accumulation of Ca⁺⁺ was higher in SPR than in the mitochondria. Activity of mitochondrial Mg⁺⁺-activated 2,4-DNP-ATPase was reduced in hypercholesteremia.Laboratory of Molecular Pathology and Biochemistry, Institute of General Pathology and Pathological Physiology, Academy of Medical Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR A. M. Chernukh.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 89, No. 3, pp. 292–294, March, 1980.     

核转录因子反义核酸对慢性心力衰竭大鼠模型心肌肌凝蛋白同功酶和细胞因子的影响

目的:探讨核转录因子(nuclear factor kappa B, NF-κB)反义核酸(antisense oligonucleotide, AS-ON)对慢性心力衰竭(chronic heart failure, CHF) 病程心肌肌凝蛋白同功酶(myosin isoenzyme, MI)和细胞因子肿瘤坏死因子α(tumor necrosis factor α, TNF-α)、白细胞介素-1β(interleukin-1β, IL-1β)和Fas的影响.方法:采用纯种Wister大鼠作为实验动物,分为正常对照组、模型组和NF-κB AS-ON治疗组,每个亚组均10只.采用腹主动脉结扎方法制作慢性心力衰竭模型,治疗组在手术结扎后给予心包注射NF-κB反义核酸治疗.术后每两周行超声心动图、血液动力学检测,并取静脉血放射免疫分析检测TNF-α和IL-1β,酶联免疫吸附实验(enzyme linked immunosorbant assay,ELISA)检测Fas水平,提取心肌肌凝蛋白重链(cardiac myosin heavy chain, CMHC),非变性聚丙烯酰胺凝胶电泳(SDS-PAGE)检查心肌肌凝蛋白同功酶谱(myosin isoenzyme, MI).结果:腹主动脉结扎后3月内是心功能代偿期,6月时是心功能失代偿期.NF-κB AS-ON治疗心力衰竭改善心功能,降低TNF-α、IL-1β和Fas水平,减轻MI V1水平向V3迁移.结论:NF-κB AS-ON治疗慢性心力衰竭疗效显著,其生化机理可能是维护细胞网络正常构成以及抑制心MI由V1优势向V3迁移.     

实验大鼠斜方肌肌纤维型组成及分布研究

目的探讨大鼠斜方肌的肌纤维型组成和分布,借以了解该肌功能。方法取成年SD大鼠斜方肌升部肌组织进行冰冻切片(8μm厚),采用Guth-Samaha肌球蛋白ATP酶组织化学染色法并稍做改良,对其进行肌纤维分型研究。结果SD大鼠斜方肌经肌球蛋白ATP酶组织化学染色后可明确分出2种肌纤维型,即白色的Ⅰ型纤维(慢缩纤维)和深褐色的Ⅱ型纤维(快缩纤维),2种肌纤维在肌内呈棋盘样均匀分布;图像分析计数其Ⅰ型纤维占(48.8±6.9)%,Ⅱ型纤维比例为(51.2±6.9)%,2者比较差异无统计学意义(P>0.05)。结论SD大鼠斜方肌2型肌纤维所占比例均等,与其维持颈背部姿势的作用一致。