Estimation of instantaneous moment arms of lower-leg muscles

Muscle moment arms at the human knee and ankle were estimated from muscle length changes measured as a function of joint flexion angle in cadaver specimens. Nearly all lower-leg muscles were studied: extensor digitorum longus, extensor hallucis longus, flexor digitorum longus, flexor hallucis longus, gastrocnemius lateralis, gastrocnemius medialis, peroneus brevis, peroneus longus, peroneus tertius, plantaris, soleus, tibialis anterior, and tibialis posterior. Noise in measured muscle length was filtered by means of quintic splines. Moment arms of the mm. gastrocnemii appear to be much more dependent on joint flexion angles than was generally assumed by other investigators. Some consequences for earlier analyses are mentioned.     

Distribution and developmental transition of phosphoglycerate mutase and creatine phosphokinase isozymes in rat muscles of different fiber-type composition

Phosphoglycerate mutase and creatine phosphokinase have in mammals three isozymes (types MM, MB and BB) with similar tissue distribution and developmental transition in muscle cells. To assess whether the phenotype and the developmental switch of these isozymes differ in the diverse types of muscle fibers, the enzymatic activities and the isozyme patterns, analyzed by cellulose acetate electrophoresis, have been determined in rat soleus, extensor digitorum longus and gastrocnemius muscles during postnatal development. Both phosphoglycerate mutase and creatine phosphokinase activity increased in the three muscles, the increase in extensor digitorum longus and gastrocnemius being higher than in soleus. For the two enzymes the increase in activity was due to the progressive increment of the muscle-specific forms. It is concluded that whereas phosphoglycerate mutase and creatine phosphokinase type-B subunits are present at similar levels in both type I and type II muscle fibers, phosphoglycerate mutase and creatine phosphokinase type-M subunits exhibit much higher levels in type II fibers.     

Effects of dexamethasone treatment on insulin-stimulated rates of glycolysis and glycogen synthesis in isolated incubated skeletal muscles of the rat.

1. Rats were treated with dexamethasone for 4 days before measurement of the rates of lactate formation [which is an index of hexose transport; see Challiss, Lozeman, Leighton & Newsholme (1986) Biochem. J. 233, 377-381] and glycogen synthesis in response to various concentrations of insulin in isolated incubated soleus and extensor digitorum longus muscle preparations. 2. The concentration of insulin required to stimulate these processes half-maximally in soleus and extensor digitorum longus muscles isolated from control rats was about 100 muunits/ml. 3. Dexamethasone increases the concentration of insulin required to stimulate glycolysis half-maximally in soleus and extensor digitorum longus preparations to 250 and 300 muunits/ml respectively. The respective insulin concentrations necessary to stimulate glycogen synthesis half-maximally were about 430 and 370 muunits/ml for soleus and extensor digitorum longus muscle preparations isolated from steroid-treated rats. 5. Dexamethasone treatment did not change the amount of insulin bound to soleus muscle.     

Enzymatic activities in slow and fast denervated old rat muscles

The activities of five enzymes have been studied quantitatively in denervated extensor digitorum longus, gastrocnemius and soleus muscles of 24-month-old rats. The results have been compared with those obtained from normal muscles of a similar age group of rats. Three weeks after denervation, the activity of hexokinase was increased in gastrocnemius and extensor digitorum longus. Phosphofructokinase, lactate dehydrogenase, malate dehydrogenase and 3-hydroxyacyl-CoA-dehydrogenase showed decreased activities. These results suggest that enzyme which represents glucose uptake increased its activity in fast muscles and that enzymes for anaerobic glycolysis, lactate fermentation, citric acid cycle and beta-oxidation had a decreased activity in slow and fast muscles.     

