骨骼肌收缩是由兴奋收缩(EC)耦合过程中释放的Ca2增加引起的,EC偶联缺陷与人肌病有关。EC偶联需要横向小管膜中的电压感应二氢吡啶受体(DHPR)与肌浆网(SR)中的Ca2释放通道ryanodine受体1(RyR1)之间的通讯。Stac3蛋白(SH3和富含半胱氨酸的结构域3)是EC偶联装置的重要组成部分,人类STAC3中的突变会导致使人衰弱的美洲原住民肌病(NAM),但Stac3如何作用于DHPR和/或RyR1的性质是未知的。使用电子显微镜,电生理学,和斑马鱼肌纤维的动态成像,我们发现DHPR水平显著降低,功能,和stac3突变体的稳定性。此外,在没有咖啡因敏感性改变的情况下,stac3NAM肌纤维在广泛的浓度范围内表现出咖啡因诱导的Ca2+释放增加以及内部存储中的Ca2+增加,这与增加的SR腔Ca2+一致。这些发现定义了Stac3在EC偶联和人类疾病中的关键作用。
Skeletal muscle contractions are initiated by an increase in Ca2+ released during excitation-contraction (EC) coupling, and defects in EC coupling are associated with human myopathies. EC coupling requires communication between voltage-sensing dihydropyridine receptors (DHPRs) in transverse tubule membrane and Ca2+ release channel ryanodine receptor 1 (RyR1) in the sarcoplasmic reticulum (SR). Stac3 protein (SH3 and cysteine-rich domain 3) is an essential component of the EC coupling apparatus and a mutation in human STAC3 causes the debilitating Native American myopathy (NAM), but the nature of how Stac3 acts on the DHPR and/or RyR1 is unknown. Using electron microscopy, electrophysiology, and dynamic imaging of zebrafish muscle fibers, we find significantly reduced DHPR levels, functionality, and stability in stac3 mutants. Furthermore, stac3NAM myofibers exhibited increased caffeine-induced Ca2+ release across a wide range of concentrations in the absence of altered caffeine sensitivity as well as increased Ca2+ in internal stores, which is consistent with increased SR luminal Ca2+ These findings define critical roles for Stac3 in EC coupling and human disease.