Functional Study of Sarcoglycan in Cardiomyopathic Muscle Cells

delta-sarcoglycan（肌营养不良蛋白-糖蛋白复合物的一种成分）的缺乏会导致BIO14.6仓鼠心肌病和骨骼肌营养不良。利用正常和BIO14.6仓鼠（30-40日龄）的肌肉培养肌管（培养2-4天），研究了δ肌聚糖参与钙代谢的可能性，并最终导致肌细胞损伤。免疫印迹分析显示，与细胞钙处理有关的l型钙通道、ryanodine受体、SR-CaATPase、Na/Ca交换器等膜蛋白含量在对照组和BI014.6肌管之间无显著差异。在静息条件下，Ca^<2+>内流进入BIO14.6肌管2+显著高于对照组（5分钟时高达1.8倍），表明Ca^<2+>内流在BIO14.6肌管中被激活。当这些细胞被置于高达20%的循环伸长1h时，仅在BIO14.6肌管中观察到肌酸磷酸激酶（CK）释放到培养基中的显著增加。100μM GdCl_3降低了^<45>Ca^<2+>内流和CK释放。使用2+腺病毒载体转染δ肌聚糖也可以挽救异常的钙代谢和CK释放。静息时肌管中钙内流的增加可能是由于在这些肌管中检测到的拉伸激活阳离子通道的基础活性增加，这些结果提示了这种肌营养不良动物模型中细胞损伤的可能机制。

Deficiency of delta-sarcoglycan, a component of the dystrophin-glycoprotein complex, causes cardiomyopathy and skeletal muscle dystrophy in BIO14.6 hamsters. Using cultured myotubes (for 2-4 days) prepared from muscle of normal and BIO14.6 hamsters (30-40 day old), we investigated the possibility that the delta-sarcoglycan in calcium metabolism which may ultimately leads to myocyte damage. Immunoblot analysis revealed that the contents of membrane proteins involved in cell Ca handling such as L-type Ca channel, ryanodine receptor, SR-CaATPase, Na/Ca exchanger were not different between control and BI014.6 myotubes. ^<45>Ca^<2+> influx into BIO14.6 myotubes 2+ under resting conditions was significantly higher (up to1.8-fold at 5 min) than in controls, suggesting that Ca^<2+> influx is activated in BIO 14.6 myotubes. When these cells were subjected to cyclic elongation of up to 20 % for 1h, a marked increase in creatine phosphokinase (CK) release into the medium was obsereved in only BIO14.6 myotubes. 100μM GdCl_3 reduced ^<45>Ca^<2+> influx and CK release. Transfection of delta sarcoglycan using 2+ adenovirus vector also rescue abnormal calcium metabolism and CK release The increased resting Ca influx in BIO14.6 myotubes may be due to the increased basal activity of stretch-activated cation channels detected in these myotubes and these results suggest a possible mechanism for cell damage in this animal model of muscular dystrophy.