Differential morphofunctional characteristics and gene expression in fast and slow muscle of rats with monocrotaline-induced heart failure

Heart failure (HF) is characterized by limited exercise tolerance, skeletal muscle atrophy, a shift toward fast muscle fiber, and myogenic regulatory factor (MRF) changes. Reactive oxygen species (ROS) also contribute to target organ damage in this syndrome. In this study, we investigated and compared morphofunctional characteristics and gene expression in Soleus (SOL--oxidative and slow twitching muscle) and in Extensor Digitorum Longus (EDL--glycolytic and fast twitching muscle) during HF. Two groups of rats were used: control (CT) and heart failure (HF), induced by a single injection of monocrotaline. MyoD and myogenin gene expression were determined by RT-qPCR, and MHC isoforms by SDS-PAGE; muscle fiber type frequency and cross sectional area (CSA) were analyzed by mATPase. A biochemical study was performed to determine lipid hydroperoxide (LH), glutathione peroxidase (GSH-Px), and superoxide dismutase (SOD); myography was used to determine amplitude, rise time, fall time, and fatigue resistance in both muscles. HF showed SOL and EDL muscle atrophy in all muscle fiber types; fiber frequency decreased in type IIC and muscle contraction fall time increased only in SOL muscle. Myogenin mRNA expression was lower in SOL and myoD decreased in HF EDL muscle. LH increased, and SOD and GSH-Px activity decreased only in HF SOL muscle. HF EDL muscle did not present changes in MHC distribution, contractile properties, HL concentration, and antioxidant enzyme activity. In conclusion, our results indicate that monocrotaline induced HF promoted more prominent biochemical, morphological and functional changes in SOL (oxidative and slow twitching muscle). Although further experiments are required to better determine the mechanisms involved in HF pathophysiology, our results contribute to understanding the muscle-specific changes that occur in this syndrome.     

Akt signaling in skeletal muscle: regulation by exercise and passive stretch

Akt/protein kinase B is a serine/threonine kinase that has emerged as a critical signaling component for mediating numerous cellular responses. Contractile activity has recently been demonstrated to stimulate Akt signaling in skeletal muscle. Whether physiological exercise in vivo activates Akt is controversial, and the initiating factors that result in the stimulation of Akt during contractile activity are unknown. In the current study, we demonstrate that treadmill running exercise of rats using two different protocols (intermediate high or high-intensity exhaustive exercise) significantly increases Akt activity and phosphorylation in skeletal muscle composed of various fiber types. To determine if Akt activation during contractile activity is triggered by mechanical forces applied to the skeletal muscle, isolated skeletal muscles were incubated and passively stretched. Passive stretch for 10 min significantly increased Akt activity (2-fold) in the fast-twitch extensor digitorum longus (EDL) muscle. However, stretch had no effect on Akt in the slow-twitch soleus muscle, although there was a robust phosphorylation of the stress-activated protein kinase p38. Similar to contraction, stretch-induced Akt activation in the EDL was fully inhibited in the presence of the phosphatidylinositol 3-kinase inhibitor wortmannin, whereas glycogen synthase kinase-3 (GSK3) phosphorylation was only partially inhibited. Stretch did not cause dephosphorylation of glycogen synthase on GSK3-targeted sites in the absence or presence of wortmannin. We conclude that physiological exercise in vivo activates Akt in multiple skeletal muscle fiber types and that mechanical tension may be a part of the mechanism by which contraction activates Akt in fast-twitch muscles.     