Insulin binding and 2-deoxy-D-glucose uptake in fast- and slow-twitch mouse skeletal muscle at 18 and 37 degrees C

Insulin binding, insulin degradation, and 2-deoxyglucose uptake were examined at 18 and 37 degrees C in soleus and extensor digitorum longus muscles of mice. Insulin binding and degradation were greater in the soleus than in the extensor digitorum longus at both temperatures (p less than 0.05). At 37 degrees C, binding was decreased in both muscles while percentage degradation was increased in comparison with 18 degrees C (p less than 0.05). Dose--response curves (percentage of binding at 4 nM of insulin) remained the same for both muscles at the two temperatures. Basal (no insulin) 2-deoxyglucose uptake was increased at 37 degrees C in the extensor digitorum longus but not the soleus. Insulin responsiveness in terms of the amount of 2-deoxyglucose taken up per femtomole of insulin bound was almost identical for the two muscles at 18 degrees C, whereas at 37 degrees C it was increased more in the soleus than in the extensor digitorum longus. The results indicate that in the presence of physiological concentrations of insulin (0.2-4 nM), insulin binding trends are minimally affected by increased temperature. In contrast, the ability of insulin to stimulate 2-deoxyglucose uptake varies between the two temperatures, and at the higher temperature between fast- and slow-twitch muscle.     

The effect of a growth promoting drug,clenbuterol, on fibre frequency and area in hind limb muscles from young male rats

The effect of dietary administration of clenbuterol on soleus and extensor digitorum longus muscles was studied after 4 and 21 days. Both muscles showed an increase in wet weight with no significant change in total fibre number. After 4 days fibre cross-sectional areas were increased in soleus, but not in extensor digitorum longus, and after 21 days there was a change in fibre frequencies in extensor digitorum longus but not soleus muscles.     

Histochemical fiber type distribution and epinephrine sensitivity in normal and cross-transplanted rat muscles

The metabolic integrity of fully regenerated transplants was investigated by measuring induced changes in glycogen concentration. The extensor digitorum longus and the soleus muscles were cross transplanted: the extensor digitorum longus into the soleus muscle bed (SOLT) and the soleus muscle into the extensor digitorum longus bed (EDLT). The histochemical fiber type distribution of the regenerated muscles was determined and was found to transform in cross-transplanted EDLT and SOLT. After transplantation and regeneration, both muscles had initially low glycogen concentrations. However, the EDLT glycogen concentration was not significantly different from that of the contralateral extensor digitorum longus control muscle after 60 days. In the SOLT, glycogen gradually increased but remained less than in the contralateral soleus control muscle. SOLT and control soleus muscles responded with a significant glycogen depletion to an epinephrine dose two orders of magnitude less than the lowest dose affecting glycogen levels in EDLT and extensor digitorum longus muscles. These results indicate that transplanted muscles are capable of regenerating normal glycogenolytic responses and that the sensitivity of the response observed depends on the site of transplantation and is related to the type of innervation and histochemical fiber type.     

八眉猪、长白猪及长×八杂交猪肌肉组织中FoxO1基因的表达

分别取6月龄八眉、长白和 (长×八)杂交猪后腿部比目鱼肌、腓肠肌和趾长伸肌, 提取总RNA, 根据人、黑猩猩及大鼠等物种FoxO1基因同源序列设计并合成引物, 以猪b-actin 基因作为内参, 优化反应条件和体系, RT-PCR 单管扩增猪FoxO1基因, 检测八眉、长白和长×八杂交猪不同类型骨骼肌中FoxO1基因mRNA的表达差异。结果表明: 在不同经济类型猪群和不同类型骨骼肌中FoxO1基因mRNA的表达丰度不同, 即在八眉 猪骨骼肌中的表达普遍高于长白猪 (P<0.01), 在杂交组合 (长×八)骨骼肌中的表达也高于长白猪 (P<0.01); 同时在以Ⅰ型纤维为主的比目鱼肌中表达丰度最低(P<0.01), 在以Ⅱb型纤维为主的趾长伸肌中表达丰度最高(P<0.01)。结果提示, FoxO1基因的表达与Ⅰ型肌纤维的含量成反比; 不同经济类型猪品种骨骼肌的发育与FoxO1基因的调控有关。     

Regulation of protein metabolism by a physiological concentration of insulin in mouse soleus and extensor digitorum longus muscles. Effects of starvation and scald injury.

