Ultrastructure Of Muscle Fibers Research Articles

Comparative study on the quality of wild and ecologically farmed large yellow croaker through on-site synchronous sampling from the Nanji Archipelago in the East China Sea

With consumers demanding higher quality in fish products, ecologically farmed fish are increasingly favored due to their quality being close to that of wild fish. However, the differences between the ecologically farmed and wild fish remain largely unclear. In the present study, the wild and ecologically farmed large yellow croakers of the same size were captured simultaneously from the same marine area around Nanji islands (27.479°E, 121.052°N). Then, synchronous tests were conducted to evaluate quality to clarify the key quality parameters that differentiate between the wild and farmed fish. We obtained 49 quality parameters after orthogonal partial least squares discriminant analysis (OPLS-DA) with variable importance in projection (VIP) scores >1 and p < 0.05 using 307 indicators related to 121 length ratios, 4 body color indicators, 5 muscle fiber characteristic indicators, 87 nutrition quality parameters, 40 taste parameters, and 50 volatile compounds. Compared to the farmed fish, the wild fish exhibited a more yellow skin color, higher levels of carotenoids, and a more streamlined conical shape. Changes in histology and ultrastructure of muscle fibers were noted, including increased muscle fiber density and the ratio of fiber area to gap, as well as reduced I band width, observed in the wild fish. The wild fish had high nutritional value of fatty acids and minerals and low nutritional value of amino acids, as reflected by higher levels of C22: 6n3 (DHA), Σn-3 PUFA (polyunsaturated fatty acids), Σn-3/Σn-6 PUFA, Na (sodium), K (potassium), Fe (iron), and Se (selenium), and lower values of ΣMUFA (monosaturated fatty acids), Σn-6 PUFA, TI (thrombogenic index), amino acid and chemistry scores of isoleucine, ΣEAA/ΣTAA (essential amino acid/ total amino acid), and ΣTAA/ΣNEAA (total amino acid/non-essential amino acid) in the muscles of the wild fish. The wild fish muscle showed high levels of hydrolyzed glycine and proline and free methionine, and low levels of free glycine and proline, indicating a propensity for collagen synthesis. Despite significant differences in the contents of fourteen flavor substances of free amino acids, 5′-nucleotides, and volatile compounds, their concentrations were notably below the corresponding threshold and contributed minimally to flavor, suggesting that the wild and farmed fish shared similar flavor characteristics. In summary, this study reveals the quality differences between ecologically farmed and wild large yellow croaker based on on-site synchronous sampling, providing a theoretical foundation for further enhancing the quality of this species.

Comparative study on the morphological characteristics, nutritional quality, and tastes of large yellow croaker from five cage culture areas: Relay farming improved fish quality

Relay culture of large yellow croaker from Fujian to Zhejiang is a good model for improved fish quality. However, there is a scarcity of information regarding the comprehensive evaluation of quality alterations following relay culture. In the present study, the large yellow croaker from Ningde (ND) was transferred to net cages in Dongtou (DT), Nanji (NJ), Dongji (DJ) and Dacheng (DC) for continued culture. The 15-month-old fish from ND, DJ, DC, DT, and NJ were sampled on-site for a subsequent comparative study on the morphological characteristics, nutritional quality, and tastes. Results showed that the fish from DJ, DC, DT, and NJ had a lower condition factor (CF) and a higher ratio of body length to height (L/H) than those from ND. The fish from DJ, DC, DT, and NJ, at rates of 77.8%, 91.3%, 95.7%, and 100%, exhibited different geometric morphometrics from those from ND using 10 typical landmarks and Morpho J software. Ralay culture also significantly affected the histology and ultrastructure of muscle fibers, as reflected by an increase in the muscle fiber density and decreases in the ratio of fiber area to gap, I band width, and sarcomere length in the relay culture fish compared to the ND fish. The relay culture fish showed low lipid content and high moisture content. Relay culture also significantly affected the levels of some nutritional composition, including deceases in the levels of hydrolyzed glycine, C16:0, C18:1n9c, C18:2n6c, Σn-6 PUFA (polyunsaturated fatty acids), Fe (iron), Mn (manganese), and Co (cobalt), and increases in the levels of C20:5n3 (EPA, eicosapentaenoic acid), C22:6n3 (DHA, docosahexaenoic acid), C18:0, Σn-3/Σn-6 PUFA, Σn-3 PUFA, Al (aluminum), Se (selenium), Na (sodium), and Ca (calcium). The levels of taste substances such as guanosine monophosphate (GMP) and most flavor amino acids sharply declined after relay culture. However, the ratio of taste activity value (TAV) of ΣDAA to ΣBAA (delicious amino acids/bitter amino acids) in the DT and NJ fish was higher than that in the ND fish. Significant negative relationships between market price and quality parameters were found, including CF, crude lipid, C18:1n9c, C18:2n6c, Σn-6 PUFA, Fe, Mn, and TAV of GMP, whereas there were positive relationships between market price and 4 quality parameters such as L/H, moisture, Σn-3/Σn-6 PUFA, and the ratio of TAC of ΣDAA to ΣBAA. In conclusion, relay culture improved large yellow croaker quality by changes in morphological characteristics, nutritional quality, and tastes, which provides a theoretical basis for quality improvement.