Proteomic and Carbonylation Profile Analysis of Rat Skeletal Muscles following Acute Swimming Exercise

Previous studies by us and other groups characterized protein expression variation following long-term moderate training, whereas the effects of single bursts of exercise are less known. Making use of a proteomic approach, we investigated the effects of acute swimming exercise (ASE) on protein expression and carbonylation patterns in two hind limb muscles: the Extensor Digitorum Longus (EDL) and the Soleus, mostly composed of fast-twitch and slow-twitch fibres, respectively. Carbonylation is one of the most common oxidative modifications of proteins and a marker of oxidative stress. In fact, several studies suggest that physical activity and the consequent increase in oxygen consumption can lead to increase in reactive oxygen and nitrogen species (RONS) production, hence the interest in examining the impact of RONS on skeletal muscle proteins following ASE. Results indicate that protein expression is unaffected by ASE in both muscle types. Unexpectedly, the protein carbonylation level was reduced following ASE. In particular, the analysis found 31 and 5 spots, in Soleus and EDL muscles respectively, whose carbonylation is reduced after ASE. Lipid peroxidation levels in Soleus were markedly reduced as well. Most of the decarbonylated proteins are involved either in the regulation of muscle contractions or in the regulation of energy metabolism. A number of hypotheses may be advanced to account for such results, which will be addressed in future studies.     

Myofibril breakdown during spreading damage. III. Isolated rat muscles

Ultrastructural changes have been studied in fast (EDL) and slow (SOL) isolated muscles of rats during Zenker's degeneration (ZD). The general pattern of ZD is similar in both the muscles and proceeds in the same way as in the fast skeletal muscles of amphibians: vacuolation of the T-system and of the sarcoplasmic reticulum occur prior to necrosis, and then contraction knots are formed. The latter detach from the rest of the fiber, and myofibrils degrade into clots of electron dense material. Differences in the development of ZD in this muscle are as follows: vacuolation is more strongly pronounced in EDL, contraction and supercontraction of sarcomeres being more characteristic of SOL. In this ZD region of both the muscles, additional membranes are found in some intracrystal spaces of mitochondria, this phenomenon occuring more frequently in SOL. Selective lysis of the Z-line during ZD has been detected only in single EDL Fibres.     

Comparison of red and white muscle wet weight changed by age, denervation and morbid states

[Na]i, [K]i and wet weight of the extensor digitrum longus (EDL) and soleus (SOL) muscles of 9- and 52-week-old rats were measured for 7 days after sectioning of the sciatic nerve. The changes in wet weight of the EDL and SOL muscles of rats over 52 weeks and those of morbid state rats were also measured. There was no significant difference in wet weights between the EDL and SOL muscles in infant rats, but the EDL muscle became much heavier than the SOL muscle with aging. The decrease in rate of growth of wet weight of the EDL and SOL muscles caused by denervation, was greater in young rats than in mature rats. In addition, the rate of decrease was greater in the SOL muscles than in the EDL muscles in both young and mature rats. The [Na]i increased while [K]i was decreased by denervation, and the net Na+ increase and the net K+ loss were greater in young rats than in mature rats. The changing rate was more remarkable in the EDL muscles than in the SOL muscles throughout the aging process. During DOCA treatment over 4 weeks, the decrease of muscle wet weight was greater in the EDL muscles. The mechanisms which serve to maintain normal muscle wet weight in the SOL muscle after denervation or treatment with DOCA, were discussed.     

In situ NADH laser fluorimetry of rat fast- and slow-twitch muscles during tetanus

To investigate the variations of oxidation-reduction status of fast- and slow-twitch muscles during intense contractions, we performed in situ NADH laser fluorimetry during 25-s tetanus in extensor digitorum longus (EDL) and in soleus (SOL) muscles of eight Sprague-Dawley rats anesthetized with pentobarbital sodium. At base line the compensated NADH fluorescence (F0) was not significantly different between EDL and SOL. In EDL, tetanic stimulation induced an increase of F0, which rapidly reached a plateau that was 124% over the base-line value and stable until the end of the stimulation. In SOL, after an initial shouldering there was a continuous increase of F0 until the end of tetanus, reaching 275% of the base-line value. After the stimulation the initial rate of recovery was significantly faster in SOL than in EDL. We conclude that during and after intense contraction the variation of NADH content vs. time can be evaluated by in situ NADH laser fluorimetry in different muscle types. This nondestructive method can be helpful to differentiate in situ the various physiological or pathological oxidative capabilities of skeletal muscles.     

