Castro M J, Apple D F, Staron R S, Campos G E, Dudley G A
Department of Exercise Science, The University of Georgia, Athens 30602, USA.
J Appl Physiol (1985). 1999 Jan;86(1):350-8. doi: 10.1152/jappl.1999.86.1.350.
This study examined the influence of spinal cord injury (SCI) on affected skeletal muscle. The right vastus lateralis muscle was biopsied in 12 patients as soon as they were clinically stable (average 6 wk after SCI), and 11 and 24 wk after injury. Samples were also taken from nine able-bodied controls at two time points 18 wk apart. Surface electrical stimulation (ES) was applied to the left quadriceps femoris muscle to assess fatigue at these same time intervals. Biopsies were analyzed for fiber type percent and cross-sectional area (CSA), fiber type-specific succinic dehydrogenase (SDH) and alpha-glycerophosphate dehydrogenase (GPDH) activities, and myosin heavy chain percent. Controls showed no change in any variable over time. Patients showed 27-56% atrophy (P = 0.000) of type I, IIa, and IIax+IIx fibers from 6 to 24 wk after injury, resulting in fiber CSA approximately one-third that of controls. Their fiber type specific SDH and GPDH activities increased (P </= 0.001) from 32 to 90% over the 18 wk, thereby approaching or surpassing control values. The relative CSA of type I fibers and percentage of myosin heavy chain type I did not change. There was apparent conversion among type II fiber subtypes; type IIa decreased and type IIax+IIx increased (P </= 0.012). Force loss during ES did not change over time for either group but was greater (P = 0.000) for SCI patients than for controls overall (27 vs. 9%). The results indicate that vastus lateralis muscle shows marked fiber atrophy, no change in the proportion of type I fibers, and a relative independence of metabolic enzyme levels from activation during the first 24 wk after clinically complete SCI. Over this time, quadriceps femoris muscle showed moderately greater force loss during ES in patients than in controls. It is suggested that the predominant response of mixed human skeletal muscle within 6 mo of SCI is loss of contractile protein. Therapeutic interventions could take advantage of this to increase muscle mass.
本研究考察了脊髓损伤（SCI）对受影响骨骼肌的影响。12例患者临床病情稳定后（脊髓损伤后平均6周）、损伤后11周和24周时，对其右侧股外侧肌进行活检。还在9名健康对照者相隔18周的两个时间点采集样本。在相同时间间隔，对左侧股四头肌施加表面电刺激（ES）以评估疲劳情况。对活检样本分析纤维类型百分比和横截面积（CSA）、纤维类型特异性琥珀酸脱氢酶（SDH）和α-甘油磷酸脱氢酶（GPDH）活性以及肌球蛋白重链百分比。对照者各变量随时间无变化。患者在损伤后6至24周，I型、IIa型和IIax + IIx型纤维出现27% - 56%的萎缩（P = 0.000），导致纤维CSA约为对照者的三分之一。其纤维类型特异性SDH和GPDH活性在18周内增加了32%至90%（P≤0.001），从而接近或超过对照值。I型纤维的相对CSA和I型肌球蛋白重链百分比未改变。II型纤维亚型之间存在明显转变；IIa型减少，IIax + IIx型增加（P≤0.012）。两组在ES期间的力量损失随时间均无变化，但总体上脊髓损伤患者的力量损失大于对照者（P = 0.000）（27%对9%）。结果表明，股外侧肌在临床完全性脊髓损伤后的前24周内出现明显的纤维萎缩，I型纤维比例无变化，代谢酶水平与激活相对独立。在此期间，股四头肌在电刺激时患者的力量损失比对照者略大。提示脊髓损伤6个月内混合性人体骨骼肌的主要反应是收缩蛋白的丧失。治疗干预可利用这一点来增加肌肉质量。