Impaired muscle strength is associated with ultrastructure damage in myositis

The muscle fiber ultrastructure in Idiopathic Inflammatory Myopathies (IIM) has been scarcely explored, especially in Inclusion Body Myositis. The aim of this study was to implement the Scanning Electron Microscopy (SEM) in a small cohort of IIM patients, together with the characterization of immunological profile for a better understanding of the pathophysiology. For immunological profile characterization, we identified the presence of autoantibodies (Ro-52, OJ, EJ, PL7, PL12, SRP, Jo-1, PMScl75, PMScl100, Ku, SAE1, NXP2, MDA5, TIF1γ, Mi-2α, Mi-2β) and quantified cytokines (IL-1β, IFN-α2, IFN-γ, TNF-α, IL-6, IL-10, IL-12p70, IL-17A, IL-18, IL-23, IL-33) and chemokines (CCL2, CXCL8). The histological analysis was made by hematoxylin–eosin staining while the muscle fiber ultrastructure was characterized by SEM. We observed changes in the morphology and structure of the muscle fiber according to muscle strength and muscle enzymes. We were able to find and describe muscle fiber ultrastructure with marked irregularities, porosities, disruption in the linearity and integrity of the fascicle, more evident in patients with increased serum levels of muscle enzymes and diminished muscle strength. Despite the scarce reports about the use of SEM as a tool in all clinical phenotypes of IIM, our work provides an excellent opportunity to discuss and reframe the clinical usefulness of SEM in the diagnostic approach of IIM.

The ultrastructure of muscle fibers and satellite cells in experimental autoimmune encephalomyelitis after treatment with transcranial magnetic stimulation

ABSTRACT In this study, we investigated the effect of transcranial magnetic stimulation (TMS) on the ultrastructure of muscle fibers and satellite cells in rats with experimental autoimmune encephalomyelitis (EAE). EAE-induced animals were treated with TMS (60 Hz at 0.7 mT) for 2 hours in the morning, once a day, 5 days a week, for 3 weeks, starting on day 15 post-immunization. The rats were sacrificed on day 36 post-immunization, and the soleus muscles were evaluated by light microscopy and transmission electron microscopy. Findings were compared with a non-treated EAE group. Electron microscopy analysis showed the presence of degenerated mitochondria, autophagic vacuoles, and altered myofibrils in non-treated EAE group. This correlates with the presence of acid phosphatase activity in muscle fibers and core-targetoid lesions with desmin immunohistochemistry. Most myonuclei in the EAE group showed apoptotic features. In contrast, EAE induced-TMS treated animals had less ultrastructural changes in the mitochondria and the myofibrils, together with less frequent apoptotic nuclear features. Peripheral desmin+ protrusions, as a marker of active satellite cells, were significantly increased in TMS-treated group. This correlates ultrastructurally with the presence of active features in satellite cells in the TMS group. In conclusion, the attenuation of ultrastructural alterations in muscle fibers and activation response of satellite cells caused by EAE indicated that skeletal muscle had a regenerative response to TMS.

Effects of repeated deboning on structure, composition, and gelling properties of silver carp surimi.