Physiological, histological and biochemical properties of rat skeletal muscles in response to hindlimb suspension.

In previous study, we found that the reduced exercise-induced production of reactive oxygen species (ROS) reported in slow-oxidative muscle of hypoxemic rats and also in chronic hypoxemic patients did not simply result from deconditioning. In control rats and after a 3-week period of hindlimb suspension (HS), the slow-oxidative (Soleus, SOL) and fast-glycolytic skeletal muscles (Extensor digitorum longus, EDL) were sampled. We determined the response to direct muscle stimulation (twitch stimulation (TS), Maximal force (Fmax)), twitch amplitude and maximal relaxation rate, tetanic frequency, endurance to fatigue after muscle stimulation (MS), the different fibre types based on their myofibrillar adenosinetriphosphatase (ATPase) activity, and the intra-muscular redox status (Thiobarbituric Acid Reactive Sustances: TBARS, reduced glutathione: GSH, reduced ascorbic acid: RAA). After the 3-w HS period: (1) the contractile properties were modified in SOL only (reduced Fmax and twitch amplitude, increased tetanic frequency); (2) the fibre typology was modified in both muscles (in SOL: increased proportion of IIa and IIc fibres, in EDL: increased proportion of IId/x fibres but decreased proportion of IIb fibres); and (3) only in SOL, the TBARS level increased and the GSH and RAA concentrations decreased at rest and after fatiguing MS. Thus, HS accentuates the exercise-induced ROS production in slow-oxidative muscle in a direction opposite to that measured in chronic hypoxemic rats. This strongly suggests that hypoxemia reduces the ROS production independently from any muscle disuse.     

Morphological aspects of neuromuscular junctions and gene expression of nicotinic acetylcholine receptors (nAChRs) in skeletal muscle of rats with heart failure

HF is syndrome initiated by a reduction in cardiac function and it is characterized by the activation of compensatory mechanisms. Muscular fatigue and dyspnoea are the more common symptoms in HF; these may be due in part to specific skeletal muscle myopathy characterized by reduced oxidative capacity, a shift from slow fatigue resistant type I to fast less fatigue resistant type II fibers and downregulation of myogenic regulatory factors (MRFs) gene expression that can regulate gene expression of nicotinic acetylcholine receptors (nAChRs). In chronic heart failure, skeletal muscle phenotypic changes could influence the maintenance of the neuromuscular junction morphology and nAChRs gene expression during this syndrome. Two groups of rats were studied: control (CT) and Heart Failure (HF), induced by a single intraperitoneal injection of monocrotaline (MCT). At the end of the experiment, HF was evaluated by clinical signs and animals were sacrificed. Soleus (SOL) muscles were removed and processed for morphological, morphometric and molecular NMJ analyses. Our major finding was an up-regulation in the gene expression of the alpha1 and epsilon subunits of nAChR and a spot pattern of nAChR in SOL skeletal muscle in this acute monocrotaline induced HF. Our results suggest a remodeling of nAChR alpha1 and epsilon subunit during heart failure and may provide valuable information for understanding the skeletal muscle myopathy that occurs during this syndrome.     

Maternal protein restriction induce skeletal muscle changes without altering the MRFs MyoD and myogenin expression in offspring

Stimuli during pregnancy, such as protein restriction, can affect morphophysiological parameters in the offspring with consequences in adulthood. The phenomenon known as fetal programming can cause short- and long-term changes in the skeletal muscle phenotype. We investigated the morphology and the myogenic regulatory factors (MRFs) MyoD and myogenin expression in soleus, SOL; oxidative and slow twitching and in extensor digitorum longus, EDL; glycolytic and fast twitching muscles in the offspring of dams subjected to protein restriction during pregnancy. Four groups of male Wistar offspring rats were studied. Offspring from dams fed a low-protein diet (6?% protein, LP) and normal protein diet (17?% protein, NP) were euthanized at 30 and 112?days old, and their muscles were removed and kept at ?80?°C. Muscles histological sections (8?μm) were submitted to a myofibrillar adenosine triphosphatase histochemistry reaction for morphometric analysis. Gene and protein expression levels of MyoD and myogenin were determined by RT-qPCR and western blotting. The major findings observed were distinct patterns of morphological changes in SOL and EDL muscles in LP offspring at 30 and 112?days old without changes in MRFs MyoD and myogenin expression. Our results indicate that maternal protein restriction followed by normal diet after birth induced morphological changes in muscles with distinct morphofunctional characteristics over the long term, but did not alter the MRFs MyoD and myogenin expression. Further studies are necessary to better understand the mechanisms underlying the maternal protein restriction response on skeletal muscle.     

