Five myofibrillar lesion types in eccentrically challenged,unloaded rat adductor longus muscle—a test model

Sarcomere disruptions are observed in the adductor longus (AL) muscles following voluntary reloading of spaceflown and hindlimb suspension unloaded (HSU) rat, which resemble lesions in eccentrically challenged muscle. We devised and tested an eccentric contraction (ECCON) test system for the 14‐day HSU rat AL. Six to 7 hours following ECCON, ALs were fixed to allow immunostaining and electron microscopy (EM). Toluidine blue‐stained histology semithin sections were screened for lesion density (#/mm²). Serial semithin sections from the ECCON group were characterized for myosin immunointensity of lesions. Five myofibrillar lesion types were identified in histological semithin sections: focal contractions; wide A‐bands; opaque areas; missing A‐bands; and hyperstretched sarcomeres. Lesion density by type was greater for ECCON than NonECCON ALs (P ≤ 0.05; focal contractions and opaque regions). Lesion density (#‐of‐all‐five‐types/mm²) was significantly different (ECCON: 23.91 ± 10.58 vs. NonECCON: 5.48 ± 1.28, P ≤ 0.05; ECCON vs. SHAM: 0.00 ± 0.00; P ≤ 0.025). PostECCON optimal tension decreased (Poi‐drop, 17.84 ± 4.22%) and was correlated to lesion density (R² = 0.596), but prestretch tension demonstrated the highest correlation with lesion density (R² = 0.994). In lesions, the darkly staining A‐band lost the normally organized thick filament alignment to differing degrees across the different lesion types. Ranking the five lesion types by a measure of lesion length deformation (hypercontracted to hyperstretched) at the light microscopy level, related to the severity of thick filament registry loss across the lesion types at the electron microscopic level. This ranking suggested that the five lesion types seen in semithin sections at the light level represented a lesion progression sequence and paralleled myosin immunostaining loss as the distorted A‐band filaments spread across the hyperlengthening lesion types. Lesion ultrastructure indicated damage involved calcium homeostasis loss (focal contraction lesions) and “thick‐filamentcentering” failure of titin (wide A‐band lesions) in the early stages of lesion development. Anat Rec 254:39–52, 1999. © 1999 Wiley‐Liss, Inc.     

A new twist in cardiac muscle: dislocated and helicoid arrangements of myofibrillar z-disks in mammalian ventricular myocytes

Using deconvolved confocal microscopy of fluorescently labeled markers for z-disks, t-tubules and ryanodine receptors, we have examined sarcomere organization in cardiac myocytes from rat, rabbit and human. We show that sarcomeres exhibit dislocations in registration and occasionally more complex helicoidal topology. This organization was present at both slack (∼ 1.8 μm) and long sarcomere lengths (∼ 2.2 μm). Misregistrations in z-disks persisted over 15-20 sarcomere lengths and appeared to arise primarily from variations in fiber direction; particularly as myofibrils pass around nuclei. In addition, myofibrils twist along the cell length. T-tubules generally follow the sarcomere z-disks although additional elements bridging adjacent myofibrils and along the length of the myofibril are present to varying degrees in all cells. Ryanodine receptors (the sarcoplasmic reticulum Ca²⁺ release channel) are generally located within 250 nm of the local plane containing t-tubules and z-disks, but a small fraction (∼ 2%) is found on longitudinal elements of the t-system between z-disks. The results are discussed with respect to the possible role(s) of such complex z-disk organization and z-disk dislocations in the maintenance of cell structure and sarcomere assembly. In addition, the non-planar organization of z-disks may be important in the propagation of local Ca²⁺ waves which may have a useful role in helping maintain the uniformity of sarcomere activation in the presence of t-tubule remodeling.     

肌纤维瘤30例临床病理分析

目的:探讨肌纤维瘤的临床病理特征、诊断及鉴别诊断。方法:回顾性分析2012至2019年就诊于安徽省儿童医院的30例经手术切除诊断为肌纤维瘤的患者的临床病理特征、治疗和预后。结果:30例患者;男16例,女14例,年龄42 h^10岁,中位年龄为15.5个月。均为单发孤立性包块。出生时即发现包块的9例,发生于头颈部10例,四肢8例,躯干11例,1例发生于末端回肠肠壁内。18例肿物位于真皮及皮下浅层,8例位于深部肌肉内,3例侵犯额骨,1例位于肠壁内。镜检显示梭形肿瘤细胞呈现典型的带状,其特征是周围细长细胞排列成短束或漩涡状,中心圆形至多边形细胞围绕薄壁不规则分支血管形成血管外周细胞瘤样结构。细胞无明显异型性,核分裂象罕见。免疫表型:肿瘤细胞表达Viment i n和SMA,不表达S-100,Desmin,CD34,CK,CD99,CD117,β-catenin,ALK,STAT6和GRIA2,Ki-67分析显示低增值率(<5%)。所有患者经外科手术完整切除瘤体。术后随访1~798个月,除3例失访,其余患者均存活,且无复发。结论:肌纤维瘤是婴幼儿少见肿瘤,预后良好。综合临床、组织病理学和免疫组织化学标志对于正确诊断是必须的。     

