Structure Of Muscle Fibers Research Articles

Гістологічні особливості литкового м’яза щура за умов хронічної алкоголізації та ішемії різної тривалості

Мета роботи – провести аналіз гістологічних змін у литковому м’язі за умов експериментальної ішемії різної тривалості, ускладненої хронічною алкоголізацією. Експеримент реалізовано на щурах інбредної лінії Wistar масою 140–160 г. Виділено такі групи тварин: контрольна, тварини з ішемією (1, 2 та 3 год), алкоголізовані тварини й алкоголізовані тварини з експериментально-індукованою ішемією тривалістю 1, 2, 3 год. Експериментальну ішемію здійснювали через 30 днів після введення останньої дози етилового спирту методом Халілова-Захірходжаєва через перетискування джгутом основних артерій. Гістологічну обробку тканини проводили за загальноприйнятою методикою, фарбувалили за методом Ван-Гізон. Виявлено, що за умов хронічної алкоголізації й ішемії різної тривалості порушуються структура й хід частково атрофованих унаслідок алкогольної міопатії волокон, відбуваються дегенеративні зміни в цілісності сарколеми, у деякої частини волокон зменшується об’єм міофібрил, ендомізій набрякає та починає некротизуватися, міофібрили роз’єднуються. Відзначено появу нейтрофілів поміж міофібрил і дифузні крововиливи, але, попри це, в окремих ділянках зберігається типова поперечна посмугованість. Отримані результати свідчать про негативну синергію міотоксичних впливів етилового спирту та руйнівного впливу судинної ішемії на волокна литкового м’яза щурів.

The effects of high pressure on the myofibrillar structure and meat quality of marinating Tan mutton

AbstractLamb leg meat (LLM) was marinated using solution of sodium chloride (NaCl) concentrations (0.04 g/g) for 15 min under high pressure (HP) treatment (100–400 MPa, 25°C) to investigate meat characteristics, volatile components and microstructure. HP treatment increased process yields during marinating, especially at 200 MPa, the shearing force and hardness reached their minimum value, which indicated that HP treatment (200 MPa) can effectively improve the tenderness of LLM. The electron microscopy revealed that HP modified the myofibrillar structure in the leg muscles. With the rise of pressure, the lightness (L*) value increased significantly. The red/green hue (a*) reached the maximum value at 200 MPa. HP influenced the formation of some key volatile compounds in LLM. LLM pressurized at 200–400 MPa had lower levels of furfural than control group, LLM pressurized at 200 MPa had higher levels of N‐nonanal and N‐octanal, lower levels of palmitic acid, but oleic acid and stearic acid was not detected. Only at 200–400 MPa, 2,3‐octanedione and 2‐octanone were detected in HP‐treated LLM.Practical applicationsHigh‐pressure (HP) is an effective technology as a pretreatment to postslaughter meat. Advantages include opportunities to improve tenderness and other characteristics of processed meat products by appropriate use of this technique. This study showed that application of high‐pressure premarinated treatment (200 MPa, 15 min, 25°C and 0.04 g/g salt content) could effectively improve the muscle fiber structure of lamb leg, several major volatile substances and tenderness. This work verifies the potential of HP for improving LLM characteristics and volatile components. These results can be beneficial for the applications of pressurized mutton in the mutton industry.

