Changes in the contractile function of gastrocnemius myosin after aerobic exercise
- VernacularTitle:腓肠肌肌球蛋白收缩功能在有氧训练后的变化
- Author:
Wenjun REN
- Publication Type:Journal Article
- From:
Chinese Journal of Tissue Engineering Research
2007;11(10):1996-2000
- CountryChina
- Language:Chinese
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Abstract:
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.