Surimi is produced from the various sequences of filleting, deboning, washing, dehydrating, blending with cryprotectant, and freezing. Deboning, after which fish flesh is minced and separated from bone, skin, etc., is a vital step in the surimi production. In this study, effects of repeated deboning on yield, structure, composition, and gelling properties of silver carp surimi were investigated. Surimi yield increased rapidly from 10% to 23% as the cycle of repeated deboning was increased from one to three, and then slowly increased up to 26%. As the cycle increased, cellular structure and ultrastructure of muscle fibers progressively fractured. Contents of fat, cathepsins, heme proteins, and transglutaminase of surimi obviously increased and then decreased. Three-dimensional network of surimi gel without setting (NS gel) became more porous with the increase of cycles. It became more compact, and then turned to aggregated forms with lower homogeneity, for the surimi gel with setting (WS gel). Correspondently, the NS gel textural values gradually decreased with the cycles, while the WS gel textural values increased up to three cycles and then decreased. Regardless of setting, whiteness of surimi gels decreased and then increased with the cycles. Our results suggested that structure and compositions of surimi changed with the cycle of repeated deboning, which affected gelling properties of surimi. It is recommended to debone three or four cycles in silver carp surimi production. © 2022 Society of Chemical Industry.

Effects of acupuncture on endoplasmic reticulum pathway in exercise-induced skeletal muscle damage in rats and its mechanism

Objective: To observe the effects of acupuncture on the endoplasmic reticulum (ER) functional enzymes sarcoplasmic reticulum Ca2+-ATPase (SERCA), protein disulfide isomerase (PDI), glucose-regulated protein 78(GRP78) and PERK pathways in rats with exercise-induced skeletal muscle damage, and to explore the mechanisms of acupuncture in preventing and treating exercise-induced skeletal muscle damage. Methods: Eight-week-old male SD rats were randomly divided into control group (group C, n=6), exercise group (group E, n=30), acupuncture group (group A, n=30) and exercise acupuncture group (group EA, n=30). Among them, the E and EA group were established an exercise-induced skeletal muscle damage model by a single eccentric exercise, and acupuncture intervention was applied 0.5 cm above the Achilles tendon of the rat's calf immediately after EA exercise, and in group A, acupuncture intervention was applied during the same period. Each group was divided into 0 h/12 h/24 h/48 h/72 h (n=6) according to different sampling time points after exercise and acupuncture intervention, and soleus muscle was collected at the corresponding time for index test. The ultrastructure of muscle fibers was observed by transmission electron microscopy; the contents of SERCA and PDI were determined by ELISA; and the expressions of ER stress marker proteins GRP78 and p-PERK and p-eIF2α were detected by Western blot. Results: Compared with group C, there were no significant differences in the indicators of group A at all time points (P＞ 0.05), the ultrastructure of muscle fibers in group E showed different damages, SERCA content was significantly decreased from 0 h to 48 h (P＜0.05), PDI content was significantly increased from 0 h to 72 h (P＜0.05), GRP78 expression was significantly increased from 0 h to 72 h (P＜0.05), p-PERK expression was significantly increased from 0 h to 24 h (P＜0.05), and p-eIF2α expression was consistent with p-PERK. Compared with the corresponding times in group E, the ultrastructure of muscle fibers in group EA was significantly alleviated, SERCA content was significantly increased from 48 h and 72 h (P＜0.05), PDI content was significantly increased from 0 h to 72 h (P＜0.05), and GRP78 expression was significantly decreased from 0 h to 72 h (P＜0.05). Conclusion: Acupuncture can effectively ameliorate exercise-induced skeletal muscle damage and alleviate ER stress after a large load eccentric exercise. The mechanism of them may be related to the up-regulation of protein disulfide isomerase PDI and the inhibition of ER stress PERK pathway.

Mandibular muscle troponin of the Florida carpenter ant Camponotus floridanus: extending our insights into invertebrate Ca2+ regulation.