1. Although high concentrations of insulin affect both synthesis and degradation of skeletal-muscle protein, it is not known to what extent these effects occur with physiological concentrations. The effects of a physiological concentration of insulin (100 mu units/ml) on muscle protein synthesis, measured with [3H]tyrosine, and on muscle protein degradation, measured by tyrosine release in the presence of cycloheximide, were studied in mouse soleus and extensor digitorum longus muscles in vitro. 2. Insulin significantly stimualated protein synthesis in both muscles, but an inhibition of degradation was seen only in the extensor digitorum longus. 3. Starvation for 24 h decreased the rate of protein synthesis and increased the rate of breakdown in the extensor digitorum longus. Sensitivity to insulin-stimulation of proteins synthesis in the soleus was increased by starvation. 4. ;a 20%-surface-area full-skin-thickness dorsal scald injury produced a fall in total protein content in soleus and extensor digitorum muscles, maximal on the third day after injury. Soleus muscles 2 days after injury showed an impairment of protein synthesis; degradation was unaffected and neither synthesis nor degradation in vitro was significantly affected in the extensor digitorum longus. 5. The advantages and limitations of studies of protein metabolism in vitro are discussed.     

A rat model of progressive isometric strength training

This study presents an isometric model of strength resistance training in rats. Seven rats were trained for five weeks with increasing load, once a day for six days per week while seven rats served as control group. Mechanical strength of the hindlimb muscle group was measured on anaesthetised rats with a force transducer linked to the Achilles tendon after electrical stimulation of the sciatic nerve. Training resulted in a 74 +/- 2% strength gain in experimental (E) vs control (C) rats and in a reduction of fatigability with no change in gastrocnemius, soleus and extensor digitorum longus weights. The fibres composition of the gastrocnemius showed a 50% increase of IIA fibres and a 17% fall of IIB fibres. Consequently, this new model of isometric training is suitable for physiological studies.     

Postnatal development of thiamine metabolism in rat skeletal muscle.

1. The activities of 2-oxoglutarate dehydrogenase, transketolase, thiamine pyrophosphokinase and thiamine triphosphatase and the concentrations of thiamine phosphates were almost the same between rat extensor digitorum longus and soleus muscles at 2 weeks of age. 2. These enzyme activities changed after 3 weeks of age in a different way depending on the muscle phenotype. 3. Thiamine diphosphate level and the activity of 2-oxoglutarate dehydrogenase increased only in soleus muscle and thiamine triphosphate level increased only in extensor digitorum longus during development.     

Time courses of the responses of pyruvate dehydrogenase activities to short-term starvation in diaphragm and selected skeletal muscles of the rat.

In the fed state, the percentages of the pyruvate dehydrogenase complex (PDH) in the active form (PDHa) in diaphragm and a selection of skeletal muscles (adductor longus, soleus, extensor digitorum longus, tibialis anterior, gastrocnemius) ranged from 8% (soleus) to 38% (gastrocnemius). Major decreases in PDHa activities in all of these muscles were observed after 15 h of starvation, by which time activities were less than 40% of the fed values. In general, the response to starvation was observed more rapidly in muscles of high oxidative capacity. The patterns of changes in skeletal-muscle PDH activities during the fed-to-starved transition are discussed in relation to changes in lipid-fuel supply and oxidation.     

The effects of cutting or of stretching skeletal muscle in vitro on the rates of protein synthesis and degradation.

Rates of protein synthesis were significantly lower in the cut soleus and extensor digitorum longus muscles than in their uncut counterparts. Rates of protein degradation were significantly higher in cut soleus muscles, but not in cut extensor digitorum longus muscles as compared with their uncut controls. Concentrations of ATP and phosphocreatine were significantly lower in cut soleus and extensor digitorum longus muscles after incubation in vitro in contrast with respective control uncut muscles. These data indicate that cutting of muscle fibres alters rates of protein synthesis and degradation, in addition to altering concentrations of high-energy phosphates. Since these findings stressed the importance of using intact muscles to study protein metabolism, additional studies were made on intact muscles in vitro. Stretched soleus muscles had higher concentrations of high-energy phosphates at the end of an incubation period than did unstretched muscles. However, the length of the soleus, extensor digitorum longus and diaphragm muscles during incubation did not affect rates of protein degradation.U     

