Thompson L V, Shoeman J A
Program in Physical Therapy, University of Minnesota, Minneapolis 55455, USA.
J Appl Physiol (1985). 1998 Jan;84(1):229-35. doi: 10.1152/jappl.1998.84.1.229.
This investigation determined how muscle atrophy produced by hindlimb unweighting (HU) alters the contractile function of single muscle fibers from older animals (30 mo). After 1 wk of HU, small bundles of fibers were isolated from the soleus muscles and the deep region of the lateral head of the gastrocnemius muscles. Single glycerinated fibers were suspended between a motor lever and force transducer, functional properties were studied, and the myosin heavy chain (MHC) composition was determined electrophoretically. After HU, the diameter of type I MHC fibers of the soleus declined (88 +/- 2 vs. 80 +/- 4 microns) and reductions were observed in peak active force (47 +/- 3 vs. 28 +/- 3 mg) and peak specific tension (Po; 80 +/- 5 vs. 56 +/- 5 kN/m2). The maximal unloaded shortening velocity increased. The type I MHC fibers from the gastrocnemius showed reductions in diameter (14%), peak active force (41%), and Po (24%), whereas the type IIa MHC fibers showed reductions in peak active force and Po. Thus 1 wk of inactivity has a significant effect on the force-generating capacity of single skeletal muscle fibers from older animals in a fiber type-specific manner (type I MHC > type IIa MHC > type I-IIa MHC). The decline in the functional properties of single skeletal muscle fibers in the older animals appears to be more pronounced than what has been reported in younger animal populations.
本研究确定了后肢去负荷（HU）导致的肌肉萎缩如何改变老年动物（30月龄）单根肌纤维的收缩功能。HU处理1周后，从比目鱼肌和腓肠肌外侧头深部分离出小束纤维。将单根甘油化纤维悬于运动杠杆和力传感器之间，研究其功能特性，并通过电泳测定肌球蛋白重链（MHC）组成。HU处理后，比目鱼肌I型MHC纤维的直径减小（88±2微米对80±4微米），峰值主动力（47±3毫克对28±3毫克）和峰值比张力（Po；80±5千牛/平方米对56±5千牛/平方米）降低。最大无负荷缩短速度增加。腓肠肌的I型MHC纤维直径减小（14%），峰值主动力（41%）和Po（24%）降低，而IIa型MHC纤维的峰值主动力和Po降低。因此，1周的不活动对老年动物单根骨骼肌纤维的力产生能力有显著影响，且具有纤维类型特异性（I型MHC>IIa型MHC>I-IIa型MHC）。老年动物单根骨骼肌纤维功能特性的下降似乎比年轻动物群体中报道的更为明显。