Ants use their mandibles for a variety of functions and behaviors. We investigated mandibular muscle structure and function from major workers of the Florida carpenter ant Camponotusfloridanus: force-pCa relation and velocity of unloaded shortening of single, permeabilized fibres, primary sequences of troponin subunits (TnC, TnI and TnT) from a mandibular muscle cDNA library, and muscle fibre ultrastructure. From the mechanical measurements, we found Ca2+-sensitivity of isometric force was markedly shifted rightward compared with vertebrate striated muscle. From the troponin sequence results, we identified features that could explain the rightward shift of Ca2+-activation: the N-helix of TnC is effectively absent and three of the four EF-hands of TnC (sites I, II and III) do not adhere to canonical sequence rules for divalent cation binding; two alternatively spliced isoforms of TnI were identified with the alternatively spliced exon occurring in the region of the IT-arm α-helical coiled-coil, and the N-terminal extension of TnI may be involved in modulation of regulation, as in mammalian cardiac muscle; and TnT has a Glu-rich C-terminus. In addition, a structural homology model was built of C.floridanus troponin on the thin filament. From analysis of electron micrographs, we found thick filaments are almost as long as the 6.8μm sarcomeres, have diameter of ~ 16nm, and typical center-to-centerspacing of ~ 46nm. These results have implications for the mechanisms by which mandibular muscle fibres perform such a variety of functions, and how the structure of the troponin complex aids in these tasks.

Consequences of being phenotypically mismatched with the environment: rapid muscle ultrastructural changes in cold-shocked black-capped chickadees (Poecile atricapillus).

Phenotypic flexibility has received considerable attention in the last decade; however, whereas many studies have reported amplitude of variation in phenotypic traits, much less attention has focused on the rate at which traits can adjust in response to sudden changes in the environment. We investigated whole animal and muscle phenotypic changes occurring in black-capped chickadees (Poecile atricapillus) acclimated to cold (-5°C) and warm (20°C) temperatures in the first 3 h following a 15°C temperature drop (over 3 h). Before the temperature change, cold-acclimated birds were consuming 95% more food, were carrying twice as much body fat, and had 23% larger pectoralis muscle fiber diameters than individuals kept at 20°C. In the 3 h following the temperature drop, these same birds altered their pectoralis muscle ultrastructure by increasing the number of capillaries per fiber area and the number of nuclei per millimeter of fiber by 22%, consequently leading to a 22% decrease in myonuclear domain (amount of cytoplasm serviced per nucleus), whereas no such changes were observed in the warm-acclimated birds. To our knowledge, this is the first demonstration of such a rapid adjustment in muscle fiber ultrastructure in vertebrates. These results support the hypothesis that chickadees maintaining a cold phenotype are better prepared than warm-phenotype individuals to respond to a sudden decline in temperature, such as what may be experienced in their natural wintering environment.

Seasonal muscle ultrastructure plasticity and resistance of muscle structural changes during temperature increases in resident black-capped chickadees (Poecile atricapillus) and rock pigeons (Columba livia)

Resident birds in temperate zones respond to seasonally fluctuating temperatures by adjusting their physiology, such as changes in basal metabolic rate or peak metabolic rate during cold exposure, or altering their organ sizes, so as to match the thermogenic requirements of their current environment. Climate change is predicted to cause increases in the frequency of heat and cold wave events, which could increase the likelihood that birds will face an environmental mismatch. Here, we examined seasonality and the effects of acute and chronic heat shock to 33°C and subsequent recovery from heat shock on the ultrastructure of the superficial pectoralis muscle fiber diameter, myonuclear domain (MND) and capillary density in two temperate bird species of differing body mass, the black-capped chickadee (Poecile atricapillus) and the rock pigeon (Columba livia). We found that muscle fiber ultrastructure did not change with heat treatment. However, in black-capped chickadees, there was a significant increase in fiber diameter in spring phenotype birds compared with summer phenotype birds. In rock pigeons, we saw no differences in fiber diameter across seasons. Capillary density did not change as a function of fiber diameter in black-capped chickadees, but did change seasonally, as did MND. Across seasons, as fiber diameter decreased, capillary density increased in the pectoralis muscle of rock pigeons. For both species in this study, we found that as fiber diameter increased, so did MND. Our findings imply that these two temperate birds employ different muscular growth strategies that may be metabolically beneficial to each.