MRI ASSESSMENT OF MUSCULAR LESIONS IN LOWER LIMB

Background: Muscle disease is a disorder caused by derangement of the structure or function of muscle fiber, blood supplyand/or connective tissue element of the muscle ,the combination of clinical examination and MRI could improve the accuracy of phenotypic characterization of patients with muscular lesions, This may also be very helpful in the assessment of the degree of muscle compromise not only in the early phases of the disease but also during the follow-up and can be used especially in therapeutic trials. Aim of the work: To assess the role of MRI in detection and evaluation of muscle diseases and its prognostic value for the follow up. Patients and Methods: This study was conducted at the radiology department Ain Shams university, it included thirty patients, they all had clinical diagnosis have of muscular diseases of the lower limb, fulfilled inclusion criteria. Results: The sensitivity of MRI in detection of malignant lesions compared to histo-pathology and clinical diagnosis as gold standered was 83.3%, specificity was 91.7% and accuracy was 90%,76.7% of the studied cases had a benign which was lesion most frequently a hemangioma (10%), also 23.3% of the patients had a malignant lesion which was most frequently metastasis from other tumors (13.3%). Conclusion: MRI is the modality of choice in evaluating lower limb muscular lesions due to its high soft tissue contrast resolution, and multi-planar capabilities. MRI may allow clinicians to more accurately estimate the time required before patient can return tonormal life as well as the risk of recurrent injury.

Ways to reduce adverse effects of stress in pigs using nutritional factors

Modern intensive technologies for handling and growing highly productive animals are accompanied by significant changes in their homeostasis causing stress and adversely affecting their health and the quality of the products obtained from them. Depending on the cause, stress is classified as social (technological), environmental, dietary, and immunological. Various types of stress adversely affect the body and contribute to endocrine, energy balance, and carbohydrate-lipid metabolism disturbances, which adversely affects the animal resistance to diseases, productivity and reproductive characteristics. Stress leads to metabolic disorders and changes in the ratio of muscle and fatty tissues. Every year, the manifestations of antemortem and postmortem pathological changes in the microstructure of animal muscle tissue are increasingly noted. Moreover, the affected structures of muscle fibers are characterized by hyper contraction, disruption of cell membranes, and formation of extracellular protein substance represented by denatured forms of proteins reducing the nutritional value and consumer characteristics of the final product. The use of antioxidants in pig diets, including natural ones, helps to reduce the impact of environmental stress factors on animals and increase their adaptive capacity. This review focuses on the ways to reduce stress and the effect of flavonoids, including quercetin, whose properties have been extensively studied in recent years, in order to increase the resistance of highly productive animals to various stress factors.

Muscle fiber structure in an aging long-lived seabird, the black-legged kittiwake (Rissa tridactyla).

Many long-lived animals do not appear to show classic signs of aging, perhaps because they show negligible senescence until dying from "catastrophic" mortality. Muscle senescence is seldom examined in wild animals, yet decline in muscle function is one of the first signs of aging in many lab animals and humans. Seabirds are an excellent study system for physiological implications of aging because they are long-lived animals that actively forage and reproduce in the wild. Here, we examined linkages between pectoralis muscle fiber structure and age in black-legged kittiwakes (Rissa tridactyla). Pectoralis muscle is the largest organ complex in birds, and responsible for flight and shivering. We obtained and fixed biopsies from wild black-legged kittiwakes of known age. We then measured muscle fiber diameter, myonuclear domain and capillaries per fiber area among birds of differing ages. All muscle parameters were independent of age. Number of nuclei per mm of fiber showed a positive correlation with muscle fiber cross-sectional area, and myonuclear domain increased with muscle fiber diameter. Thus, as muscle fibers increased in size, they may not have recruited satellite cells, increasing the protein turnover load per nuclei. We conclude that senescence in a long-lived bird with an active lifestyle, does not entail mammalian-like changes in muscle structure.

The effects of ultrasonic treatment on the freezing rate, physicochemical quality, and microstructure of the back muscle of grass carp (Ctenopharyngodon idella)

The application and research of power ultrasound (PU) have rarely been reported in aquatic products processing. This study evaluates the effects of PU on the freezing rate, physicochemical properties, and microstructure of the back muscle of grass carp (Ctenopharyngodon idella) at various power densities and time intervals during both marination and immersion freezing (IF). The results show that the application of PU at 0.38 W/cm2 and above during IF can significantly shorten the length of precooling stage, phase transition and, total freezing time (P < 0.05), protect muscle fiber structure, resulting in decreased thawing loss, but it exhibited no significant effect on the protein carbonyl content, total sulfhydryl content and disulfide bond content. Ultrasonic marination (UM) with a maximum power density of 0.60 W/cm2 slightly increases the protein carbonyl content and decreases the total thiols without significant effect (P > 0.05). However, the disulfide bond content increases significantly (P < 0.05) after UM at 0.48 W/cm2 and above. PU treatment at 0.38 W/cm2 and above during marination and 0.48 W/cm2 and above during IF significantly promotes lipid oxidation. UM at 0.60 W/cm2 for up to 90 min and above results in visible damage to the muscle fiber membrane of grass carp (Ctenopharyngodon idella).