Inhibition of carbonic anhydrases in type I muscle fibers influences contractility

We tested the effects of inhibiting the carbonic anhydrase activity of rat soleus and extensor digitorum longus muscles on the isometric contractile properties and the resistance to fatigue. SOL and EDL muscles from female rats were incubated in vitro in the presence of methazolamide, a specific inhibitor of carbonic anhydrase, before determining their contractile properties. Methazolamide had no effects on the contractile properties of the soleus muscle (10(-5) or 10(-3) M) and extensor digitorum longus (10(-3) M), except for the half-relaxation time of the soleus muscle which increased significantly. Values for half-relaxation time were significantly increased with both concentrations of the inhibitor. Muscles were then submitted to a fatigue protocol lasting 30 min. During the fatigue test, no significant difference was observed between control and 10(-5) M methazolamide soleus muscles. In presence of 10(-3) M methazolamide however, the soleus muscle showed a significantly increased resistance to fatigue compared with control preparations. No significant effect was observed with the extensor digitorum longus muscle exposed to 10(-3) M methazolamide. Results are discussed in terms of the presence of two different isoforms of carbonic anhydrase that may be associated with calcium uptake and energy metabolic processes, respectively.     

Potentiation of the halothane-cooling contractures of mammalian muscles by denervation

Denervation potentiated the cooling-induced contractures and the halothane-cooling contractures of isolated extensor digitorum longus and soleus muscles of the mouse. These effects were more striking in extensor digitorum longus than in soleus muscles. Significant increases in the peak amplitudes of the halothane-cooling contractures of both muscles and of the cooling contractures of soleus muscle were observed within 2 and 7 days of denervation. The potentiation of the contractures persisted for 90 days, the period of this study. Denervation (greater than 2 days) endowed extensor digitorum longus with the ability to generate cooling contractures in the absence of halothane. The rate of tension development of cooling-induced contractures in the absence or presence of halothane was significantly greater in denervated (2-90 days) than in innervated muscles. Denervation also reduced the effectiveness of procaine in inhibiting the halothane-cooling contractures. It is proposed that the potentiation of cooling-induced contractures in denervated muscles results primarily from an increase in the rate of efflux and in the quantity of Ca2+ released from the sarcoplasmic reticulum, upon cooling and (or) when challenged with halothane.     

Life-long calorie restriction in Fischer 344 rats attenuates age-related loss in skeletal muscle-specific force and reduces extracellular space.

The decline in muscle function is associated with an age-related decrease in muscle mass and an age-related decline in strength. However, decreased strength is not solely due to decreased muscle mass. The age-related decline in muscle-specific force (force/muscle cross-sectional area), a measure of intrinsic muscle function, also contributes to age-related strength decline, and the mechanisms by which this occurs are only partially known. Moreover, changes in the extracellular space could have a profound effect on skeletal muscle function. Life-long calorie restriction in rodents has shown to be a powerful anti-aging intervention. In this study, we examine whether calorie restriction is able to attenuate the loss of muscle function and elevations in extracellular space associated with aging. We hypothesize that calorie restriction attenuates the age-associated decline in specific force and increases in extracellular space. Measurements of in vitro contractile properties of the extensor digitorum longus (type II) and soleus (type I) muscles from 12-mo and 26- to 28-mo-old ad libitum-fed, as well as 27- to 28-mo-old life-long calorie-restricted male Fischer 344 rats, were performed. We found that calorie restriction attenuated the age-associated decline in muscle mass-to-body mass ratio (mg/g) and strength-to-body mass ratio (N/kg) in the extensor digitorum longus muscle (P < 0.05) but not in the soleus muscle (P > 0.05). Importantly, muscle-specific force (N/cm2) in the extensor digitorum longus, but not in the soleus muscle, of the old calorie-restricted rats was equal to that of the young 12-mo-old animals. Moreover, the age-associated increase in extracellular space was reduced in the fast-twitch extensor digitorum longus muscle (P < 0.05) but not in the soleus muscle with calorie restriction. We also found a significant correlation between the extracellular space and the muscle-specific force in the extensor digitorum longus (r = -0.58; P < 0.05) but not in the soleus muscle (r = -0.38; P > 0.05). Hence, this study shows a loss of muscle function with age and suggests that long-term calorie restriction is an effective intervention against the loss of muscle function with age.     