Glucocorticoid-induced glycogen increases in extensor digitorum longus and soleus grafts in the rat

The purpose of the present study was to compare dexamethasone-induced glycogen increases in normal EDL and SOL muscles with that in free muscle grafts. Glycogen in mature EDL and SOL grafts in the rat equalled control concentrations irrespective of whether the graft was a nerve-intact (NI), nerve-crushed (NC), reimplanted, or cross-transplanted graft. The grafts also possessed the glycogen-regulatory mechanisms to respond to the glucocorticoid dexamethasone (DEX), which increases muscle glycogen. The increase in glycogen induced by DEX in the EDL and SOL grafts resembled that of the EDL and SOL muscles, respectively, whether the grafted muscle was originally an EDL or SOL. DEX induced an approximate twofold increase in glycogen concentration in control muscles and nerve-intact SOL grafts, and a smaller but significant increase in all other free grafts. Nerve crushing prior to grafting resulted in no significant change in muscle weight, glycogen concentration, or DEX-induced glycogen increase in these grafts. The data suggest that skeletal muscle grafts are qualitatively similar to normal muscles in terms of metabolic responsiveness to hormones. Leaving the nerve intact during grafting quantitatively enhances the graft's hormonal sensitivity but the technique of nerve crushing prior to grafting has no such effect.     

Distinct patterns of MMP-9 and MMP-2 activity in slow and fast twitch skeletal muscle regeneration in vivo

Skeletal muscles exhibit great plasticity and an ability to reconstruct in response to injury. However, the repair process is often inefficient and hindered by the development of fibrosis. We explored the possibility that during muscle repair, the different regeneration ability of the fast (extensor digitorum longus; EDL) and slow twitch (Soleus) muscles depends on the differential expression of metalloproteinases (MMP-9 and MMP-2) involved in the remodeling of the extracellular matrix. Our results show that MMP-9 and MMP-2 are present in the intact muscle and are up-regulated after crush-induced muscle injury. The expression and the activity of these two enzymes depend on the type of muscle and the phase of muscle regeneration. In the regenerating Soleus muscle, elevated levels of MMP-9 occurred during the myolysis and reconstruction phase. In contrast, regenerating EDL muscles exhibited decreased MMP-9 levels during myolysis and increased MMP-2 activity at the reconstruction phase. Moreover, satellite cells (mononuclear myoblasts) derived from Soleus and EDL muscles showed no differences in localization or activity of MMP-9 and MMP-2 during proliferation and differentiation in vitro. MMP-9 activity was present during all stages of myoblast differentiation, whereas MMP-2 activity reached its highest level during myoblast fusion. We conclude that MMPs are involved in muscle repair, and that fast and slow twitch muscles exhibit different patterns of MMP-9 and MMP-2 activity.     

