大鼠与家兔生后各年龄阶段跖肌纤维的比较

应用建立在肌球蛋白重链异构体基础上的标准肌动球蛋白ATP酶和琥珀酸脱氢酶组织化学方法,分析大鼠和家兔出生后发育各年龄阶段跖肌纤维型分布。在生后2周至24周龄的大鼠和家兔Ⅰ、ⅡX型肌纤维百分比例减少,而ⅡA、ⅡB型纤维则增加。进行大量单肌纤维的组织化学特征的比较和相关性探讨。结果显示动物平均体重与跖肌的平均湿重随生后发育逐渐增加,Ⅰ、ⅡX、ⅡA及ⅡB型纤维均在生后各年龄组的全部肌肉内被发现,但出生后2日龄组是个例外。在生后发育期间,雄性大鼠和家兔ⅡB型纤维的平均肌纤维型构成要大于雌性大鼠和家兔,而雄性大鼠和家兔Ⅰ、ⅡX、ⅡA型三种氧化组织化学分类的肌纤维型构成均小于雌性大鼠和家兔。大鼠Ⅰ、ⅡX、ⅡA和ⅡB型纤维的平均横切面积显然要比家兔的同类型肌纤维要小。在大鼠和家兔可见明显的性别差异。大鼠和家兔的ⅡX型纤维横切面积是最小的,Ⅰ、ⅡA型纤维呈中等大小,ⅡB型纤维最大。该重要的测试有助于我们深入研究啮齿类动物快肌纤维生理特征的适应。     

The claw closer muscle of Neohelice granulata (Grapsoidea,Varunidae): a morphological and histochemical study

Longo, M.V., Goldemberg, A.L. and Díaz, A.O. 2011. The claw closer muscle of Neohelice granulata (Grapsoidea, Varunidae): a morphological and histochemical study. —Acta Zoologica (Stockholm) 92 : 126–133. The claw closer muscle of Neohelice granulata was studied according to histological, histochemical, and morphometrical criteria. Adult male crabs in intermoult stage were collected from Mar Chiquita Lagoon (Buenos Aires, Argentina). Muscle fibers show evident striations and oval‐elongated nuclei with loose chromatin. The loose connective tissue among muscle fibers consists of cells and fibers embedded in an amorphous substance. Muscle histochemistry reveals two slow fiber types: ‘A’ and ‘B’. Prevailing A fibers are larger, and they usually show, with respect to B type, a weaker reaction to whole techniques. Fibers with short (SS), intermediate (IS), and long sarcomeres (LS) appear in the claw closer muscle, being the LS fibers predominant. Concluding, the histochemical and morphometrical characteristics of the claw closer muscle fibers of N. granulata are indicative of slow fibers. The slow A type (low resistant to fatigue) prevails.     

高强度间歇训练：调节骨骼肌质量及功能的新手段

近年来,高强度间歇训练（high-intensity interval training,HIIT）被认为是一种调节骨骼肌质量及功能的运动方式,但其具体作用和机制以及运动和检测中需要注意的问题尚不明确。因此,梳理HIIT与骨骼肌质量及功能的关系显得尤为重要。本文综述HIIT上调骨骼肌蛋白质合成速率和下调萎缩速率、引发肌肉重塑和调节肌纤维类型、促进血管生成和血流灌注、介导骨骼肌线粒体含量上调和功能改善、增加肌肉力量和与膳食补充的协同作用等影响骨骼肌质量及功能的研究进展,为HIIT预防和改善肌肉丢失和功能下降提供理论依据和应用策略。     

Protein synthesis in skeletal muscle measured at different times during a 24 hour period

Six groups of 5 male rats (starting body weight 109 g) were allowed free access to a conventional rat diet. At 4 hourly intervals, starting at 10.00 h muscle protein synthesis was measured. By relating the weights of the gastrocnemius and soleus muscles to the initial body weights of the animals (i.e., at 09.30, day 1), a linear increase in muscle weight throughout the day was demonstrated. The fractional rate of muscle protein synthesis varied from 16.8% per day to 20.3% per day in gastrocnemius muscle and from 17.9% per day and 22.1% per day in the soleus. It was calculated that the maximum error incurred in estimating daily muscle protein synthesis by extrapolation of the value at any one time was 6% in gastrocnemius and 9% in soleus. It is concluded that calculations of the average rate of muscle protein degradation based on the difference between the rates of synthesis and deposition are generally valid in rats allowed free access to an adequate diet.     

