钙调神经磷酸酶在耐力运动大鼠骨骼肌纤维类型和大小转变中的作用

The Role of Calcineurin in the Changes in Skeletal Muscle Fiber Type and Size of Rats Induced by Endurance Exercise

目的:探讨钙调神经磷酸酶(CaN)在耐力运动时骨骼肌纤维类型和大小转变中的作用。方法:雄性SD大鼠(150~200g)随机分成对照组和运动组。运动组大鼠进行6周无坡度跑台训练(20m/min^28m/min),并在第3周末进一步随机分成2组:运动+环孢素组,皮下注射环孢素(CSA,15mg/kg体重/day)3周;单纯运动组,注射等量生理盐水。各组大鼠第6周末取比目鱼肌和趾长伸肌,分别用SDS-PAGE电泳法和肌纤维ATP酶染色法测定肌球蛋白重链(MHC)组成比例和肌纤维横断面积,同时用比色法测CaN活性,并用Westernblotting法测CaN和活化T细胞核因子2(NFAT2)蛋白含量。结果:单纯运动组大鼠比目鱼肌MHCⅠ比例(93.4±6.0%)显著高于对照组(82.7±6.6%),而运动+环孢素组大鼠MHCⅠ比例(79.3±8.4%)无增加,但其Ⅰ型肌纤维横断面积显著小于对照组和单纯运动组(P<0.05)。单纯运动组大鼠趾长伸肌胞浆CaN活性及胞核NFAT2蛋白含量显著高于对照组(P<0.05),但纤维比例无显著改变(P>0.05);运动+环孢素组大鼠趾长伸肌肌原纤维蛋白浓度显著高于单纯运动组(P<0.05),且该组各型肌纤维横断面积均显著小于对照组和单纯运动组(P<0.05)。结论:CaN参与了耐力运动骨骼肌纤维类型和大小的调控,且具有肌肉特异性。

Objective To explore the role of calcineurin （CAN） in the changes of skeletal muscle fiber type and size induced by endurance training. Methods Male SD rats （150-200g） were randomized into control group and exercise group. Rats in exercise group performed endurance training on a motor-driven rodent treadmill （0 incline） 1 hour per day at the speed of 28m/min, for 6 weeks. At the end of the 3rd week, half of the rats in exercise group were injected with cyclosporine （CSA, 15rag per kg. BW per day） hypodermically for 3 weeks （exercise plus CSA group）, the remains were injected with saline at the same time （pure exercise group）. After 6 weeks of experiment, soleus muscle （SOL） and extensor digitorum longus muscle （EDL） were harvested. The proportion of myosin heavy chain （MHC） isoforms and cross sectional area of fibers by electrophoretic approach and ATPase staining, CaN activity by colorimetry, CaN and nuclear factor of activated T cells （NFAT2） protein content by Western blotting were performed. Results Myosin heavy chain （MHC） I ratio of SOL in pure exercise group（93.4 ± 6.0% ）was significantly higher than that in control group（82.7±6.6 % ）and exercise plus CSA group（79.3±8.4% ）respectively, cross sectional area of fiber in exercise plus CSA group was smaller than that in control group and pure exercise group（P〈0.05）. As compared with control group, cytoplasmic CaN activity and nuclear protein content of NFAT2 in EDL increased significantly in exercise group （P%0.05） without changing in fiber type composition （P〉0.05）. Myofibril protein content of EDL was significantly higher in exercise plus CSA group than that in pure exercise group （P〈0.05）, and cross-section area of all types of fibers in EDL was significantly lower in exercise plus CSA group than in control group and pure exercise group （P〈0. 05）. Conclusions CaN involved in regulation of skeletal muscle fiber type and size as a muscle-specific factor during the endurance training.