PDF(Pubmed)
Abstract：
Physiological muscle contraction requires an intact ligand gating mechanism of the ryanodine receptor 1 (RyR1), the Ca2+-release channel of the sarcoplasmic reticulum. Some mutations impair the gating and thus cause muscle disease. The RyR1 mutation T4706M is linked to a myopathy characterized by muscle weakness. Although, low expression of the T4706M RyR1 protein can explain in part the symptoms, little is known about the function RyR1 channels with this mutation. In order to learn whether this mutation alters channel function in a manner that can account for the observed symptoms, we examined RyR1 channels isolated from mice homozygous for the T4709M (TM) mutation at the single channel level. Ligands, including Ca2+, ATP, Mg2+ and the RyR inhibitor dantrolene were tested. The full conductance of the TM channel was the same as that of wild type (wt) channels and a population of partial open (subconductive) states were not observed. However, two unique sub-populations of TM RyRs were identified. One half of the TM channels exhibited high open probability at low (100 nM) and high (50 μM) cytoplasmic [Ca2+], resulting in Ca2+-insensitive, constitutively high Po channels. The rest of the TM channels exhibited significantly lower activity within the physiologically relevant range of cytoplasmic [Ca2+], compared to wt. TM channels retained normal Mg2+ block, modulation by ATP, and inhibition by dantrolene. Together, these results suggest that the TM mutation results in a combination of primary and secondary RyR1 dysfunctions that contribute to disease pathogenesis.
摘要：
生理性肌肉收缩需要ryanodine受体1（RyR1）的完整配体门控机制，肌浆网的Ca2+释放通道。一些突变损害门控并因此引起肌肉疾病。RyR1突变T4706M与以肌肉无力为特征的肌病有关。虽然,T4706MRyR1蛋白的低表达可以解释部分症状，对具有这种突变的RyR1通道的功能知之甚少。为了了解这种突变是否以可以解释观察到的症状的方式改变通道功能，我们在单通道水平检查了从T4709M(TM)突变纯合小鼠分离的RyR1通道。配体,包括Ca2+，ATP,测试了Mg2+和RyR抑制剂丹曲林。TM通道的全电导与野生型（wt）通道相同，未观察到部分开放（亚导电）状态。然而,确定了两个独特的TMRyRs亚群。一半的TM通道在低（100nM）和高（50μM）细胞质[Ca2]显示出高开放概率，导致Ca2+不敏感，组成较高的Po通道。其余的TM通道在细胞质[Ca2]的生理相关范围内表现出明显较低的活性，与wt相比。TM通道保持正常的Mg2+阻滞，通过ATP调节，和丹曲林的抑制作用。一起,这些结果表明，TM突变导致原发性和继发性RyR1功能障碍的组合，这有助于疾病的发病机理。