Age modifies respiratory complex I and protein homeostasis in a muscle type‐specific manner

Changes in mitochondrial function with age vary between different muscle types, and mechanisms underlying this variation remain poorly defined. We examined whether the rate of mitochondrial protein turnover contributes to this variation. Using heavy label proteomics, we measured mitochondrial protein turnover and abundance in slow‐twitch soleus (SOL) and fast‐twitch extensor digitorum longus (EDL) from young and aged mice. We found that mitochondrial proteins were longer lived in EDL than SOL at both ages. Proteomic analyses revealed that age‐induced changes in protein abundance differed between EDL and SOL with the largest change being increased mitochondrial respiratory protein content in EDL. To determine how altered mitochondrial proteomics affect function, we measured respiratory capacity in permeabilized SOL and EDL. The increased mitochondrial protein content in aged EDL resulted in reduced complex I respiratory efficiency in addition to increased complex I‐derived H₂O₂ production. In contrast, SOL maintained mitochondrial quality, but demonstrated reduced respiratory capacity with age. Thus, the decline in mitochondrial quality with age in EDL was associated with slower protein turnover throughout life that may contribute to the greater decline in mitochondrial dysfunction in this muscle. Furthermore, mitochondrial‐targeted catalase protected respiratory function with age suggesting a causal role of oxidative stress. Our data clearly indicate divergent effects of age between different skeletal muscles on mitochondrial protein homeostasis and function with the greatest differences related to complex I. These results show the importance of tissue‐specific changes in the interaction between dysregulation of respiratory protein expression, oxidative stress, and mitochondrial function with age.     

Ultrastructural and gene-expression changes in the calcium regulation system of rat skeletal muscles under exhausting exercise

The expression of genes responsible for the synthesis of essential proteins regulating the calcium-ion balance and ultrastructural characteristics of fast-twitch (m. extensor digitorum longus, EDL) and slow-twitch (m. soleus, SOL) skeletal muscles under prolonged exercise were studied in an experimental model of forced-swimming rats. A day after the end of the exercise, no significant changes in any of the five investigated genes were revealed in the SOL. A few triad elements (T-tubules and cisternae of sarcoplasmic reticulum) were revealed. A small number of excitation-contraction coupling (ECC) structures in the control and a slight increase in their amount after exercises were noticed. Polymorphism and mitochondrial defects within SOL muscles indicate the importance of these structures in the regulation of calcium balance. In EDL muscles, adaptation mechanisms are aimed mainly at pumping Ca²⁺ ions to the sarcoplasmic reticulum, where the main calcium buffer is calsequestrin. Expression of SERCA1 gene increased by an order of magnitude, and that of CASQ1 increased by three times. Electron microscopy showed a major role of triads in the maintenance of calcium homeostasis in the EDL muscles, as well as a greater destruction of these muscles compared to SOL after exhausting exercise. The high level of triads and a possible activation of the CICR (calcium-induced calcium release) mechanism in fast-twitch muscles can cause damage to them during exhausting exercise. Adaptation of SOL muscles is associated with structural rearrangements of the mitochondrial apparatus, while adaptation of the EDL muscles is caused by calcium removal from the sarcoplasm with Ca-ATPase and its retention in the sarcoplasmic reticulum by calsequestrin.     

Removal of ovarian hormones from mature mice detrimentally affects muscle contractile function and myosin structural distribution.

The purposes of this study were to determine the effects of ovarian hormone removal on force-generating capacities and contractile proteins in soleus and extensor digitorum longus (EDL) muscles of mature female mice. Six-month-old female C57BL/6 mice were randomly assigned to either an ovariectomized (OVX; n = 13) or a sham-operated (sham; n = 13) group. In vitro contractile function of soleus and EDL muscles were determined 60 days postsurgery. Total protein and contractile protein contents were quantified, and electron paramagnetic resonance (EPR) spectroscopy was used to determine myosin structural distribution during contraction. OVX mice weighed 15% more than sham mice 60 days postsurgery, and soleus and EDL muscle masses were 19 and 15% greater in OVX mice, respectively (P < or = 0.032). Soleus and EDL muscles from OVX mice generated less maximal isometric force than did those from sham mice [soleus: 0.27 (SD 0.04) vs. 0.22 N.cm.mg(-1) (SD 0.04); EDL: 0.33 (SD 0.04) vs. 0.27 N.cm.mg(-1) (SD 0.04); P < or = 0.006]. Total and contractile protein contents of soleus and EDL muscles were not different between OVX and sham mice (P > or = 0.242), indicating that the quantity of contractile machinery was not affected by removing ovarian hormones. EPR spectroscopy showed that the fraction of strong-binding myosin during contraction was 15% lower in EDL muscles from OVX mice compared with shams [0.277 (SD 0.039) vs. 0.325 (SD 0.020); P = 0.004]. These results indicate that the loss of ovarian hormones has detrimental effects on skeletal muscle force-generating capacities that can be explained by altered actin-myosin interactions.     