Qishen Yiqi Dropping Pills Ameliorates Doxorubicin-induced Cardiotoxicity in Mice via Enhancement of Cardiac Angiogenesis.

BackgroundQishen Yiqi Dropping Pills (QYDP) is a Chinese traditional medicine that has been applied to treat coronary heart disease and ischemic heart failure in China. However, few studies have explored whether QYDP exerted an effect on doxorubicin (Doxo)-induced cardiotoxicity. Hence, in this study we investigated the effect of QYDP on cardiotoxicity induced by doxorubicin (Doxo) and its potential mechanism.Material/MethodsMale C57BL/6 mice (20–25 g, 8–10 weeks old) were randomly assigned to 4 groups: Control group, QYDP group, Doxo group, and QYDP+Doxo group. The mice were intraperitoneal injected with Doxo weekly for 4 weeks to mimic the chronic toxicity. Four weeks after Doxo injection, echocardiography was applied to evaluate the left ventricular (LV) function, and the structure of the cardiac muscle fibers was analyzed with anti-actinin-2 antibody staining by immunofluorescence. Moreover, TUNEL staining and western blot analysis of Bax protein, Bcl-2 protein, and cleaved caspase-3 protein expression levels were conducted to explore whether QYDP exerted effect on cardiac apoptosis. In addition, Masson trichrome staining and western blot analysis of α-SMA protein expression levels were used to evaluate whether QYDP exerted an effect on cardiac fibrosis. Western blots and quantitative real-time polymerase chain reaction were applied to detect the vascular endothelial growth factor (VEGF) protein and mRNA levels in the myocardial tissue, and anti-CD31 antibody staining by immunohistochemistry was employed to explore whether QYDP exerted an effect on cardiac angiogenesis.ResultsQYDP effectively attenuated cardiac dysfunction and cardiac muscle fibers disruption in Doxo treated mice. Moreover, QYDP reduced myocardial apoptosis and myocardial fibrosis in Doxo treated mice, accompanied with elevated protein levels of VEGF and enhancement of myocardial microvessel density.ConclusionsQYDP could protect against Doxo-induced cardiotoxicity, which may be closely associated with enhanced cardiac angiogenesis. Hence, QYDP could be a promising alternative for the treatment of Doxo-induced cardiotoxicity.

A pilot study to elucidate effects of artificial selection by size on the zebrafish (Danio rerio) fast skeletal muscle transcriptome

Fish size is a complex trait determined by the interaction of environmental and genetic factors. While evidence exists that fish final length and size are partially determined by muscle fibre structure. However, the molecular basis behind final body size and muscle fibre composition remains yet to be fully understood. Here we use the fish model zebrafish (Danio rerio) to explore the molecular mechanisms involved in muscle fibre number, muscle growth and their role on animal size determination. In order to do so, we used two lines of zebrafish artificially selected by Amaral and Johnston 2012 for body length to obtain large (L) and small (S) genetic lineages. After selection animals from the L-lineage were significantly larger than individuals from the S-lineage (+6.6%, +6.7% and + 5.5% for standard, total and fork lengths) and had larger and higher number of muscle fibres (+15% and + 24% on average fibre area and fibre number respectively) while individuals from S-lineage showed a higher fibre density (+17%). RNAseq analysis on fast skeletal muscle revealed differences in gene expression, splice variants (SV) abundance and single nucleotide polymorphism (SNPs) retention between lineages, indicating the complexity of the molecular processes involved in the determination of the trait. We found that animals from the L-lineage showed an enrichment in genes related to the dystroglycan complex (GO:0016011) while genes related to the proteasome (GO:0022624), sarcomere (GO:0030017), muscle homeostasis (GO:0046716) and response to stress (GO:0006950) were enriched on the S-lineage. At individual gene level we also found differences in expression, SV or/and SNPs retention for some key genes involved in muscle development such as mef2ca, mef2cb, stac3, map14a and components of the circadian network (per1a, per1b, per3 and cry2b). These preliminary results provide an initial insight of the molecular changes induced by artificial selection for size, that could aid future studies related to determination of fish growth.

