Schuenke Mark D, Reed David W, Kraemer William J, Staron Robert S, Volek Jeff S, Hymer Wesley C, Gordon Scott, Perry Koziris L
Department of Anatomy, College of Osteopathic Medicine, University of New England, 431 Stella Maris, Biddeford, NE 04005, USA.
Eur J Appl Physiol. 2009 Aug;106(6):885-92. doi: 10.1007/s00421-009-1091-9. Epub 2009 May 31.
The purpose of the present study was to determine the effects of 14 days of microgravity on specific rat fast-twitch muscles, and to compare these data with previous data from rat fast-twitch muscles exposed to microgravity for 10 days (Kraemer et al. 2000). Hindlimb muscles containing predominately fast fibers [extensor digitorum longus (EDL), superficial "white" (GSW) and deep "red" (GDR) gastrocnemius] and the diaphragm (DIA) were removed from flight and ground-based control animals and analyzed for: muscle mass, fiber type distribution, cross-sectional area, and myosin heavy chain (MHC) isoform content. Gravitational unloading for 14 days caused significant decreases in muscle mass (8-9%) and cross-sectional area of almost all fiber types (10-35%) from both EDL and gastrocnemius muscles. However, microgravity had little effect on fiber type composition in these muscles with significant changes occurring only in the EDL type IID fiber population (9.5% decrease). Similarly, relative MHC isoform content was only slightly altered by exposure to microgravity (increased content of MHCIIa in flight EDL). No changes in area, fiber type percentages, or MHC isoform content were detected in the DIA following the 14-day spaceflight. Similar to data gathered following a 10-day spaceflight (Kraemer et al. 2000), the 14-day flight did not appear to cause significant slow-to-fast (I --> IIA) or fast-to-faster (IIA --> IID --> IIB) transformations in hindlimb muscles containing predominantly fast-twitch fibers. However, the longer period of gravitational unloading did result in additional loss in muscle fiber cross-sectional area with involvement of more major fiber types.
本研究的目的是确定14天微重力对大鼠特定快肌的影响，并将这些数据与之前大鼠快肌在微重力环境下暴露10天的数据（Kraemer等人，2000年）进行比较。从飞行和地面对照动物身上取出主要含有快肌纤维的后肢肌肉[趾长伸肌（EDL）、浅层“白色”（GSW）和深层“红色”（GDR）腓肠肌]以及膈肌（DIA），并对其进行以下分析：肌肉质量、纤维类型分布、横截面积和肌球蛋白重链（MHC）亚型含量。14天的重力卸载导致EDL和腓肠肌的肌肉质量显著下降（8 - 9%），几乎所有纤维类型的横截面积都显著减小（10 - 35%）。然而，微重力对这些肌肉的纤维类型组成影响很小，仅EDL的IID型纤维群体发生了显著变化（减少9.5%）。同样，暴露于微重力环境下，相对MHC亚型含量仅略有改变（飞行组EDL中MHCIIa含量增加）。14天太空飞行后，未检测到膈肌在面积、纤维类型百分比或MHC亚型含量方面有变化。与10天太空飞行后收集的数据（Kraemer等人，2000年）相似，14天的飞行似乎并未导致主要含有快肌纤维的后肢肌肉发生显著的慢到快（I型→IIA型）或快到更快（IIA型→IID型→IIB型）转变。然而，更长时间的重力卸载确实导致肌肉纤维横截面积进一步减小，且涉及更多主要纤维类型。