Pax3 and Pax7 expression during myoblast differentiation in vitro and fast and slow muscle regeneration in vivo

In this report, we focused on Pax3 and Pax7 expression in vitro during myoblast differentiation and in vivo during skeletal muscle regeneration. We showed that Pax3 and Pax7 were present in EDL (extensor digitorum longus) and Soleus muscle derived cells. These cells express in vitro a similar level of Pax3 mRNA, however, differ in the levels of mRNA encoding Pax7. Analysis of Pax3 and Pax7 proteins showed that Soleus and EDL satellite cells differ in the level of Pax3/7 proteins and also in the number of Pax3/7 positive cells. Moreover, Pax3/7 expression was restricted to undifferentiated cells, and both proteins were absent at further stages of myoblast differentiation, indicating that Pax3 and Pax7 are down-regulated during myoblast differentiation. However, we noted that the population of undifferentiated Pax3/7 positive cells was constantly present in both in vitro cultured satellite cells of EDL and Soleus. In contrast, there was no significant difference in Pax3 and Pax7 during in vivo differentiation accompanying regeneration of EDL and Soleus muscle. We demonstrated that Pax3 and Pax7, both in vitro and in vivo, participated in the differentiation and regeneration events of muscle and detected differences in the Pax7 expression pattern during in vitro differentiation of myoblasts isolated from fast and slow muscles.     

Contraction-induced skeletal muscle FAT/CD36 trafficking and FA uptake is AMPK independent

The aim of this study was to investigate the molecular mechanisms regulating FA translocase CD36 (FAT/CD36) translocation and FA uptake in skeletal muscle during contractions. In one model, wild-type (WT) and AMP-dependent protein kinase kinase dead (AMPK KD) mice were exercised or extensor digitorum longus (EDL) and soleus (SOL) muscles were contracted, ex vivo. In separate studies, FAT/CD36 translocation and FA uptake in response to muscle contractions were investigated in the perfused rat hindlimb. Exercise induced a similar increase in skeletal muscle cell surface membrane FAT/CD36 content in WT (+34%) and AMPK KD (+37%) mice. In contrast, 5-aminoimidazole-4-carboxamide ribonucleoside only induced an increase in cell surface FAT/CD36 content in WT (+29%) mice. Furthermore, in the perfused rat hindlimb, muscle contraction induced a rapid (1 min, +15%) and sustained (10 min, +24%) FAT/CD36 relocation to cell surface membranes. The increase in cell surface FAT/CD36 protein content with muscle contractions was associated with increased FA uptake, both in EDL and SOL muscle from WT and AMPK KD mice and in the perfused rat hindlimb. This suggests that AMPK is not essential in regulation of FAT/CD36 translocation and FA uptake in skeletal muscle during contractions. However, AMPK could be important in regulation of FAT/CD36 distribution in other physiological situations.     