Effects of chloride injections and ultrasonic treatment on the microstructure of longissimus lumborum muscle fibers from beef cattle as investigated by atomic force microscopy

ABSTRACTThis study aimed to use atomic force microscopy to compare effects of ultrasound bath, injecting calcium chloride solution and sodium chloride solution on the ultrastructure of muscle fibers and choose the preferred meat tenderizing method. The muscles fibers were tenderized and then scanned by atomic force microscopy. When meat was treated by ultrasound bath (50 W, 100 W, 250 W), CaCl2 injection (400 mM, 500 mM) and NaCl injection (100, 200, 300, 400, 500 mM), the sarcomere length was longer as compared with the control (P < 0.05). In consideration of the consumer demand and other palatability and quality traits of meat, the ultrasound bath could be applied to improve meat tenderness without detrimental effects.

Ultrastructural preservation of tissues and their reaction to the infection with trichinella in the El Plomo mummy: Muscle fiber ultrastructure and trichinosis/mummy of the Cerro El Plomo.

The El Plomo mummy was a pre-Columbian Incan child who was found mummified in the Andes Mountains above an altitude of 17,700 feet. In the environment, natural mummification occurred due to low temperatures and strong winds. Dating measurements (relative dating) by experts from the National Museum of Natural History of Chile established that the mummified body corresponds the Inca period (1,450 to 1,500 AD). In 2003, the body was transferred to the University of Chile Medical School for exhaustive medical examination. Tissue samples from the right quadriceps muscle were extracted and fixed in glutaraldehyde and postfixed in osmium tetroxide to obtain ultrathin sections to be observed by transmission electron microscope. Images were recorded on photographic paper, digitalized and analyzed by experts on morphology. Results showed a preservation of cell boundaries in striated muscle cells, but specific subcellular organelles or contractile sarcomeric units (actin and myosin) were unable to be recognized. However, the classical ultrastructural morphology of the polypeptide collagen type I was preserved intact both in primary and secondary organization. Therefore, we concluded that the process of natural mummification by freezing and strong winds is capable of damaging the ultrastructure of muscle cells and preserving collagen type I intact.

Ultrastructural characteristics of muscular tissue during surgical treatment of patients with ІІІ degree chronic ischemia of lower limb.

Background . Of particular note is the analysis of ultrastructural features of compensatory repair capabilities in terms of muscle ischemic injury developing in several ways: 1) direct induction of angiogenesis; 2) increased survival of muscle fibers; 3) mediated stimulation of muscle-typical differentiation; 4) resistance to apoptotic mechanisms. Objective. The purpose of research was the ultrastructural analysis of anterior tibial muscle in patients with ІІІ degree chronic ischemia of lower limb after direct, indirect and composite revascularization in near-term and long-term postoperative periods. Methods. Patients have been divided into three groups: 1) 37 patients after femoral-tibial reconstruction; 2) 57 patients after indirect revascularization with autotransplantation of bone marrow; 3) 50 patients after composite revascularization of distal part of lower limb. The observation was carried out in the near-term postoperative period and in 2 years. Ultrastructural study of tissue samplings of anterior tibial muscle taken between superior and middle one thirds was carried out. Results. It have been determined that direct revascularization causes the significant improvement ultrastructure of muscle fibers of anterior tibial muscle in all age groups during 6 months after operation, however does not provide the stabilization of positive changes in long-term postoperative period. Indirect revascularization does not change significally structurally-functional condition of components of muscle in near-term postoperative period, however causes the stable normalization of parameters of tissue components due to initiation of neovasculogenesis at patients till 75 years. Conclusion. Composite revascularization allows to receive near-term normalizing effect concerning the studied ultrastructural criteria and to provide its stabilization in the long-term postoperative period.

Automated cardiac sarcomere analysis from second harmonic generation images.

Automatic quantification of cardiac muscle properties in tissue sections might provide important information related to different types of diseases. Second harmonic generation (SHG) imaging provides a stain-free microscopy approach to image cardiac fibers that, combined with our methodology of the automated measurement of the ultrastructure of muscle fibers, computes a reliable set of quantitative image features (sarcomere length, A-band length, thick-thin interaction length, and fiber orientation). We evaluated the performance of our methodology in computer-generated muscle fibers modeling some artifacts that are present during the image acquisition. Then, we also evaluated it by comparing it to manual measurements in SHG images from cardiac tissue of fetal and adult rabbits. The results showed a good performance of our methodology at high signal-to-noise ratio of 20 dB. We conclude that our automated measurements enable reliable characterization of cardiac fiber tissues to systematically study cardiac tissue in a wide range of conditions.