Cardiac myofibrillar ATPase activity in diabetic rats

Diabetes was induced by an intravenous injection of 65 mg/kg streptozotocin and hearts were removed 8 weeks later for the isolation of myofibrils. The basal ATPase activity of myofibrils from diabetic hearts was significantly lower than the controls. Although Ca²⁺-stimulated ATPase activity was also depressed in diabetic myocardium, the dependency of diabetic myofibrils on free calcium concentration was not different from that of control. The basal and Ca²⁺-stimulated ATPase activities in diabetic rats demonstrated a greater sensitivity to KCl than control preparations. The myofibrillar basal ATPase, unlike Ca²⁺-stimulated ATPase, in diabetic animals exhibited a greater sensitivity to ethylene glycol. These results support the view regarding the presence of some subtle structural and conformational changes in diabetic myofibrils.     

Myofibrillar AlPase, DNA and Hydroxyproline Content of Human Hypertrophied Heart

70 human hearts were studied less than 36 hours after death. The apex, and in some cases other parts of the myocardium were homogenized, DNA, hydroxyproline content, myofibrillar Ca2+ and Mg2+ ATPase were measured. In normal hearts the DNA and collagen content were 372 +/- 9 mg and 36 +/- 7 mg. Ca2+ and Mg2+ ATPase of the myofibrils prepared from these hearts have shown the same specific activity (35 +/- 5 and 34 +/- 6 nmol/min./mg) as those from fresh biopsies taken during open-chest surgery. The heart weight correlates with the DNA content (r= + 0.58 -p less than 0.01) and with the myofibrillar ATPase (r= - 0.33 - p less than 0.02) but not with the DNA concentration nor with the collagen content or concentration. The main result of this study was the presence of a negative correlation between the DNA content of the heart and the Mg2+ or Ca2+ myofibrillar ATPase (r= - 0.31, p less than 0.05 - r= - 0.45, p less than 0.01). This correlation was analysed with reference to the histological and biochemical studies published by several authors in human or experimental heart hypertrophy and it was suggested that in human heart hypertrophy the decrease of the myofibrillar or myosin ATPase is a direct consequence of the high degree of polyploidy of the muscular cells observed in this condition.     

Subcellular and Molecular Mechanisms of the Effects of Cardiac Glycosides and Angiotensin-Converting Enzyme Inhibitors on Contractile Function and Energy Conversion in Myocardial Myofibrils under Normal Conditions and during Acute Cardiac Insufficiency

Experiments on skinned and hybrid myocardial fibers isolated from normal dogs and animals subjected to 120-min occlusion of the anterior interventricular branch of the coronary artery showed that in contrast to cardiac glycosides, angiotensin-converting enzyme inhibitors suppress contractile ability of myocardial myofibrils in a dose-independent manner within the concentration range of 10_-12-10_-4 M. This effect is accompanied by a decrease in fiber relaxation rate most pronounced in the presence of captopril. Actin, the major protein of fine filaments is the target for beta-acetyldigoxin, K-strophanthin, captopril, enalapril, and trandolapril in myocardial myofibrils. During coronary occlusion, the inhibitors of angiotensin-converting enzyme induce structural and conformational changes in actin that decrease efficiency of contraction. The data obtained cast doubt on advisability of therapeutic use of angiotensin-converting enzyme inhibitors in the therapy of myocardial infarction, especially in its early period.     

Myod1和Myog真核共表达载体构建及鉴定

背景：目前研究发现,生肌调节因子家族的各成员之间具有相互协同和相互促进的作用。因此,联合应用Myod1和Myog两个成员进行基因治疗,可能会取得更好的疗效,能够为防治失神经支配骨骼肌萎缩寻找新的思路。 目的：构建Myod1和Myog基因的真核共表达载体。 方法：通过RT-PCR的方法克隆大鼠Myod1和Myog基因的全长cDNA,酶切后依次插入到pVAX1载体中,以构建重组的Myod1和Myog真核共表达载体pVAX1-Myod1-IRES2-Myog-IRES2-EGFP,采用基因测序的方法进行鉴定。将pVAX1-Myod1-IRES2-Myog-IRES2-EGFP对体外培养的3T3细胞进行转染,利用Western blot检测3T3细胞中Myod1蛋白和Myog蛋白的表达,验证其能否正确表达目的蛋白。 结果与结论：基因测序结果表明,真核共表达载体pVAX1-Myod1-IRES2-Myog-IRES2-EGFP内的Myod1和Myog cDNA的序列长度及碱基顺序均与所公布的序列相同。将该载体转染到体外培养的3T3细胞内,Western blot能够检测到3T3细胞中Myod1和Myog蛋白的条带。结果证实,实验成功构建了重组Myod1和Myog真核共表达载体pVAX1-Myod1-IRES2-Myog-IRES2-EGFP。