Department of Physiology, University of Bern, Buehlplatz 5, Bern 3012, Switzerland.
Am J Physiol Heart Circ Physiol. 2009 Dec;297(6):H1992-2003. doi: 10.1152/ajpheart.00602.2009. Epub 2009 Sep 25.
Duchenne muscular dystrophy represents a severe inherited disease of striated muscle. It is caused by a mutation of the dystrophin gene and characterized by a progressive loss of skeletal muscle function. Most patients also develop a dystrophic cardiomyopathy, resulting in dilated hypertrophy and heart failure, but the cellular mechanisms leading to the deterioration of cardiac function remain elusive. In the present study, we tested whether defective excitation-contraction (E-C) coupling contributes to impaired cardiac performance. "E-C coupling gain" was determined in cardiomyocytes from control and dystrophin-deficient mdx mice. To this end, L-type Ca2+ currents (ICaL) were measured with the whole cell patch-clamp technique, whereas Ca2+ transients were simultaneously recorded with confocal imaging of fluo-3. Initial findings indicated subtle changes of E-C coupling in mdx cells despite matched Ca2+ loading of the sarcoplasmic reticulum (SR). However, lowering the extracellular Ca2+ concentration, a maneuver used to unmask latent E-C coupling problems, was surprisingly much better tolerated by mdx myocytes, suggesting a hypersensitive E-C coupling mechanism. Challenging the SR Ca2+ release by slow elevations of the intracellular Ca2+ concentration resulted in Ca2+ oscillations after a much shorter delay in mdx cells. This is consistent with an enhanced Ca2+ sensitivity of the SR Ca2+-release channels [ryanodine receptors (RyRs)]. The hypersensitivity could be normalized by the introduction of reducing agents, indicating that the elevated cellular ROS generation in dystrophy underlies the abnormal RyR sensitivity and hypersensitive E-C coupling. Our data suggest that in dystrophin-deficient cardiomyocytes, E-C coupling is altered due to potentially arrhythmogenic changes in the Ca2+ sensitivity of redox-modified RyRs.
杜氏肌营养不良症是一种严重的遗传性肌肉疾病。它是由肌营养不良蛋白基因突变引起的，其特征是骨骼肌功能进行性丧失。大多数患者还会发展出肌营养不良性心肌病，导致扩张性肥大和心力衰竭，但导致心脏功能恶化的细胞机制仍不清楚。在本研究中，我们测试了是否有缺陷的兴奋-收缩（E-C）偶联导致心脏功能受损。通过全细胞膜片钳技术测量了来自对照和肌营养不良蛋白缺陷型 mdx 小鼠的心肌细胞中的 L 型 Ca2+电流（ICaL），同时通过共聚焦显微镜对 fluo-3 的钙瞬变进行同步记录。初步研究结果表明，尽管肌浆网（SR）的 Ca2+加载匹配，但 mdx 细胞的 E-C 偶联仍有细微变化。然而，令人惊讶的是，降低细胞外 Ca2+浓度（一种用于揭示潜在 E-C 偶联问题的操作）对 mdx 心肌细胞的耐受性要好得多，这表明存在敏感的 E-C 偶联机制。通过缓慢升高细胞内 Ca2+浓度来挑战 SR Ca2+释放，导致 mdx 细胞中的 Ca2+振荡延迟更短。这与 SR Ca2+释放通道[ryanodine 受体（RyRs）]的 Ca2+敏感性增强一致。还原剂的引入可使超敏性正常化，表明在肌营养不良症中升高的细胞内 ROS 生成是 RyR 敏感性异常和敏感的 E-C 偶联的基础。我们的数据表明，在肌营养不良蛋白缺陷型心肌细胞中，由于氧化还原修饰的 RyR 的 Ca2+敏感性的潜在心律失常变化，E-C 偶联发生改变。
