下坡运动对大鼠骨骼肌肌浆网功能的影响

目的：观测研究下坡(离心)运动对大鼠骨骼肌肌浆网Ca2+-ATP酶活性,Ca2+摄取与释放在量与时程上的影响。此外,测定离子载体的刺激作用,即测定在含与不含(Ca2+离子载体)A23187时Ca2+-ATP酶活性的比值,用以评定囊泡的完整性。方法：成年雄性SD大鼠随机分为对照与离心运动组, 离心运动的大鼠分别于运动后即刻, 4, 24, 48, 72 和144h后取样 (n=7). 离心运动方式采用90min持续跑台下坡运动(-16°;15m/min)。取大鼠红股肌制备组织匀浆, 测定肌浆网Ca2+-ATP酶活性,Ca2+摄取与释放。结果：与对照组19.25±1.38 nmol ·min-1·(mg protein)-1]相比, 肌浆网Ca2+摄取分别于运动后即刻和4h下降了29% and 36% (P<0.05), 24h依然降低(P<0.05). 肌浆网Ca2+释放与对照组31.06±2.36 nmol·min-1·(mg protein)-1] 相比,也分别于运动后即刻和4h下降了37% and 39% (P<0.05), 24h持续降低(P<0.05). 用含离子载体测定的肌浆网Ca2+-ATP酶活性运动后4h降低了31%(P<0.05), 并于运动后24h仍然降低 (P<0.05)。运动后, 含与不含A23187时测定的Ca2+-ATP酶活性的比值未见显著性改变, 表明该运动没有明显改变肌浆网膜的完整性。结论：一次性低强度，长时间下坡运动导致肌浆网功能长时间降低, 运动后恢复期两天尚未完全恢复, 亦可构成离心运动诱导的骨骼肌某些功能降低的基础。提示这些变化可能产生于离心收缩时肌节长度不匀一性所造成的张力应激。

Effect of downhill exercise on sarcoplasmic reticulum function in rat skeletal muscle

Objective: To investigate the effect of downhill (eccentric) exercise (ECE) on sarcoplasmic reticulum (SR) Ca2+-ATPase activity, Ca2+ uptake and release in rat skeletal muscle, in terms of both magnitude and time course. In addition, ionophore stimulation was determined to assess vesicle integrity by measuring the ratio of calcium-dependent ATPase activities in the presence and absence of A23187. Method: Adult male SD rats were randomly assigned to control and ECE groups. The ECE rats were sacrificed at the 0th, 4th, 24th, 48th, 72nd and 144th h following ECE (n=7). The ECE protocol consisted of 90min continuous downhill exercise (-16 deg; 15m·min-1). Red vastus muscles were sampled separately for each group and muscle homogenates were prepared. The rates of SR Ca2+-ATPase activity, Ca2+ uptake and release were measured in vitro. Result: SR Ca2+ uptake was significantly lower (P<0.05) compared with control values 19.25±1.38 nmol·min-1·(mg protein)-1], by 29% and 36% immediately and 4h after ECE, respectively, and remained depressed (P<0.05) 24h following ECE. SR Ca2+ release was also significantly lower(P<0.05) compared with control values 31.06±2.36nmol·min-1·(mg protein)-1], by 37% and 39% immediately and 4h after ECE, respectively, and remained depressed(P<0.05) 24h following ECE. SR Ca2+-ATPase activity measured with ionophore was 31% lower (P<0.05) 4h after ECE, and remained lower (P<0.05) 24h following ECE. The ratio of Ca2+-ATPase activities in the presence and absence of A23187 was not significantly changed following ECE, indicating that membrane integrity was not altered by the exercise. Conclusion: The present results suggest that a bout of low-intensity, prolonged downhill exercise results in a long-lasting depression of SR function that is not fully restored after two days of recovery, which may underlie some muscle functional impairments induced by ECE. These changes could be the results of stress from sarcomere length inhomogeneities during eccentric contractions.