腓肠肌肌球蛋白收缩功能在有氧训练后的变化(英文)

Changes in the contractile function of gastrocnemius myosin after aerobic exercise

背景:已有实验证实长期耐力训练能导致肌纤维及其肌球蛋白重链异形体由快型向慢型转变,但对于运动训练中肌球蛋白重链异形体mRNA的变化仍有待进一步的实验观察与验证。目的:观察跑台训练对雄性SD大鼠腓肠肌肌球蛋白收缩功能的影响。设计:随机对照动物实验。单位:西安交通大学医学实验中心。材料:选用40只生后7周雄性SD大鼠,体质量(230±16)g,所有动物实验前均未进行过跑台运动。试剂:一抗为鼠源性抗骨骼肌肌动蛋白及快缩型肌球蛋白重链(MHCⅡ)单克隆抗体,ABCam产品。二抗为偶合碱性磷酸酶的抗鼠IgG,SIGMA产品。方法:实验于2005-03/10在西安交通大学医学实验中心完成。随机摸球法将大鼠分为对照组(n=10)和训练组(n=30)。训练组大鼠进行连续4～6周强度约为75%VO2max(18.5～24m/min,坡度为0°)的跑台训练,50min/次,2次/d。对照组自由活动,不给予任何干预措施。训练至4,5,6周,分别取10只大鼠,采用反转录聚合酶链式反应腓肠肌肌球蛋白重链mRNA含量,以免疫组化方法检测肌球蛋白肌纤维的改变情况及横截面积的大小,大鼠麻醉后游离腓肠肌,采用张力传感器及电刺激器给予方波脉冲刺激,逐步拉伸腓肠肌至等长收缩张力为最大时的肌肉初长Lmax位置,平衡10min,记录肌肉长度与张力。取右侧腓肠肌称量湿质量,计算其与体质量之比。肌肉质量与体质量之比按下式计算:肌肉质量(mg)/体质量(g)×100%。主要观察指标:①腓肠肌肌球蛋白重链mRNA含量。②肌球蛋白肌纤维的改变情况及横截面积的大小。③大鼠体质量与腓肠肌质量的变化。④腓肠肌等长收缩最大张力。结果:纳入大鼠40只全部进入结果分析。①腓肠肌肌球蛋白重链mRNA含量:经过4周耐力训练,训练组肌球蛋白总肌球蛋白重链表达是对照组的105%(P<0.01),肌球蛋白重链Ⅱa表达量高于对照组(1.27±0.08,1.17±0.06,P<0.05),肌球蛋白重链ⅡxmRNA表达量高于对照组(1.29±0.04,1.19±0.05,P<0.01)。②肌球蛋白肌纤维的改变情况及横截面积的大小:经过4～6周的有氧训练后,大鼠肌球蛋白重链主要以Ⅱ型慢缩型肌纤维表达为主,而Ⅰ型快缩型肌纤维表达较少。对照组大鼠腓肠肌Ⅰ、Ⅱ型肌纤维横截面积分别为(1958.0±30.5),(1656.1±35.3)mm2。而训练组4周后Ⅰ、Ⅱ型肌纤维横截面积较对照组分别增加24.5%与22.1%(P<0.01);训练组5周后分别增加26.4%与51.5%(P<0.01),训练组训练6周后分别增加33.2%与48.9%(P<0.01)。③大鼠体质量与腓肠肌质量的变化:训练组大鼠训练4,5,6周腓肠肌湿质量分别为(135.6±3.1),(139.2±5.1),(148.4±6.2)mg,高于对照组[(103.2±3.4),(87.5±2.9),(68.3±3.3)mg,P<0.01]。训练组大鼠训练4,5,6周腓肠肌相对湿质量分别为(0.55±0.01),(0.56±0.02),(0.59±0.03),高于对照组[(0.43±0.02),(0.37±0.04),(0.29±0.05),P<0.05～0.01]。④腓肠肌等长收缩最大张力:方波脉冲刺激后6周训练组等长收缩最大张力较对照组显著增加(P<0.01)。结论:短期耐力训练后,肌球蛋白重链中的两种慢型肌球蛋白重链异形体-肌球蛋白重链Ⅱx、肌球蛋白重链Ⅱb基因表达增加,肌纤维横截面积增加,等长收缩最大张力增加,表明有氧训练对提高肌球蛋白收缩功能有促进作用。

