Jiang Dawei, Chen Wenqian, Wang Ruiwu, Zhang Lin, Chen S R Wayne
Department of Physiology and Biophysics, University of Calgary, Calgary, AB, Canada.
Proc Natl Acad Sci U S A. 2007 Nov 13;104(46):18309-14. doi: 10.1073/pnas.0706573104. Epub 2007 Nov 1.
Different forms of ventricular arrhythmias have been linked to mutations in the cardiac ryanodine receptor (RyR)2, but the molecular basis for this phenotypic heterogeneity is unknown. We have recently demonstrated that an enhanced sensitivity to luminal Ca(2+) and an increased propensity for spontaneous Ca(2+) release or store-overload-induced Ca(2+) release (SOICR) are common defects of RyR2 mutations associated with catecholaminergic polymorphic or bidirectional ventricular tachycardia. Here, we investigated the properties of a unique RyR2 mutation associated with catecholaminergic idiopathic ventricular fibrillation, A4860G. Single-channel analyses revealed that, unlike all other disease-linked RyR2 mutations characterized previously, the A4860G mutation diminished the response of RyR2 to activation by luminal Ca(2+), but had little effect on the sensitivity of the channel to activation by cytosolic Ca(2+). This specific impact of the A4860G mutation indicates that the luminal Ca(2+) activation of RyR2 is distinct from its cytosolic Ca(2+) activation. Stable, inducible HEK293 cells expressing the A4860G mutant showed caffeine-induced Ca(2+) release but exhibited no SOICR. Importantly, HL-1 cardiac cells transfected with the A4860G mutant displayed attenuated SOICR activity compared with cells transfected with RyR2 WT. These observations provide the first evidence that a loss of luminal Ca(2+) activation and SOICR activity can cause ventricular fibrillation and sudden death. These findings also indicate that although suppressing enhanced SOICR is a promising antiarrhythmic strategy, its oversuppression can also lead to arrhythmias.
不同形式的室性心律失常与心脏雷诺丁受体（RyR）2的突变有关，但这种表型异质性的分子基础尚不清楚。我们最近证明，对管腔Ca(2+)的敏感性增强以及自发Ca(2+)释放或储存过载诱导的Ca(2+)释放（SOICR）倾向增加是与儿茶酚胺能多形性或双向室性心动过速相关的RyR2突变的常见缺陷。在此，我们研究了与儿茶酚胺能特发性心室颤动相关的独特RyR2突变A4860G的特性。单通道分析显示，与先前表征的所有其他与疾病相关的RyR2突变不同，A4860G突变降低了RyR2对管腔Ca(2+)激活的反应，但对通道对胞质Ca(2+)激活的敏感性影响很小。A4860G突变的这种特定影响表明，RyR2的管腔Ca(2+)激活与其胞质Ca(2+)激活不同。表达A4860G突变体的稳定、可诱导的HEK293细胞表现出咖啡因诱导的Ca(2+)释放，但未表现出SOICR。重要的是，与转染RyR2野生型的细胞相比，转染A4860G突变体的HL-1心脏细胞显示出减弱的SOICR活性。这些观察结果提供了首个证据，即管腔Ca(2+)激活和SOICR活性丧失可导致心室颤动和猝死。这些发现还表明，尽管抑制增强的SOICR是一种有前景的抗心律失常策略，但其过度抑制也可导致心律失常。
