Gregory Chris M, Vandenborne Krista, Castro Michael J, Dudley G Alton
Dept. of Physical Therapy, Texas Woman's University, 1130 J. Freeman Blvd., Houston, TX 77030-2897, USA.
Can J Appl Physiol. 2003 Jun;28(3):491-500. doi: 10.1139/h03-036.
Results of studies of rodent skeletal muscle plasticity are often extrapolated to humans. However, responses to "disuse" may be species specific, in part because of different inherent properties of anatomically similar muscles. Thus, this study quantified human and rat m. vastus lateralis (VL) fiber adaptations to 11 weeks of spinal cord injury (SCI). The m. VL was taken from 8 young (54 d) male Charles River rats after T-9 laminectomy (n = 4) or sham surgery (n = 4). In addition, the m. VL was biopsied in 7 able-bodied and in 7 SCI humans (31.3 +/- 4.7 years, mean +/- SE). Samples were sectioned and fibers were analyzed for type (I, IIa, IIb/x), cross-sectional area (CSA), succinate dehydrogenase (SDH), alpha-glycerol-phosphate dehydrogenase (GPDH), and actomyosin adenosine triphosphatase (qATPase) activities. Rat fibers had 1.5- to 2-fold greater SDH and GPDH activities while their fibers were 60% the size of those in humans. The most striking differences, however, were the absence of slow fibers in the rat and its four-fold greater proportion of IIb/x fibers (80% vs. 16% of the CSA) compared to humans. SCI decreased SDH activity more in rats whereas atrophy and IIa to IIb/x fiber shift occurred to a greater extent in humans. It is suggested that the rat is a reasonable model for studying the predominant response to SCI, atrophy. However, its high proportion of IIb/x fibers limits evaluation of the mechanical consequences of shifting to "faster" contractile machinery after SCI.
对啮齿动物骨骼肌可塑性的研究结果常常被外推到人类身上。然而，对“废用”的反应可能具有物种特异性，部分原因是解剖结构相似的肌肉具有不同的固有特性。因此，本研究量化了人类和大鼠股外侧肌（VL）在脊髓损伤（SCI）11周后的纤维适应性变化。从8只年轻（54日龄）雄性查尔斯河大鼠身上获取股外侧肌，其中4只接受T-9椎板切除术，另4只接受假手术。此外，对7名健康人和7名脊髓损伤患者（年龄31.3±4.7岁，均值±标准误）的股外侧肌进行活检。将样本切片，分析纤维的类型（I型、IIa型、IIb/x型）、横截面积（CSA）、琥珀酸脱氢酶（SDH）、α-甘油磷酸脱氢酶（GPDH）以及肌动球蛋白腺苷三磷酸酶（qATPase）活性。大鼠纤维的SDH和GPDH活性比人类高1.5至2倍，但其纤维大小仅为人类纤维的60%。然而，最显著的差异在于大鼠缺乏慢肌纤维，且与人类相比，其IIb/x纤维的比例大四倍（占CSA的80% vs. 16%）。脊髓损伤后，大鼠的SDH活性下降更为明显，而人类则出现了更严重的萎缩以及IIa型纤维向IIb/x型纤维的转变。研究表明，大鼠是研究脊髓损伤主要反应——萎缩的合理模型。然而，其高比例的IIb/x纤维限制了对脊髓损伤后转向“更快”收缩机制所产生机械后果的评估。
