Malformed mdx myofibers have normal cytoskeletal architecture yet altered EC coupling and stress-induced Ca2+ signaling
Malformed mdx myofibers have normal cytoskeletal architecture yet altered EC coupling and stress-induced Ca2+ signaling
复制标题
DOI：
10.1152/ajpcell.00087.2009
复制
发表时间：
2009-09-01
影响因子：
5.5
通讯作者：
Ward, Christopher W.
中科院分区：
文献类型：
--
作者：
Lovering, Richard M.;Michaelson, Luke;Ward, Christopher W.
洛夫林·RM、迈克尔森·L、沃德·CW。畸形的 mdx 肌纤维具有正常的细胞骨架结构，但 EC 耦合和应激诱导的 Ca2+ 信号传导发生了改变。 Am J Physiol Cell Physiol 297：C571-C580，2009。首次发表于 2009 年 7 月 15 日； doi:10.1152/ajpcell.00087.2009.-骨骼肌功能取决于其高度规则的结构。在对营养不良（dy/dy）小鼠的研究中，长时间的整块肌肉刺激后，畸形肌纤维的比例下降，这表明畸形肌纤维更容易受伤。本研究的目的是评估年轻（2-3 个月）和老年（8-9 个月）mdx 和年龄匹配对照小鼠 (C57BL10) 的指长伸肌 (EDL) 和指短屈肌 (FDB) 肌肉纤维的形态并测量兴奋-收缩 (EC) 耦合（Ca2+ 瞬态）和对渗透压（Ca2+ 火花）的敏感性。在年轻的 mdx EDL 中，6% 的肌纤维有明显的畸形（即纤维间分裂、末端分支、中纤维附属物）。相比之下，旧 mdx EDL 中 65% 的肌纤维含有可见的畸形。在 mdx FDB 中，仅 5% 的年轻肌纤维和 11% 的老年肌纤维发生畸形。年龄匹配的对照小鼠没有表现出 mdx 肌肉形态的改变。在畸形的 mdx 肌纤维中，膜相关和细胞质的细胞骨架结构显得正常。在具有显着分支末端的 mdx FDB 中，对全局电诱发 Ca2+ 信号 (indo-1PE-AM) 的评估揭示了具有显着分支的肌纤维中的 EC 耦合缺陷。有趣的是，与同一肌纤维的主干相比，分叉的 mdx 肌纤维分支中电诱发 Ca2+ 释放的峰值幅度显着降低。与正常 mdx 肌纤维相比，畸形 mdx 肌纤维的基础肌浆 Ca2+ 浓度（即吲哚比率）没有变化。最后，渗透压在肌纤维畸形部分更大程度地诱导Ca2+火花的发生，这与EC耦合控制的缺陷是一致的。总之，我们的数据表明，老化的 mdx 肌纤维会出现形态畸形。这些畸形与细胞骨架或 T 管结构的严重破坏无关；然而，肌纤维 Ca2+ 信号传导的改变是明显的。
Lovering RM, Michaelson L, Ward CW. Malformed mdx myofibers have normal cytoskeletal architecture yet altered EC coupling and stressinduced Ca2+ signaling. Am J Physiol Cell Physiol 297: C571-C580, 2009. First published July 15, 2009; doi:10.1152/ajpcell.00087.2009.-Skeletal muscle function is dependent on its highly regular structure. In studies of dystrophic (dy/dy) mice, the proportion of malformed myofibers decreases after prolonged whole muscle stimulation, suggesting that the malformed myofibers are more prone to injury. The aim of this study was to assess morphology and to measure excitation-contraction (EC) coupling (Ca2+ transients) and susceptibility to osmotic stress (Ca2+ sparks) of enzymatically isolated muscle fibers of the extensor digitorum longus (EDL) and flexor digitorum brevis (FDB) muscles from young (2-3 mo) and old (8-9 mo) mdx and age-matched control mice (C57BL10). In young mdx EDL, 6% of the myofibers had visible malformations (i.e., interfiber splitting, branched ends, midfiber appendages). In contrast, 65% of myofibers in old mdx EDL contained visible malformations. In the mdx FDB, malformation occurred in only 5% of young myofibers and 11% of old myofibers. Age-matched control mice did not display the altered morphology of mdx muscles. The membrane-associated and cytoplasmic cytoskeletal structures appeared normal in the malformed mdx myofibers. In mdx FDBs with significantly branched ends, an assessment of global, electrically evoked Ca2+ signals (indo-1PE-AM) revealed an EC coupling deficit in myofibers with significant branching. Interestingly, peak amplitude of electrically evoked Ca2+ release in the branch of the bifurcated mdx myofiber was significantly decreased compared with the trunk of the same myofiber. No alteration in the basal myoplasmic Ca2+ concentration (i.e., indo ratio) was seen in malformed vs. normal mdx myofibers. Finally, osmotic stress induced the occurrence of Ca2+ sparks to a greater extent in the malformed portions of myofibers, which is consistent with deficits in EC coupling control. In summary, our data show that aging mdx myofibers develop morphological malformations. These malformations are not associated with gross disruptions in cytoskeletal or t-tubule structure; however, alterations in myofiber Ca2+ signaling are evident.