Calixmexitil: Calixarene-based Cluster of Mexiletine with Amplified Anti-myotonic Activity as A Novel Use-dependent Sodium Channel Blocker.

Mexiletine as the first choice drug in myotonia treatment is a chiral sodium channel blocker clinically used in its racemic form. The phenolic structure of this drug, prompted us to design its novel calix[4]arene-based cluster in a chalice-shaped structure. Therefore, the present study reports the synthesis and in-vitro anti-myotonic activity of the chalice-shaped cluster of mexiletine (namely calixmexitil) in comparison to its simple drug unit (mexitil) as the reference medication. The synthetic route included chemical modification of the calix[4]arene structure by grafting four 2-aminopropoxy moieties at the lower rim of the scaffold. Electrophysiological tests were performed for the determination of test compounds abilities to act as sodium channel blockers in inhibiting sodium currents (in use-dependent manner) in single skeletal muscle fibers. The experimental results showed an amplified (10-fold) potency in producing phasic block as an indication of the anti-myotonic activity and improved (3-fold) potency in producing use-dependent block for the cluster (calixmexitil) in relation to its monomer (mexiletine). The potency in producing phasic block and use-dependent block are two main factors to describe dose range, drug affinity, and side effects of an anti-myotonic agent. Therefore, compared to mexiletine, calixmexitil with these improved factors can be considered as a “selective” anti-myotonic agent with low dose range. These improved pharmaceutical effects are maybe attributed to clustering effect and improved interaction of four impacted mexiletine units of the cluster with the sodium channels’ structure in skeletal muscle fibers.

493 The Influence of Muscle Fiber Structure on Meat Palatability.

493 The Influence of Muscle Fiber Structure on Meat Palatability.

Morphological and pathological changes of larynx after severe laryngeal burn in dogs and their relationship with laryngostenosis

