Effect of diffusion distance on measurement of rat skeletal muscle glucose transport in vitro

The relationships between muscle size, diffusion distance, and glucose uptake were studied using the Type II b epitrochlearis (13 ± 1 mg intact), Type I soleus (25± 1 mg), and mixed Type II a/II b extensor digitorum longus (25 ± 1 mg) from 60–70 g rats. Using intact muscles, the relative rates of 3-O-methyl-glucose uptake in response to 2 mUml^-1 insulin were soleus = epitrochlearis > extensor digitorum longus, a finding inconsistent with the fibre-type compositions and the relative GLUT-4 protein levels (soleus > extensor digitorum longus > epitrochlearis). To test whether these results were influenced by substrate diffusion limitations in the tubular muscles, soleus and extensor digitorum longus were split longitudinally from tendon to tendon into strips of comparable size (13 ± 1 mg) to the epitrochlearis. Insulin-stimulated rates of 3-O-methyl-glucose uptake were significantly enhanced in the split soleus (+120%) and split extensor digitorum longus (+200%), but not in the epitrochlearis, with the relative rates being soleus > extensor digitorum longus > epitrochlearis. Diffusion distances of the split soleus and extensor digitorum longus, as reflected by [¹⁴C]mannitol space equilibration time, were markedly enhanced (by at least 50%) relative to the intact muscles, and were comparable to that of the epitrochlearis. These results indicate that when muscles of different size and/or shape are used for in vitro measurement of glucose transport, the muscle preparations used must have similar diffusion distances for physiologically meaningful comparisons to be made.     

尾部悬吊对大鼠比目鱼肌梭内外肌纤维SDH活性的影响

:【目的】研究尾部悬吊对大鼠比目鱼肌梭内、外肌纤维琥珀酸脱氢酶 (succinicdehydrogenase,SDH)活性的影响 ,旨在探讨失重或模拟失重状态下肌梭的代谢和功能变化。【方法】用尾部悬吊法模拟失重 ,雌性Sprague Dawley大鼠按体质量配对原则 ,随机分为尾部悬吊 3、7、14、30d组及同步饲养的对照组。以氯化硝基四氮唑蓝盐 (nitrobluetetrazolium ,Nitro BT)法检测比目鱼肌梭内、外肌纤维SDH的活性。【结果】尾部悬吊导致Ⅰ型肌纤维的构成比减少 ,Ⅱ型肌纤维各亚型的构成比增加 ,以Ⅱb型增加最显著。尾部悬吊 3、7、14、30d组的Ⅰ型肌纤维构成比分别为 87.92 % ,84.0 0 % (P <0 .0 5 ) ,6 9.90 %(P <0 .0 1) ,6 7.90 % (P <0 .0 1) ;Ⅱb型肌纤维的构成比分别是 3 .75 % ,5 .6 3% (P <0 .0 5 ) ,15 .35 % (P <0 .0 1) ,18.33%(P <0 .0 1)。梭内肌纤维SDH活性增强 ,核袋 1纤维SDH染色由阳性转变为强阳性 ,核袋 2纤维由阴性转变为中等以上阳性 ,核链纤维由仅有一条呈弱阳性转变为均呈强阳性。【结论】模拟失重导致梭内、外肌纤维代谢改变 ,骨骼肌发生肌纤维类型转换 ,肌梭的功能活动可能受影响。     

Comparison of metabolic adaptations between endurance‐ and sprint‐trained athletes after an exhaustive exercise in two different calf muscles using a multi‐slice 31P‐MR spectroscopic sequence

Measurements of exercise‐induced metabolic changes, such as oxygen consumption, carbon dioxide exhalation or lactate concentration, are important indicators for assessing the current performance level of athletes in training science. With exercise‐limiting metabolic processes occurring in loaded muscles, ³¹P‐MRS represents a particularly powerful modality to identify and analyze corresponding training‐induced alterations. Against this background, the current study aimed to analyze metabolic adaptations after an exhaustive exercise in two calf muscles (m. soleus – SOL – and m. gastrocnemius medialis – GM) of sprinters and endurance athletes by using localized dynamic ³¹P‐MRS. In addition, the respiratory parameters VO₂ and VCO₂, as well as blood lactate concentrations, were monitored simultaneously to assess the effects of local metabolic adjustments in the loaded muscles on global physiological parameters. Besides noting obvious differences between the SOL and the GM muscles, we were also able to identify distinct physiological strategies in dealing with the exhaustive exercise by recruiting two athlete groups with opposing metabolic profiles. Endurance athletes tended to use the aerobic pathway in the metabolism of glucose, whereas sprinters produced a significantly higher peak concentration of lactate. These global findings go along with locally measured differences, especially in the main performer GM, with sprinters revealing a higher degree of acidification at the end of exercise (pH 6.29 ± 0.20 vs. 6.57 ± 0.21). Endurance athletes were able to partially recover their PCr stores during the exhaustive exercise and seemed to distribute their metabolic activity more consistently over both investigated muscles. In contrast, sprinters mainly stressed Type II muscle fibers, which corresponds more to their training orientation preferring the glycolytic energy supply pathway. In conclusion, we were able to analyze the relation between specific local metabolic processes in loaded muscles and typical global adaptation parameters, conventionally used to monitor the training status of athletes, in two cohorts with different sports orientations.     