BACKGROUND：It is reported that long-term endurance training can induce the transformation of muscle fibers and the myosin heavy chain （MHC） isoforms from the fast type into the slow type. But the change of MHC isoforms mRNAs in the movement training needs further study.OBJECTIVE： To observe the effect of the treadmill training on the contractile function of gastrocnemius MHC in male SD rats.DESIGN： A randomized controlled animal experiment.SETTING： Medical Experimental Center of Xi＇an Jiaotong University.MATERIALS： Totally 40 male SD rats aged 7 weeks with the body mass of （230±16） g were selected. All the animals had not experienced the treadmill exercise before the experiment. Reagents： The primary antibodies were the murine anti-actin and anti-MHC Ⅱ of fast contractile type of skeletal muscle monoclonal antibodies, ABCam products. The secondary antibody was the alkaline phosphatase-conjugated anti-murine IgG, SIGMA product.METHODS： The experiment was conducted at the Medical Experimental Center of Xi＇an Jiaotong University from March to October 2005. All the rats were randomly assigned into control group （n =10） and training group （n =30）. The rats in the training group took movement training for 4-6 weeks with the exercise intensity of 75%VO2max （18.5-24 m/min,gradient of 0°）, once 50 minutes and twice a day. The rats in the control group did free exercise, and did not receive any intervention. At weeks 4, 5 and 6, MHC mRNA content was measured by reverse transcription-polymerase chain reaction （RT-PCR） and change of myosin muscle fibers and size of cross section area （CSA） were determined by immunohistochemical method in 10 rats. The rats were anesthetized before the gastrocnemius liberated gently. Tension transducer and electrical stimulator were applied to give square wave pulse stimulation. The gastrocnemius was extended gradually till the Lmax position of initial length of muscle, at which the isometric contraction tension reached the maximal value for 10 minutes. The muscle length and tension were recorded. The right-side gastrocnemius was obtained to measure the wet weight, and the ratio with the body mass was calculated. The ratio of muscle mass to body mass was determined by the following formula： muscle mass （mg）/body mass （g） ×100%.MAIN OUTCOME MEASURES： ①MHC mRNA content of gastrocnemius, ②change of myosin muscle fibers and size of CSA, ③body mass of rats and gastrocnemius mass, and ④maximal tension of isometric contraction of gastrocnemius.RESULTS： A total of 40 included rats were involved in the result analysis. ①MHC mRNA content of gastrocnemius： The expression of total MHC mRNA of the training group was 105% of that of the control group after the endurance training for 4 weeks （P 〈 0.01）. The expression of MHC Ⅱ a was higher than that in the control group （1.27±0.08,1.17±0.06, P 〈 0.05）. The expression of MHC Ⅱ x mRNA was higher than that in the control group （1.29±0.04,1.19±0.05, P 〈 0.01 ）.②change of myosin muscle fibers and size of CSA： the MHC of rats had the main expression of the Ⅱ slow contractile type of muscle fibers, but less expression of Ⅰ fast contractile type of muscle fibers ratio after 4-6 weeks aerobic exercise. The CSA of type Ⅰ and type Ⅱ muscle fibers of the rats in the control group were （1 958.0±30.5）, （1 656.1± 35.3） μm2, respectively. However, as compared with the control group, the CSA of type I and type Ⅱ muscle fibers of the rats in the four-week-training group increased by 24.5 % and 22.1% （P 〈 0.01） respectively. In the five-week-training group, the related value increased by 26.4 % and 51.5 % （P 〈 0.01）, respectively. In the six-week-training group, the related value increased by 33.2% and 48.9% （P 〈 0.01）, respectively. ③body mass of rats and gastrocnemius mass：The wet weight of gastrocnemius [（135.6±3.1 ）, （139.2±5.1）, （148.4±6.2） mg] was higher in the training group than the control group [（103.2±3.4）, （87.5±2.9）, （68.3±3.3） mg,P 〈 0.01] at weeks 4, 5 and 6. Relative weight of gastrocnemius [（0.55±0.01）, （0.56±0.02）, （0.59±0.03）] was higher in the training group than the control group [（0.43±0.02）, （0.37± 0.04）, （0.29±0.05）,P 〈 0.05-0.01] at weeks 4, 5 and 6. ④maximal tension of isometric contraction of gastrocnemius：The maximal tension of isometric contraction increased significantly in the training group as compared with the control group after square wave pulse stimulation at week 6 （P 〈 0.01）.CONCLUSION： Expression of MHC Ⅱ x and MHC Ⅱ b, the CSA of muscle fibers and the maximal tension of isometric contraction are all increased after the short-term endurance training. It indicates that the aerobic exercise may promote the contractile function of MHC.