Histochemical demonstration of enzymatic heterogeneity within the mesocoxal and metacoxal muscles of Periplaneta americana

Enzymatic activity in the mesocoxal and metacoxal muscles of the cockroach, Periplaneta americana, has been characterized using histochemical techniques. Our interpretation of the histochemical stains for myosin-ATPase (pre-incubated at pH 9.4, 10.4 and 4.3). NADH reductase, succinic dehydrogenase (SDH), and lactic dehydrogenase (LDH) has enabled us to classify fibres within these muscles according to established fibre typing strategies. The results reaffirm the biochemical heterogeneity reported for the mesocoxal muscles and allow us to confirm the expected heterogenity in the homologous metacoxal muscles. These techniques have proven to be an effective tool for assessing the biochemical properties of muscle fibres.     

Direct measurement of intracellular free magnesium in frog skeletal muscle using magnesium-selective microelectrodes

Mg²⁺-selective microelectrodes have been used to measure the intracellular free Mg²⁺ concentration in frog skeletal muscle fibers. Glass capillaries with a tip diameter of less than 0.4 μm were backfilled with the Mg²⁺ sensor, ETH 1117. In the absence of interfering ions, they gave Nernstian responses between 1 and 10 mM free Mg²⁺. In the presence of an ionic environment resembling the myoplasm, the microelectrode response was sub Nernstian (18–24 mV) but still useful. The electrodes were calibrated before and after muscle-fiber impalements. In quiescent fibers from sartorius muscle (Rana pipiens), with resting membrane potentials not less than ?82 mV, the intracellular free Mg²⁺ concentration was 3.8±0.41 (S.E.) mM (n=58) at 22°C. No significant change in the intracellular free Mg²⁺ was observed following extensive (approx. 6 h) incubation in Mg²⁺-free media. Increasing the external concentration of magnesium from 4 to 20 mM (approx. 15 min) produced a slow and small enhancement (1.8 mM) of [Mg²⁺]_i, which was fully reverted when the divalent cation was removed from the bathing solution. No change in ionic magnesium resting concentration was observed when the muscle fibers were treated either with caffeine 3 mM or with Na⁺-free solutions. In depolarized muscle fibers (?23±2.7 mV) treated with 100 mM K⁺, the myoplasmic [Mg²⁺] was 3.7±0.45 (S.E.) mM, n=6, immediately after the spontaneous relaxation of the contracture. Similar determinations in muscle fibers during stimulation at low frequency (5 Hz), and after fatigue development, showed no changes in the concentration of free cytosolic Mg²⁺. These results point out that [Mg²⁺]_i is not modified under these three different experimental conditions.     

The evolution of skeletal muscle performance: gene duplication and divergence of human sarcomeric α‐actinins

In humans, there are two skeletal muscle α‐actinins, encoded by ACTN2 and ACTN3, and the ACTN3 genotype is associated with human athletic performance. Remarkably, approximately 1 billion people worldwide are deficient in α‐actinin‐3 due to the common ACTN3 R577X polymorphism. The α‐actinins are an ancient family of actin‐binding proteins with structural, signalling and metabolic functions. The skeletal muscle α‐actinins diverged ～250–300 million years ago, and ACTN3 has since developed restricted expression in fast muscle fibres. Despite ACTN2 and ACTN3 retaining considerable sequence similarity, it is likely that following duplication there was a divergence in function explaining why α‐actinin‐2 cannot completely compensate for the absence of α‐actinin‐3. This paper focuses on the role of skeletal muscle α‐actinins, and how possible changes in functions between these duplicates fit in the context of gene duplication paradigms.     