L-Cysteine Increases Glucose Uptake in Mouse Soleus Muscle and SH-SY5Y Cells

Previous investigation demonstrated the potential of L-cysteine (L-Cys) at high concentrations to cause hypoglycemia in mice totally deprived of insulin. For further elucidation of the glucose-lowering mechanism, glucose uptake and quantity of glucose transporters (GLUTs 3 and 4) in mouse soleus muscle and C2C12 muscle cells, as well as in human SH-SY5Y neuroblastoma cells, were investigated. A marked enhancement of glucose uptake was demonstrated, peaking at 5.0 mM L-Cys in soleus muscle (P < 0.05) and SH-SY5Y cells (P < 0.001), respectively. In contrast, glucose uptake was not affected in the C2C12 muscle cells. Kinetic analysis of the SH-SY5Y glucose uptake showed a 2.5-fold increase in maximum transport velocity compared with controls (P < 0.001). In addition, both GLUT3 and GLUT4 levels were increased following exposure to L-Cys. Our findings point to a possible hypoglycemic effect of L-Cys.     

Evidence for treatment of muscular vein thrombosis in orthopaedic patients

Background

Does below-knee symptomatic muscular (gastrocnemius or soleus) vein thrombosis (MVT) warrant investigation and treatment in post-operative orthopaedic patients? We performed a literature search and evaluated the evidence looking for guidance regarding this question.

Materials and methods

We performed a literature search with the use of PubMed, Medline and Google Scholar from 1950 to September 2011. Search terms included “muscular vein thrombosis” (MVT) and “isolated gastrocnemius or soleus vein thrombosis” (IGSVT). We reviewed the eight level II studies relevant to our search, only one of which was in a specific orthopaedic population.

Results

Studies looking at the rates of progression of isolated MVT have shown conflicting results. There is also a lack of consensus between studies that compare progression amongst groups with or without anticoagulant treatment. The majority of the studies do not distinguish between medical, surgical or orthopaedic patients.

Conclusions

We cannot confidently recommend commencement of anticoagulation treatment upon identification of MVT in post-operative orthopaedic patients. We can only suggest that, once MVT is diagnosed, the patient should undergo serial ultrasound scan (USS) duplex scans, and if propagation is identified, then treatment may be deemed beneficial.Level of evidence: III (review of non-randomized controlled cohort/follow-up studies).     

氯化琥珀胆碱对大鼠比目鱼肌离体单一肌梭传入放电的影响

目的 探讨不同浓度氯化琥珀胆碱(suxamethonium chloride,Sch)对大鼠比目鱼肌离体单一肌梭传入放电的影响。方法 采用空气隔绝法记录大鼠比目鱼肌离体单一肌梭传入放电,分别给予25 mg/L、50mg/L、75 mg/L、100 mg/L、125 mg/L Sch灌流后,观察大鼠比目鱼肌离体单一肌梭传入放电的变化。结果1)给予25 mg/L Sch灌流后,大鼠比目鱼肌离体单一肌梭传入放电较灌流前无明显变化;2)分别给予50 mg/L、75 mg/L Sch灌流后,肌梭传入放电较灌流前明显增多(P0.01);3)给予100 mg/L Sch灌流后,肌梭传入放电较灌流前无明显变化;4)给予125 mg/L Sch灌流后,肌梭传入放电较灌流前明显减少(P0.05)。结论 一定浓度的氯化琥珀胆碱(50~75 mg/L)可特异性地兴奋肌梭,使大鼠比目鱼肌离体单一肌梭传入放电明显增多;氯化琥珀胆碱浓度过高(≥125mg/L)反而会抑制大鼠比目鱼肌离体单一肌梭的传入放电。     