Severe muscle atrophy due to spinal cord injury can be reversed in complete absence of peripheral nerves

In the last years, a new efficient treatment has been developed to treat paralyzed skeletal muscle of patients affected by spinal cord injury (SCI). The capability of the functional electrical stimulation (FES) to improve trophism and in some cases muscle function, are now well documented both in animals after experimental cord lesion, and in humans, generally after traumatic cord lesion. This new findings makes FES an important tool for the rehabilitation of SCI patients. FES stimulation has been proven to be an effective method used to retard muscle atrophy and improve recovery after reinnervation. Sophisticated FES devices have been developed for restoring function in the upper and lower extremities, the bladder and bowel, and the respiratory system of SCI patients. However, there are SCI cases, such as those affected by flaccid paralysis, in which the musculature is not treated with FES rehabilitation therapy. This is because conventional FES apparatuses are designed for direct stimulation of peripheral nerves that need small currents to be depolarized, and are not effective in patients that have lost their peripheral nerves, and, therefore, require higher currents for the direct depolarization of the muscle fibers. Lack of muscle treatment generates, as a secondary problem, a long series of alterations to tissues other than muscle, such as bones (osteoporosis), skin (pressure sores, decubital ulcers), etc., that are a direct consequence of inactivity and poor blood supply to the denervated areas. These complications represent an extremely serious problem for the general health of the injured individuals, who usually have a shorter than normal life span. In the hopes of changing this common belief, an innovative rehabilitation procedure, based on FES, has been developed with the aim of reversing long-lasting muscle atrophy in the muscles of the lower extremities of SCI patients affected by complete lesion of the conus cauda, i.e. that have no peripheral nerves. Experimental and clinical results have shown that electrical stimulation training by long impulses can restore muscle mass, force production and movements even after long lasting complete denervation. Measurements by CT-scans revealed a substantial increase of tight muscle cross sectional area during the first years of FES and muscle function of the lower extremities was restored in some patients sufficiently to allow for supported standing, standing, and even for a few steps to be taken. We have described the ultrastructural changes accompanying the recovery of skeletal muscle in the total absence of either sensory or motor innervation. The results showed a striking structural recovery of muscle fiber ultrastructure in all FES treated patients: the 90% (or more) of the studied fibers recovery from a very profound atrophy under the influence of the electrical stimulation. Restoration of ultrastructure involves all the major apparatuses of muscle fibers, such as the one deputed to muscle activation and Ca2+ handling (ECC apparatus), to contractility (myofibrils), and to metabolic and energy generation tasks (mitochondria). This structural recovery occurs in complete absence of nerve endings, under the influence of muscle activity, and follows pattern that mimics in many aspects normal muscle differentiation as well as recovery after short-term disuse and/or denervation. The present ultra-structural studies are important because they show that, despite the apparent complete loss of specific structure, the long-term denervated fibers maintain their full differentiation program. Reversal of the damages from long-standing denervation in humans may be of significant importance also for the rehabilitation and the general health of SCI patients.

Severe muscle atrophy due to spinal cord injury can be reversed in complete absence of peripheral nerves