Objective: To investigate the morphological and pathological changes of the larynx after severe laryngeal burn in dogs and their relationship with laryngostenosis. Methods: Eighteen healthy, male beagle dogs were assigned into control group, immediately after injury group, and 2, 4, 6, and 8 weeks after injury groups according to the random number table, with 3 dogs in each group. Dogs of injury group inhaled saturated steam through mouth for 5 seconds to reproduce severe laryngeal burn. Tracheotomy and intubation were performed immediately after injury, and 400 000 U/d penicillin was intravenously infused for 1 week. The feeding, activity, and vocalization of dogs in each group after injury were observed until they were sacrificed. Immediately after injury and 2, 4, 6, and 8 weeks after injury, the laryngeal morphology of the dogs in corresponding time point groups were observed by endoscope. After the observation, the dogs in each injury group were sacrificed, and the laryngeal tissue was taken. The epiglottis, glottis, and cricoid cartilage were collected to make full-thickness tissue slice, respectively, and their pathological changes were observed with hematoxylin and eosin staining. The dogs of control group were not specially treated, and their life activities, laryngeal morphological and pathological changes were observed. Results: (1) The dogs of control group had normal feeding, activities, and vocalization. All the dogs in injury group survived until they were sacrificed, and their feeding, activities, and vocalization were obviously reduced after injury compared with those of control group. The dogs of 2, 4, 6 and 8 weeks after injury groups ate and moved normally 2 weeks after injury but vocalized abnormally in frequency and volume compared with those of control group, which lasted until they were sacrificed. (2) The dog's laryngeal mucosa in control group was complete and pink, without obvious exudation. The laryngeal mucosa of the dog in immediately after injury group was pale and edematous, with obvious exudation, local ulceration, necrosis, and exfoliation, and dilated microvessels on the surface. The laryngeal mucosa of the dogs in 2 weeks after injury group was pale, edematous, and oozed less than that of immediately after injury group, and the glottis was blocked by an obviously extruding mass. The paleness and edema of laryngeal mucosa were significantly reduced in the dogs of 4 weeks after injury group compared with those of 2 weeks after injury group, without dilated microvessel, and the glottic extruding mass was obviously smaller than that of 2 weeks after injury group. The sizes of glottic mass were similar between the dogs of 6 and 8 weeks after injury groups, which were obviously smaller than that in 4 weeks after injury group. (3) In the dogs of control group, the epithelial cells of epiglottis, glottis, and cricoid cartilage were normal in morphology, the proper glands were visible in the intrinsic layer, and the muscle fibers and the chondrocytes were normal in morphology. In the dogs of immediately after injury group, large sheets of epiglottis epidermis exfoliated, the epithelial cells were swollen and necrotic, the intrinsic glands were atrophic and necrotic, and the chondrocytes were degenerated and necrotic. The epidermis of the glottis partially exfoliated, the epithelial cells were swollen and necrotic, the intrinsic glands were atrophic and necrotic, the muscle fibers were partially atrophic and fractured, and the vacuolar chondrocytes were visible. The cricoid cartilage epidermis was ablated, the epithelial cells were swollen, the intrinsic layer and submucosal layer were slightly edematous, and the morphological structure of glands, chondrocytes, and muscle fibers were normal. In the dogs of 2 weeks after injury group, the epiglottis epidermis was completely restored, a small amount of glands in the intrinsic layer were repaired, and obsolete necrotic chondrocytes and new chondrocytes could be seen. A large number of fibroblasts, new capillaries, and inflammatory cells infiltration were observed in the epidermis of glottis, and intrinsic layer glands were repaired. The cricoid cartilage epidermis was repaired intactly, and there was no edema in the intrinsic layer. In the dogs of 4 weeks after injury group, the epiglottis intrinsic layer glands were further repaired compared with those of 2 weeks after injury group, and new chondrocytes were seen in the submucosa of the glottis. The condition of cricoid cartilage was consistent with that of control group. The dog's epiglottis, glottis, and cricoid cartilage were similar between the 6 and 8 weeks after injury groups, and no significant change was observed compared with those of 4 weeks after injury group. Conclusions: The morphological changes of larynx after severe laryngeal burn in dogs include mucosa detachment and necrosis, and mass blocking glottis. Pathological changes include epidermis shedding and necrosis, gland atrophy and necrosis, vascular congestion and embolism, chondrocytes degeneration, necrosis and proliferation, even local granulation tissue formation and cartilaginous metaplasia. These results may be the cause of laryngostenosis after laryngeal burn.

Effect of synbiotic dietary supplementation on histological and histopathological parameters of Pectoralis major muscle of broiler chickens

Bioactive substances may constitute an alternative to antibiotics. Probiotics are mixtures of microorganisms that enhance the effectiveness and yield of nutrient absorption by competing for the substrate against pathogens that may cause intestinal infections. Prebiotics are organic substances which include complex carbohydrates and have an influence on the growth and activity of desirable intestinal microflora. Synbiotics are a combination of both of them. The aim of this study was to analyze the impact of synbiotics added to commercial feed on Pectoralis major muscle microstructure in broiler chickens. Research material consisted of 240 one-day-old Ross 308 female chicks. Birds were divided into 2 groups, 12 broilers each (replicated 10 times). The control group (C) was fed a commercial diet, and the SYN group was fed the same diet with added synbiotic: 0.8% of prebiotic RFO (raffinose family oligosaccharides) extracted from lupin seeds and 1% of probiotic Lavipan&lt;sup&gt;®&lt;/sup&gt;. Birds were slaughtered at day 42. Immediately after slaughter, samples of the Pectoralis major muscle for histological analysis were taken and frozen in liquid nitrogen. The staining procedures performed were: hematoxylin and eosin staining to evaluate fibre diameter and histopathological changes, oil red staining to determine intramuscular fat content, NADH-TR (tetrazolium reductase) activity to distinguish muscle fibre types and alkaline phosphatase reaction for counting the number of capillaries. The tendency to reduced muscle fibre diameter in chickens supplemented with synbiotics indicates an increase in muscle fibre density, which gives meat a more delicate structure. When assessing the occurrence of histopathological changes, significantly more fibre splitting was observed in the control group. Moreover, the positive effect of feed supplementation with synbiotics on muscle microvascularization could have an important practical meaning, because low physical activity of chickens during rearing may lead to ischemic muscles, increased changes in the structure of muscle fibres, and reduction of meat quality.