Denervated muscle fibers explain the deficit in specific force following reinnervation of the rat extensor digitorum longus muscle

The authors tested the hypothesis that, after denervation and reinnervation of skeletal muscle, observed deficits in specific force can be completely attributed to the presence of denervated muscle fibers. The peroneal nerve innervating the extensor digitorum longus muscle in rats was sectioned and the distal stump was coapted to the proximal stump, allowing either a large number of motor axons (nonreduced, n = 12) or a drastically reduced number of axons access to the distal nerve stump (drastically reduced, n = 18). A control group of rats underwent exposure of the peroneal nerve, without transection, followed by wound closure (control, n = 9). Four months after the operation, the maximum tetanic isometric force (Fo) of the extensor digitorum longus muscle was measured in situ and the specific force (sFo) was calculated. Cross-sections of the muscles were labeled for neural cell adhesion molecule (NCAM) protein to distinguish between innervated and denervated muscle fibers. Compared with extensor digitorum longus muscles from rats in the control (295 +/- 11 kN/m2) and nonreduced (276 +/- 12 kN/m2) groups, sFo of the extensor digitorum longus muscles from animals in the drastically reduced group was decreased (227 +/- 15 kN/m2, p < 0.05). The percentage of denervated muscle fibers in the extensor digitorum longus muscles from animals in the drastically reduced group (18 +/- 3 percent) was significantly higher than in the control (3 +/- 1 percent) group, but not compared with the nonreduced (9 +/- 2 percent) group. After exclusion of the denervated fibers, sFo did not differ between extensor digitorum longus muscles from animals in the drastically reduced (270 +/- 20 kN/m2), nonreduced (301 +/- 13 kN/m2), or control (303 +/- 10 kN/m2) groups. The authors conclude that, under circumstances of denervation and rapid reinnervation, the decrease in sFo of muscle can be attributed to the presence of denervated muscle fibers.     

Blood flow and glycogen use in hypertrophied rat muscles during exercise

Previous findings suggest that skeletal muscle that has enlarged as a result of removal of synergistic muscles has a similar metabolic capacity and improved resistance to fatigue compared with normal muscle. The purpose of the present study was to follow blood flow and glycogen loss patterns in hypertrophied rat plantaris plantaris and soleus muscles during treadmill exercise to provide information on the adequacy of perfusion of the muscles during in vivo exercise. Thirty days following surgical removal of gastrocnemius muscle, blood flows (determined with radiolabeled microspheres) and glycogen concentrations were determined in all of the ankle extensor muscles of experimental and sham-operated control rats during preexercise and after 5-6 min of treadmill exercise at 15 m/min. There were no differences (P greater than 0.05) in blood flows per unit mass or glycogen concentrations between control and hypertrophied plantaris or soleus muscles at either time, although both muscles were larger (P less than 0.05) in the experimental group (plantaris: 95%; soleus: 40%). None of the other secondary ankle extensor muscles (tibialis posterior, flexor digitorum longus or flexor hallicus longus) hypertrophied in response to removal of gastrocnemius. These results provide indirect evidence that O2 delivery in the enlarged muscles is not compromised during low-intensity treadmill exercise due to limited perfusion.     

Difference in thiamine metabolism between extensor digitorum longus and soleus muscles

1. Thiamine diphosphate level was higher in soleus muscle than in extensor digitorum longus muscle in various animals, whereas thiamine triphosphate level was less in the former muscle than in the latter except for mouse. 2. 2-Oxoglutarate dehydrogenase, transketolase and thiamine pyrophosphokinase activities were higher in soleus muscle than in extensor digitorum longus in rat and guinea pig. 3. The differences between rat two muscle phenotypes in thiamine diphosphate, but not thiamine triphosphate, level and the thiamine-related enzyme activities disappeared after denervation. 4. Tenotomy had little effect on thiamine phosphate levels and the thiamine-related enzyme activities in rat skeletal muscles.