In the last years, a new efficient treatment has been developed to treat paralyzed skeletal muscle of patients affected by spinal cord injury (SCI). The capability of the functional electrical stimulation (FES) to improve trophism and in some cases muscle function, are now well documented both in animals after experimental cord lesion, and in humans, generally after traumatic cord lesion. This new findings makes FES an important tool for the rehabilitation of SCI patients. FES stimulation has been proven to be an effective method used to retard muscle atrophy and improve recovery after reinnervation. Sophisticated FES devices have been developed for restoring function in the upper and lower extremities, the bladder and bowel, and the respiratory system of SCI patients. However, there are SCI cases, such as those affected by flaccid paralysis, in which the musculature is not treated with FES rehabilitation therapy. This is because conventional FES apparatuses are designed for direct stimulation of peripheral nerves that need small currents to be depolarized, and are not effective in patients that have lost their peripheral nerves, and, therefore, require higher currents for the direct depolarization of the muscle fibers. Lack of muscle treatment generates, as a secondary problem, a long series of alterations to tissues other than muscle, such as bones (osteoporosis), skin (pressure sores, decubital ulcers), etc., that are a direct consequence of inactivity and poor blood supply to the denervated areas. These complications represent an extremely serious problem for the general health of the injured individuals, who usually have a shorter than normal life span. In the hopes of changing this common belief, an innovative rehabilitation procedure, based on FES, has been developed with the aim of reversing long-lasting muscle atrophy in the muscles of the lower extremities of SCI patients affected by complete lesion of the conus cauda, i.e. that have no peripheral nerves. Experimental and clinical results have shown that electrical stimulation training by long impulses can restore muscle mass, force production and movements even after long lasting complete denervation. Measurements by CT-scans revealed a substantial increase of tight muscle cross sectional area during the first years of FES and muscle function of the lower extremities was restored in some patients sufficiently to allow for supported standing, standing, and even for a few steps to be taken. We have described the ultrastructural changes accompanying the recovery of skeletal muscle in the total absence of either sensory or motor innervation. The results showed a striking structural recovery of muscle fiber ultrastructure in all FES treated patients: the 90% (or more) of the studied fibers recovery from a very profound atrophy under the influence of the electrical stimulation. Restoration of ultrastructure involves all the major apparatuses of muscle fibers, such as the one deputed to muscle activation and Ca2+ handling (ECC apparatus), to contractility (myofibrils), and to metabolic and energy generation tasks (mitochondria). This structural recovery occurs in complete absence of nerve endings, under the influence of muscle activity, and follows pattern that mimics in many aspects normal muscle differentiation as well as recovery after short-term disuse and/or denervation. The present ultra-structural studies are important because they show that, despite the apparent complete loss of specific structure, the long-term denervated fibers maintain their full differentiation program. Reversal of the damages from long-standing denervation in humans may be of significant importance also for the rehabilitation and the general health of SCI patients.

Muscle hypertrophy induced by the Ski protein: cyto‐architecture and ultrastructure

Transgenic mice overexpressing the c-ski proto-oncogene driven by the MSV promoter undergo muscle hypertrophy, most notably fast fibres of the lower limb. This hypertrophy is not accompanied by a correspondingly large increase in force, and individual skinned muscle fibres exhibit a 30% reduction in force per cross-sectional area. In this respect, the MSV ski model is different from most other hypertrophy models and we here aim at describing the mechanisms for the reduced specific force. Cyoarchitecture and ultrastructure of muscle fibres from the fast extensor digitorum longus muscle of 2-3 months old MSV ski mice was studied. In addition to electron microscopy, we used in vivo intracellular injections of myonuclear dye to investigate nuclear number. The number of nuclei did not increase in proportion to size, and consequently nuclear domains were increased compared with wild type. The fraction of the cytoplasm occupied by contractile material was reduced by 18%. In addition we observed poor intracellular alignment of Z-discs. Such staggering has been reported to reduce force in desmin deficient mice, but the amount and distribution of desmin in the MSV ski mice seemed normal. The mitochondria of MSV ski mice showed irregularly spaced cristae that were frequently disrupted. The reduction in specific force observed in MSV ski mice could be explained by a reduced fraction of contractile material and reduced transversal mechanical coupling. The ultrastructural abnormalities could be related to an increase in nuclear domains.

Relative contribution of quantitative and qualitative changes in mitochondria to metabolic compensation during seasonal acclimatisation of rainbow trout Oncorhynchus mykiss