Umbilical cord blood-mesenchymal stem cells and carvedilol reduce doxorubicin- induced cardiotoxicity: Possible role of insulin-like growth factor-1.

In this study, we tried to demonstrate the effects of adding human umbilical cord blood mesenchymal stem cells (hUCB-MSCs) to carvedilol in improving the doxorubicin- induced cardiotoxicity in rats. Rats were randomly divided into four groups: group 1: control group, group 2: doxorubicin untreated group, group 3: rats injected with doxorubicin and received carvedilol, and group 4: rats injected with doxorubicin and received carvedilol and stem cell-treated. Electrocardiography (ECG) was performed to assess cardiac function after animals were sacrificed. Cardiac muscle sections were examined histologically using H&E, Masson trichrome and immunohistochemically using caspase 3 immunostaining. The morphometric and statistical analysis was performed. Levels of malondialdehyde (MDA), superoxide dismutase (SOD), insulin-like growth factor (IGF-1), and vascular endothelial growth factor (VEGF) were measured. We concluded that combination of hUCB-MSCs and carvedilol markedly improves histological and immunohistochemical structure of cardiac muscle fibers and restores cardiac function in doxorubicin- induced cardiotoxicity in rats.

Effect of Melatonin on Rat Heart Mitochondria in Acute Heart Failure in Aged Rats.

Excessive generation of reactive oxygen species (ROS) in mitochondria and the opening of the nonselective mitochondrial permeability transition pore are important factors that promote cardiac pathologies and dysfunction. The hormone melatonin (MEL) is known to improve the functional state of mitochondria via an antioxidant effect. Here, the effect of MEL administration on heart mitochondria from aged rats with acute cardiac failure caused by isoprenaline hydrochloride (ISO) was studied. A histological analysis revealed that chronic intake of MEL diminished the age-dependent changes in the structure of muscle fibers of the left ventricle, muscle fiber swelling, and injury zones characteristic of acute cardiac failure caused by ISO. In acute heart failure, the respiratory control index (RCI) and the Ca2+ retention capacity in isolated rat heart mitochondria (RHM) were reduced by 30% and 40%, respectively, and mitochondrial swelling increased by 34%. MEL administration abolished the effect of ISO. MEL partially prevented ISO-induced changes at the subunit level of respiratory complexes III and V and drastically decreased the expression of complex I subunit NDUFB8 both in control RHM and in RHM treated with ISO, which led to the inhibition of ROS production. MEL prevents the mitochondrial dysfunction associated with heart failure caused by ISO. It was shown that the level of 2′,3′-cyclicnucleotide-3′-phosphodiasterase (CNPase), which is capable of protecting cells in aging, increased in acute heart failure. MEL also retained the CNPase content in RHM both in control experiments and after ISO-induced heart damage. We concluded that an increase in the CNPase level promotes cardioprotection.