硝苯地平对去负荷比目鱼肌肌球蛋白重链(MHC)异构体转化的影响

目的观测L型钙离子通道抑制剂硝苯地平对尾部悬吊大鼠比目鱼肌重量,以及肌球蛋白重链(MHC)表达水平的影响。方法经饮水每天给予大鼠10mg／kg体重的硝苯地平1与2周。称量比目鱼肌(SOL)与趾长伸肌(EDL)的湿重,用低温SDS-聚丙烯酰胺凝胶电泳观测MHC异构体蛋白表达,并用RT—PCR方法观测MHCmRNA的表达。结果与正常对照组相比,给予硝苯地平处理1与2周的同步对照组大鼠SOL的相对重量未见明显改变;而尾部悬吊1周与2周大鼠SOL的相对重量则分别降低了39．5％和51．7％。经硝苯地平处理的1与2周悬吊大鼠的SOL相对重量较其对照组分别降低了36．6％与52．0％,但与同步悬吊组相比,无明显差异。各组EDL相对重量均未见明显改变。正常对照组与经硝苯地平处理的对照组可检测到MHCⅠ、Ⅱa mRNA与蛋白的表达,悬吊组与经硝苯地平处理的悬吊组可检测到MHCⅠ、Ⅱa、Ⅱb与Ⅱx mRNA以及MHCⅠ与Ⅱa蛋白的表达。在对照组与悬吊组,硝苯地平对Ⅱ型MHC mRNA表达均产生抑制作用,并降低MHC Ⅱa蛋白表达。结论硝苯地平不能防止去负荷引起的SOL萎缩,但在转录水平抑制萎缩SOL的MHC异构体由慢型向快型转化。     

尾部悬吊与30月龄大鼠比目鱼肌的形态学特征比较

目的 观察尾部悬吊和30月龄大鼠比目鱼肌发生萎缩过程的异同点.方法 SD雄性大鼠42只,随机分为7组,即尾部悬吊5 d、7 d、14 d组,相应的同步对照和30月鼠龄组,在各时间点制备比目鱼肌横截面冰冻切片标本,用抗MHC Ⅱ单克隆抗体进行免疫组织化学染色,计算比目鱼肌Ⅰ、Ⅱ型肌纤维横截面积并计数各型肌纤维数目.结果 与同步对照组相比,悬吊组大鼠比目鱼肌的湿重,相对湿重,Ⅰ、Ⅱ型肌纤维横截面积,经体重归一化的肌纤维横截面积均显著降低,Ⅱ型肌纤维比例显著增加,而Ⅰ型肌纤维比例减少.与14 d对照组相比,30月龄组大鼠比目鱼肌湿重和Ⅰ、Ⅱ型肌纤维横截面积均明显增大,但其相对湿重和经体重归一化的肌纤维横截面积却显著降低,与悬吊14 d组无显著差异.30月龄组大鼠比目鱼肌中Ⅰ、Ⅱ型肌纤维比例与各对照组相比亦无显著差异.结论 30月龄大鼠比目鱼肌萎缩以首先出现相对湿重与归一化肌纤维横截面积降低为特征,且发生较慢,而尾部悬吊大鼠比目鱼肌则在较短时间内发生全面萎缩.     

Architectural alterations of rat hind-limb skeletal muscles immobilized at different lengths

Modifications in architectural profiles of the rat soleus (Sol), medial gastrocnemius (MG), and tibialis anterior (TA) muscles were studied after hind-limb immobilization with an external brace. The muscles were chronically lengthened, shortened, or maintained at approximately resting length (neutral) for 4 weeks, when muscle weight and length, and cross-sectional areas of fibers (F-XSA) and whole muscle were measured. Compared with control muscles, the Sol and MG immobilized in a lengthened position were able to maintain muscle weight better than when immobilized neutrally (approximately 85 versus 55% of control weight) due, in part, to elongation of muscle fibers of the Sol and MG (123 and 111% of control length, respectively). In addition, the F-XSAs of lengthened Sol and MG muscles were 72 and 20% greater, respectively, compared with neutrally fixed muscle fibers. Immobilization in a shortened position resulted in the most extreme muscle atrophy due to significantly shorter fibers (86% of control Sol; 74% of control MG) and reduced F-XSA (42% of control Sol; 42% of control MG). In contrast to the Sol and MG, muscle weight, fiber length, and F-XSA of the TA immobilized with the ankle in extreme plantarflexion were not significantly different from neurtrally fixed muscle. That the TA was unaffected in this position is due presumably to a difference in the anatomic attachment of the distal tendon of this muscle, compared with that of the Sol and MG. These results suggest that for muscle affected by immobilization at extreme joint angles, chronic lengthening is a potent stimulus for elongation of muscle fibers and more normally maintained F-XSA. In contrast, the removal of this stimulus leads to extreme muscle atrophy which is manifested by reductions in both muscle fiber length and F-XSA.