Maréchal G, Coulton G R, Beckers-Bleukx G
Département de Physiologie, Faculté de médecine, Université Catholique de Louvain, Brussels, Belgium.
Am J Physiol. 1995 Feb;268(2 Pt 1):C513-9. doi: 10.1152/ajpcell.1995.268.2.C513.
Muscles of ky/ky homozygote mice exhibit neonatal muscle fiber necrosis and regeneration with subsequent motor nerve sprouting and development of a prominent kyphoscoliosis from approximately 100 days onward. Soleus and extensor digitorum longus (EDL) muscles from ky mice weighted < 50% of control muscles from age-matched NMRI mice. Maximal tetanic force was more reduced in soleus than in EDL. In EDL, the velocity constant of the force-velocity relation, maximal velocity, twitch time-to-peak, and isomyosin content were normal at all ages. The early mechanical changes seen in ky soleus muscles (47 day) were not accompanied by significant alterations in isomyosin or myosin heavy- and light-chain composition, since ky and NMRI expressed slow-twitch native myosin 2 (SM2, type I fibers) and intermediate-twitch native myosin (IM, type IIa fibers). Adult ky soleus (172 day) showed wholesale loss of IM and sole expression of SM2. This is sufficient to account for the markedly slowing of the force-velocity relation and the twitches observed in adult ky soleus. We propose that since shifts in muscle type only occurred in soleus, this reflects the persistent requirement to withstand the force of gravity.
ky/ky纯合子小鼠的肌肉在新生儿期表现出肌纤维坏死和再生，随后运动神经发芽，并从大约100天起出现明显的脊柱侧凸。ky小鼠的比目鱼肌和趾长伸肌（EDL）的重量不到年龄匹配的NMRI小鼠对照肌肉的50%。比目鱼肌的最大强直力比EDL下降得更多。在EDL中，力-速度关系的速度常数、最大速度、单收缩峰值时间和同工肌球蛋白含量在所有年龄段均正常。在ky比目鱼肌（47天）中观察到的早期力学变化并未伴随着同工肌球蛋白或肌球蛋白重链和轻链组成的显著改变，因为ky和NMRI均表达慢收缩天然肌球蛋白2（SM2，I型纤维）和中间收缩天然肌球蛋白（IM，IIa型纤维）。成年ky比目鱼肌（172天）显示IM完全缺失，仅表达SM2。这足以解释成年ky比目鱼肌中力-速度关系和单收缩明显减慢的现象。我们认为，由于肌肉类型的转变仅发生在比目鱼肌中，这反映了持续承受重力的需求。