ABSTRACT This study examined whether changes in the properties of mitochondria from red muscle of rainbow trout Oncorhynchus mykiss are accompanied by ultrastructural changes during cold acclimatisation. We compared measurements at five levels of organisation in red muscle of winter-(1 °C) and summer-(16 °C) acclimatised trout. We examined (1) maximal rates of pyruvate and palmitoyl carnitine oxidation by isolated mitochondria, (2) enzymatic activities [cytochrome c oxidase (CCO), citrate synthase (CS), carnitine palmitoyl transferase (CPT) and phosphofructokinase (PFK)] of the muscle and isolated mitochondria, (3) mitochondrial protein content in the muscle, (4) the ultrastructure of muscle fibres, and (5) the cristae surface density of the mitochondria. All variables were measured on each trout sampled. The mitochondria from winter-acclimatised trout possessed higher maximal capacities for the oxidation of pyruvate and palmitoyl carnitine than those from summer-acclimatised trout. Muscle activities of CCO, CS and CPT were greater in winter than in summer trout, whereas the levels of PFK did not differ seasonally. Similarly, the mitochondria from winter trout had elevated levels of CCO, CS and CPT compared with those isolated from summer trout. The cristae surface density of the mitochondria from winter trout (40.2±0.6 μm2μm−3; mean ± S.E.M.) was significantly higher than that from summer trout (36.4±1.2 μm2 μm−3), whereas there was no difference in the mitochondrial volume densities of muscle fibres from winter and summer trout. Thus, the considerable compensation of muscle aerobic capacity at low temperatures in trout is not accompanied by changes in mitochondrial volume density, but rather by shifts in enzyme levels and cristae surface density.

Injury to muscle fibres after single stretches of passive and maximally stimulated muscles in mice.

1. Our purpose was to investigate the initial mechanisms responsible for contraction-induced injury. Most studies of mechanisms of contraction-induced injury have been based on observations made either shortly after many repeated contractions at the peak of fatigue, or days after, at the peak of delayed onset injury. As a result, conclusions based on these studies are complicated by interactions of mechanical and biochemical events, as well as the passage of time. We studied the initial mechanical events associated with contraction-induced injury immediately following single stretches of whole skeletal muscles of mice in situ. 2. We tested the hypothesis that immediately following a single stretch, the severity of contraction-induced injury is a function of both strain and average force. Consequently, the work done to stretch the muscle would be the best predictor of the magnitude of injury. Extensor digitorum longus muscles were adjusted to optimum length for force (L(o)). Passive (not stimulated) and maximally activated muscles were exposed to single stretches of 10, 20, 30, 50 or 60% strain, relative to muscle fibre length (Lf), at a rate of 2 Lf s-1. 3. The magnitude of injury was represented by the force deficit 1 min after the stretch expressed as a percentage of the maximum force prior to the stretch. The occurrence of injury was confirmed directly by electron microscopic analysis of the ultrastructure of muscle fibres that were fixed immediately following single stretches. 4. For active muscles, a single stretch of only 30% strain produced a significant force deficit, whereas for passive muscles, a larger strain was required. Stretches of greater than 50% strain resulted in greater force deficits for passive than for maximally activated muscles. For either condition, the work done to stretch the muscle was the best predictor of the magnitude of injury, accounting for 76% of the variability in the force deficit for maximally activated muscles, and 85% for passive muscles.

Comparative body wall musculature and muscle fibre ultrastructure in branchiobdellidans (Annelida: Clitellata), and their phylogenetic significance

Comparative body wall musculature and muscle fibre ultrastructure in branchiobdellidans (Annelida: Clitellata), and their phylogenetic significance

Ultrastructure of muscle fibers and cells synthesizing DNA in lymph hearts of developing frogs and chick embryos

The ultrastructure of striated muscle fibers and 3H-thymidine (3HTdr)-labeled cells adjacent to them in the lymph hearts of larvae of Rana temporaria, yearling frogs, and 9- to 13-day-old chick embryos was studied by use of electron-microscopic autoradiography. A comparatively high level of differentiation of lymph-heart muscle fibers was observed not only in yearling frogs but also in larvae. Myosatellites occurred in all stages of development. No mitoses were found in muscle fibers. In 9- to 13-day-old chick embryos the myofibers of lymph hearts were somewhat less differentiated than those of the larvae and yearling frogs. Differentiating sarcomeres were often seen in the sarcoplasm of myofibers of chick embryos. The analysis of the ultrastructure of 3HTdr-incorporating cells shows that 2-4 h after the single 3HTdr administration only mononucleated cells devoid of myofilaments are commonly labeled both in tadpoles and chick embryos. When fixation is postponed by 48-70 h, myonuclei frequently become labeled. Thus, the data obtained support the evidence that proliferation and differentiation processes in the developing muscle tissue of the lymph heart of both species studied are mutually exclusive, similar to the situation in differentiating vertebrate skeletal muscle.