废用条件下大鼠和达乌尔黄鼠骨骼肌氧化应激和抗氧化防御能力与肌萎缩的比较研究

有鳞类(蛇和蜥蜴)具有较发达的嗅器和犁鼻器,对其不同种类嗅觉结构的认识有助于阐明爬行动物化学感觉的进化。本文采用组织学方法比较了草原沙蜥(Phrynocephalus frontalis)、荒漠沙蜥(P. przewalskii)、密点麻蜥(Eremias multiocellata)和秦岭滑蜥(Scincella tsinlingensis)的嗅器及犁鼻器。结果发现,草原沙蜥的鼻腔较为狭长,秦岭滑蜥呈梨形,其他两种蜥蜴的鼻腔略成圆形。秦岭滑蜥的嗅上皮最厚,其次是密点麻蜥和草原沙蜥,荒漠沙蜥最薄。犁鼻器主要由犁鼻腔、犁鼻感觉上皮、犁鼻神经及蘑菇体等组成,没有腺体。草原沙蜥和荒漠沙蜥的犁鼻腔较为宽阔,密点麻蜥和秦岭滑蜥的较窄。4种蜥蜴的犁鼻感觉上皮均较嗅上皮厚,蘑菇体向后逐渐缩小至消失,犁鼻感觉上皮成闭环状,包围犁鼻腔。密点麻蜥和秦岭滑蜥的犁鼻感觉上皮位于犁鼻器的背侧,蘑菇体位于腹侧;与此不同,两种沙蜥的犁鼻感觉上皮偏向于犁鼻器的腹内侧,蘑菇体位于背外侧。密点麻蜥的犁鼻感觉上皮最厚,其次为秦岭滑蜥,两种沙蜥最薄;秦岭滑蜥犁鼻感觉上皮的感觉细胞密度最高,其次是密点麻蜥,两种沙蜥最低。这些结果提示,密点麻蜥和秦岭滑蜥对嗅觉信号的依赖和投入较两种沙蜥多;4种蜥蜴犁鼻器的结构差异间接地佐证了有鳞类犁鼻器系统发生的特异性。     

超排处理对雌兔生殖器官中表皮生长因子表达的影响

本研究采用免疫荧光组织化学染色法和蛋白免疫印迹法比较研究了后肢去负荷大鼠(Rattus norvegicus)和冬眠不活动达乌尔黄鼠(Spermophilus dauricus)不同类型骨骼肌氧化应激水平和抗氧化防御能力及与肌萎缩之间的关系。结果显示,后肢去负荷14 d后,大鼠比目鱼肌和趾长伸肌肌萎缩程度显著升高,过氧化氢和丙二醛水平增加,Nrf2介导的抗氧化信号通路及下游抗氧化酶蛋白表达及活性显著下降;而冬眠不活动达乌尔黄鼠骨骼肌中肌萎缩指标并未出现变化,氧化应激水平维持夏季组水平,抗氧化酶和调控因子出现不同程度升高。研究表明,后肢去负荷导致非冬眠大鼠骨骼肌氧化应激水平升高,抗氧化防御能力减弱,可能是导致大鼠废用性肌萎缩的重要机制之一;而冬眠动物达乌尔黄鼠骨骼肌在自然废用状态下,抗氧化防御能力增强可能是防止自然冬眠不活动引起的废用性肌萎缩的重要机制。     

Intracellular Na+ and K+ shifts induced by contractile activities of rat skeletal muscles

The effects of direct and indirect electrical stimulation on intracellular potassium and sodium contents ([K]_i and [Na]_i, respectively) in rat soleus muscle (SOL) and extensor digitorum longus muscle (EDL) were investigated under in vivo conditions. The changes of [K]_i and [Na]_i contents in both muscles which were stimulated indirectly reached respective values at 30 min or 1 hr after the beginning of stimulation, whereas those of EDL stimulated with 60 Hz changed gradually through 2 hr stimulation. The shifts of [K]_i and [Na]_i in EDL occurred during the twitch contraction at considerably lower frequency stimulation (0.5–10 Hz), whereas those in SOL were observed during the tetanus contraction at high frequency stimulation (10–40 Hz). The difference of change in cationic shifts between EDL and SOL under low frequency stimulation was reduced by ouabain treatment, though the difference was still significant. When the muscles were indirectly stimulated 6000 times at 1,5,10 and 20 Hz, the cationic shifts in EDL were greater than those in SOL, extending over all frequencies. It was concluded that such a difference in ionic shift between contracting EDL and SOL may be primarily due to the difference in unidirectional ionic fluxes per stimulation and, secondly, to the difference in Na⁺-K⁺ pump activity.