Thompson L V, Johnson S A, Shoeman J A
Program in Physical Therapy, University of Minnesota, Minneapolis, Minnesota 55455, USA.
J Appl Physiol (1985). 1998 Jun;84(6):1937-42. doi: 10.1152/jappl.1998.84.6.1937.
This investigation compared how hindlimb unweighting (HU) affected the contractile function of single soleus muscle fibers from 12- and 30-mo-old Fischer 344 Brown Norway F1 Hybrid rats. After 1 wk of HU, functional properties of single permeabilized fibers were studied, and, subsequently, the fiber type was established by myosin heavy chain (MHC) analysis. After HU, the relative mass of soleus declined by 12 and 19% and the relative mass of the gastrocnemius declined by 15 and 13% in 12- and 30-mo-old animals, respectively. In 12-mo-old animals, the peak active force (5.0 +/- 0.2 x10(-4) vs. 3.8 +/- 0.2 x10(-4) N) and the peak specific tension (92 +/- 4 vs. 78 +/- 3 kN/m2) were significantly reduced in the MHC type I fibers by 24 and 15%, respectively. In 30-mo-old animals, the peak active force declined by 40% (4.7 +/- 0.2 x10(-4) vs. 2.8 +/- 0. 3 x10(-4) N) and the peak specific tension declined by 30% (79 +/- 5 vs. 55 +/- 4 kN/m2). The maximal unloaded shortening velocity of the MHC type I fibers increased in 12-mo-old animals (from 1.65 +/- 0.12 to 2.59 +/- 0.26 fiber lengths/s) and in 30-mo-old animals (from 0.90 +/- 0. 09 to 1.50 +/- 0.10 fiber lengths/s) after HU. Collectively, these data suggest that the effects of HU on single soleus skeletal muscle fiber function occur in both age groups; however, the single MHC type I fibers from the older animals show greater changes than do single MHC type I fibers from younger animals.
本研究比较了后肢去负荷（HU）对12月龄和30月龄Fischer 344 Brown Norway F1杂交大鼠比目鱼肌单根肌纤维收缩功能的影响。HU处理1周后，研究了单个透化纤维的功能特性，随后通过肌球蛋白重链（MHC）分析确定纤维类型。HU处理后，12月龄和30月龄动物的比目鱼肌相对质量分别下降了12%和19%，腓肠肌相对质量分别下降了15%和13%。在12月龄动物中，MHC I型纤维的峰值主动力（5.0±0.2×10⁻⁴ vs. 3.8±0.2×10⁻⁴ N）和峰值比张力（92±4 vs. 78±3 kN/m²）分别显著降低了24%和15%。在30月龄动物中，峰值主动力下降了40%（4.7±0.2×10⁻⁴ vs. 2.8±0.3×10⁻⁴ N），峰值比张力下降了30%（79±5 vs. 55±4 kN/m²）。HU处理后，12月龄动物和30月龄动物的MHC I型纤维的最大无负荷缩短速度均增加（分别从1.65±0.12增加到2.59±0.26肌纤维长度/秒，从0.90±0.09增加到1.50±0.10肌纤维长度/秒）。总体而言，这些数据表明，HU对单个比目鱼肌骨骼肌纤维功能的影响在两个年龄组中均会出现；然而，老年动物的单个MHC I型纤维比年轻动物的单个MHC I型纤维变化更大。