Skeletal muscle design to meet functional demands

Skeletal muscles are length- and velocity-sensitive force producers, constructed of a vast array of sarcomeres. Muscles come in a variety of sizes and shapes to accomplish a wide variety of tasks. How does muscle design match task performance? In this review, we outline muscle''s basic properties and strategies that are used to produce movement. Several examples are provided, primarily for human muscles, in which skeletal muscle architecture and moment arms are tailored to a particular performance requirement. In addition, the concept that muscles may have a preferred sarcomere length operating range is also introduced. Taken together, the case is made that muscles can be fine-tuned to perform specific tasks that require actuators with a wide range of properties.     

What drives activation-dependent shifts in the force–length curve?

Skeletal muscles are rarely recruited maximally during movement. However, much of our understanding of muscle properties is based on studies using maximal activation. The effect of activation level on skeletal muscle properties remains poorly understood. Muscle optimum length increases with decreased activation; however, the mechanism responsible is unclear. Here, we attempted to determine whether length-dependent calcium effects, or the effect of absolute force underpin this shift. Fixed-end contractions were performed in frog plantaris muscles at a range of lengths using maximal tetanic (high force, high calcium), submaximal tetanic (low force, high calcium) and twitch (low force, low calcium) stimulation conditions. Peak force and optimum length were determined in each condition. Optimum length increased with decreasing peak force, irrespective of stimulation condition. Assuming calcium concentration varied as predicted, this suggests that absolute force, rather than calcium concentration, underpins the effect of activation level on optimum length. We suggest that the effect of absolute force is due to the varying effect of the internal mechanics of the muscle at different activation levels. These findings have implications for our understanding of in vivo muscle function and suggest that mechanical interactions within muscle may be important determinants of force at lower levels of activation.     

Alterations in intrinsic mitochondrial function with aging are fiber type-specific and do not explain differential atrophy between muscles

To determine whether mitochondrial dysfunction is causally related to muscle atrophy with aging, we examined respiratory capacity, H(2) O(2) emission, and function of the mitochondrial permeability transition pore (mPTP) in permeabilized myofibers prepared from four rat muscles that span a range of fiber type and degree of age-related atrophy. Muscle atrophy with aging was greatest in fast-twitch gastrocnemius (Gas) muscle (-38%), intermediate in both the fast-twitch extensor digitorum longus (EDL) and slow-twitch soleus (Sol) muscles (-21%), and non-existent in adductor longus (AL) muscle (+47%). In contrast, indices of mitochondrial dysfunction did not correspond to this differential degree of atrophy. Specifically, despite higher protein expression for oxidative phosphorylation (oxphos) system in fast Gas and EDL, state III respiratory capacity per myofiber wet weight was unchanged with aging, whereas the slow Sol showed proportional decreases in oxphos protein, citrate synthase activity, and state III respiration. Free radical leak (H(2) O(2) emission per O(2) flux) under state III respiration was higher with aging in the fast Gas, whereas state II free radical leak was higher in the slow AL. Only the fast muscles had impaired mPTP function with aging, with lower mitochondrial calcium retention capacity in EDL and shorter time to mPTP opening in Gas and EDL. Collectively, our results underscore that the age-related changes in muscle mitochondrial function depend largely upon fiber type and are unrelated to the severity of muscle atrophy, suggesting that intrinsic changes in mitochondrial function are unlikely to be causally involved in aging muscle atrophy.     

人骨骼肌M蛋白的提取与纯化

依据Ｔｒｉｎｉｃｋ－Ｅｐｐｅｎｂｅｒｇｅｒ对鸡骨骼肌Ｍ蛋白的提取方法,由人骨骼肌中得到的Ｍ蛋白粗提物除含分子量为１６５０００的Ｍ蛋白外,还含有分子量为１８５０００和１４００００（Ｃ成分）的两组分。由于在粗提物中未发现分子量为９００００的磷酸化酶,我们将最终纯化步骤中的亲和层析改为制备电泳,同样获得了纯化的Ｍ蛋白。