Graduate School of Medicine, Osaka University, Toyonaka City, Osaka 560-0043, Japan.
J Appl Physiol (1985). 2010 Mar;108(3):676-85. doi: 10.1152/japplphysiol.00478.2009. Epub 2010 Jan 7.
Effects of gravitational loading or unloading on the gain of the characteristics in soleus muscle fibers were studied in rats. The tail suspension was performed in newborn rats from postnatal day 4 to month 3, and the reloading was allowed for 3 mo in some rats. Single expression of type I myosin heavy chain (MHC) was observed in approximately 82% of fibers in 3-mo-old controls, but the fibers expressing multiple MHC isoforms were noted in the unloaded rats. Although 97% of fibers in 3-mo-old controls had a single neuromuscular junction at the central region of fiber, fibers with multiple nerve endplates were seen in the unloaded group. Faster contraction speed and lower maximal tension development, even after normalization with fiber size, were observed in the unloaded pure type I MHC fibers. These parameters generally returned to the age-matched control levels after reloading. It was suggested that antigravity-related tonic activity plays an important role in the gain of single neural innervation and of slow contractile properties and phenotype in soleus muscle fibers.
本研究旨在探讨重力加载或卸载对大鼠比目鱼肌纤维特性增益的影响。从出生后第 4 天到第 3 个月，对新生大鼠进行尾部悬吊，部分大鼠允许重新加载 3 个月。3 个月大的对照组中约有 82%的纤维单表达 I 型肌球蛋白重链（MHC），但在未加载的大鼠中观察到表达多种 MHC 同工型的纤维。尽管 3 个月大的对照组中 97%的纤维在纤维的中央区域具有单个运动终板，但在未加载的组中观察到具有多个神经终板的纤维。在未加载的纯 I 型 MHC 纤维中，观察到更快的收缩速度和更低的最大张力发展，即使在与纤维大小归一化后也是如此。这些参数在重新加载后通常恢复到与年龄匹配的对照组水平。研究结果表明，与抗重力相关的紧张活动在比目鱼肌纤维中单根神经支配和慢收缩特性及表型的获得中发挥重要作用。
