PDF(Pubmed)
Abstract：
Ryanodine receptor 2 (RyR2) is an ion channel in the heart responsible for releasing into the cytosol most of the Ca2+ required for contraction. Proper regulation of RyR2 is critical, as highlighted by the association between channel dysfunction and cardiac arrhythmia. Lower RyR2 expression is also observed in some forms of heart disease; however, there is limited information on the impact of this change on excitation-contraction (e-c) coupling, Ca2+-dependent arrhythmias, and cardiac performance. We used a constitutive knock-out of RyR2 in rabbits (RyR2-KO) to assess the extent to which a stable decrease in RyR2 expression modulates Ca2+ handling in the heart. We found that homozygous knock-out of RyR2 in rabbits is embryonic lethal. Remarkably, heterozygotes (KO+/-) show ~50% loss of RyR2 protein without developing an overt phenotype at the intact animal and whole heart levels. Instead, we found that KO+/- myocytes show (1) remodeling of RyR2 clusters, favoring smaller groups in which channels are more densely arranged; (2) lower Ca2+ spark frequency and amplitude; (3) slower rate of Ca2+ release and mild but significant desynchronization of the Ca2+ transient; and (4) a significant decrease in the basal phosphorylation of S2031, likely due to increased association between RyR2 and PP2A. Our data show that RyR2 deficiency, although remarkable at the molecular and subcellular level, has only a modest impact on global Ca2+ release and is fully compensated at the whole-heart level. This highlights the redundancy of RyR2 protein expression and the plasticity of the e-c coupling apparatus.
摘要：
Ryanodine受体2（RyR2）是心脏中的离子通道，负责将收缩所需的大部分Ca2释放到细胞质中。对RyR2的适当调节至关重要，正如通道功能障碍与心律失常之间的关联所强调的那样。在某些形式的心脏病中也观察到较低的RyR2表达;然而，关于这种变化对激励-收缩(e-c)耦合的影响的信息有限，Ca2+依赖性心律失常，和心脏性能。我们在兔子中使用RyR2的组成型敲除（RyR2-KO）来评估RyR2表达的稳定降低调节心脏中Ca2处理的程度。我们发现兔子中RyR2的纯合敲除是胚胎致死的。值得注意的是,杂合子（KO/-）显示RyR2蛋白的〜50％损失，而在完整的动物和整个心脏水平上没有明显的表型。相反，我们发现KO+/-心肌细胞表现出(1)RyR2簇的重塑，有利于通道排列更密集的较小组；（2）较低的Ca2火花频率和振幅；（3）Ca2释放速率较慢，Ca2瞬时的轻度但显着去同步化；（4）S2031的基础磷酸化显着降低，可能是由于RyR2和PP2A之间的关联增加。我们的数据显示RyR2缺乏症，尽管在分子和亚细胞水平上非常显著，对全球Ca2+释放只有适度的影响，并且在整个心脏水平上得到完全补偿。这突出了RyR2蛋白表达的冗余和e-c偶联装置的可塑性。