Electromyostimulation as an element supporting sports training

Purpose: The aim of the publication is to present the possibilities associated with the use of skeletal muscle electrostimulation as an element supporting sports training. The advantage of this form of training is the performance of specific work by select muscle, especially in less experienced players who can’t isolate a particular muscle during exercise. The electric impulse causes synchronous activation of the muscle contraction in the standard and reproducible conditions, resulting in a much higher level of muscle activity over time.Design / methodology / approach: The effect of muscle electrostimulation on muscle tissue and physiological changes, on the improvement of motor features and the EMS equation for sports training was discussed.Findings: EMS improves the jumping ability (Maffiuletti, Cometti et al. 2000), the maximum muscle strength has also increased (Maffiuletti, Bramanti et al. 2009). Short-term stimulation of low-frequency muscles dramatically shortens the time of getting a contraction. After prolonged stimulation, this result is improved, but it is slower than in the initial phase (Heilmann and Pette 1979). A series of suitable treatments leads to the enlargement of the area of the muscle section, a significant increase in the maximum strength and increase in muscle activation (Gondin, Guette et al. 2005, Kästner, Braun et al. 2015). Recently, it has been shown that EMS regenerates skeletal muscle by reducing the oxidative status in satellite cells muscle hypertrophy and the formation of new myofibrils (Di Filippo, Mancinelli et al. 2017). EMS as a sports training is similar to 4-fold longer training with high intensity exercises (Kemmler, Teschler et al. 2016).Research and practical limitations / implications: Due to reports that EMS affects muscle regeneration, you can use this method as part of wellness during the journey, when other forms are not available or as a short-term training.Originality / value: In summary, a properly selected series of skeletal muscle electrostimulation may affect muscle strength, muscle mass, jumping, speed and endurance as well as changing the structure of muscle fibers.

Rigor bonds cause reduced sarcomeric volume in skinned porcine skeletal muscle under PSE-like conditions

Effects of rigor cross-bridge attachment on water holding in PSE-like conditions were investigated. A new model using permeabilised/skinned porcine longissimus thoracis et lumborum muscle fibres was established to study effects of varied pH, temperature and the presence of rigor bonds on the muscle fibre structure. Preparations were exposed during 30min to different temperatures (22 and 38°C) and pH (7.0 and 5.5) in relaxed and rigor states, followed by evaluation of active force and filament lattice spacing (using small angle X-ray scattering) at standard pH (7.0) and temperature (22°C) conditions. A significant reduction of active force and filament spacing was observed after treatment in rigor at denaturing (38°C, pH5.5) conditions. The present study show that rigor bond attachment under denaturing conditions leads to a compressed interfilamental space, loss of sarcomeric water and affected contractile function.

The two mutations of actin–myosin interface and their effect on the dynamics, structures, and functions of skeletal muscle actin

Congenital myopathy is a broad category of muscular diseases with symptoms appearing at the time of birth. One type of congenital myopathy is Congenital Fiber Type Disproportion (CFTD), a severely debilitating disease. The G48D and G48C mutations in the D-loop and the actin–myosin interface are the two causes of CFTD. These mutations have been shown to significantly affect the structure and function of muscle fibers. To the author’s knowledge, the effects of these mutations have not yet been studied. In this work, the power stroke structure of the head domain of myosin and the wild and mutated types of actin were modeled. Then, a MD simulation was run for the modeled structures to study the effects of these mutations on the structure, function, and molecular dynamics of actin. The wild and mutated actins docked with myosin showed differences in hydrogen bonding patterns, free binding energies, and hydrogen bond occupation frequencies. The G48D and G48C mutations significantly impacted the conformation of D-loops because of their larger size compared to Glycine and their ability to interfere with the polarity or hydrophobicity of this neutralized and hydrophobic loop. Therefore, the mutated loops were unable to fit properly into the hydrophobic groove of the adjacent G-actin. The abnormal structure of D-loops seems to result in the abnormal assembly of F-actins, giving rise to the symptoms of CFTD. It was also noted that G48C and G48D did not form hydrogen bonds with myosin in the residue 48 location. Nevertheless, in this case, muscles are unable to contract properly due to muscle atrophy.

Physical Exercise for Muscle Atrophy.

The most direct characteristic of muscle atrophy is reduction in muscle mass, which is due to increased protein degradation or reduced protein synthesis in skeletal muscle. The loss of muscle mass can directly affect the quality of daily life, prolong the recovery period, and become the main risk factor for chronic diseases. However, there is currently no effective way to prevent and treat this disease, and therefore it is imperative to explore effective therapeutic approaches for muscle atrophy. It is well known that physical exercise is important for maintaining good health and long-term adherence to exercise can reduce the risk of cardiovascular diseases, obesity, and diabetes. It is also well established that exercise training can promote the synthesis of muscle protein and activate signaling pathways that regulate the metabolism and function of muscle fibers. Therefore, exercise can be used as a method to treat muscle atrophy in many of these conditions. Mitochondria play an important role in skeletal muscle homeostasis and bioenergy metabolism. Mitochondria are sensitive to contractile signals, and hence exercise can improve mitochondrial function and promote biosynthesis, which ultimately maintains the healthy state of cells and the whole body. On the other hand, frequent unaccustomed exercise will change the structure and function of skeletal muscle fibers, which is called exercise-induced muscle damage. When the exercise-induced muscle damage happens, it can cause temporary muscle damage and soreness, giving a negative effect on the muscle function.

Diaphragm Atrophy and Weakness in the Absence of Mitochondrial Dysfunction in the Critically Ill.

The clinical significance of diaphragm weakness in critically ill patients is evident: it prolongs ventilator dependency and increases morbidity, duration of hospital stay, and health care costs. The mechanisms underlying diaphragm weakness are unknown, but might include mitochondrial dysfunction and oxidative stress. We hypothesized that weakness of diaphragm muscle fibers in critically ill patients is accompanied by impaired mitochondrial function and structure, and by increased markers of oxidative stress. To test these hypotheses, we studied contractile force, mitochondrial function, and mitochondrial structure in diaphragm muscle fibers. Fibers were isolated from diaphragm biopsies of 36 mechanically ventilated critically ill patients and compared with those isolated from biopsies of 27 patients with suspected early-stage lung malignancy (control subjects). Diaphragm muscle fibers from critically ill patients displayed significant atrophy and contractile weakness, but lacked impaired mitochondrial respiration and increased levels of oxidative stress markers. Mitochondrial energy status and morphology were not altered, despite a lower content of fusion proteins. Critically ill patients have manifest diaphragm muscle fiber atrophy and weakness in the absence of mitochondrial dysfunction and oxidative stress. Thus, mitochondrial dysfunction and oxidative stress do not play a causative role in the development of atrophy and contractile weakness of the diaphragm in critically ill patients.

Sphingosine-1-Phosphate Immobilized on Nanotopographical Scaffolds Improve Myogenic Differentiation.

The skeletal muscle consists of highly aligned dense cables of collagen fibers with nanometer feature size to support muscle fibers. The skeletal myocyte can be greatly affected to differentiate by their surrounding topographical structure. To improve myogenic differentiation, we fabricated cell culture platform that sphingosine-1-phosphate (S1P) which regulated myocyte behavior is immobilized on a biomimetic nanopatterned polyurethaneacrylate (PUA) substrate using 3,4-dihydroxyphenylalanine (L-DOPA) for providing topographical and biological cues synergistically. In the present study, we hypothesized that cultured C2C12 cells can be induced to synergistically promote myogenic differenntiation on nanopatterned PUA-L-DOPA-S1P. We confirmed that nanopatterned PUA-L-DOPA-S1P has high hydrophilicity with a suitable range of water contact angle and small intensity of phosphate peak (P2p) by analyses of water contact analyzer and X-ray photoelectron spectroscopy. In addition, C2C12 cells culured on nanopatterned PUA-L-DOPA-S1P has well-oriented and organized myodubes formed with greater expression of myogenic regulatory factors such as MyoD and MyoG comapred to flat PUA groups. This functional platform which is not only provided topographical and biological cues has a suitable potential function to apply muscle cell niche as similar structure of muscle fiber but also utilized cell behavior within tissue engineered scaffolds and cellular microenvironment.