Department of Physiology and Pharmacology, the Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, AB, Canada.
Circ Res. 2012 Mar 30;110(7):968-77. doi: 10.1161/CIRCRESAHA.111.256560. Epub 2012 Feb 28.
Naturally occurring mutations in the cardiac ryanodine receptor (RyR2) have been associated with both cardiac arrhythmias and cardiomyopathies. It is clear that delayed afterdepolarization resulting from abnormal activation of sarcoplasmic reticulum Ca2+ release is the primary cause of RyR2-associated cardiac arrhythmias. However, the mechanism underlying RyR2-associated cardiomyopathies is completely unknown.
In the present study, we investigate the role of the NH2-terminal region of RyR2 in and the impact of a number of cardiomyopathy-associated RyR2 mutations on the termination of Ca2+ release.
The 35-residue exon-3 region of RyR2 is associated with dilated cardiomyopathy. Single-cell luminal Ca2+ imaging revealed that the deletion of the first 305 NH2-terminal residues encompassing exon-3 or the deletion of exon-3 itself markedly reduced the luminal Ca2+ threshold at which Ca2+ release terminates and increased the fractional Ca2+ release. Single-cell cytosolic Ca2+ imaging also showed that both RyR2 deletions enhanced the amplitude of store overload-induced Ca2+ transients in HEK293 cells or HL-1 cardiac cells. Furthermore, the RyR2 NH2-terminal mutations, A77V, R176Q/T2504M, R420W, and L433P, which are associated with arrhythmogenic right ventricular displasia type 2, also reduced the threshold for Ca2+ release termination and increased fractional release. The RyR2 A1107M mutation associated with hypertrophic cardiomyopathy had the opposite action (i.e., increased the threshold for Ca2+ release termination and reduced fractional release).
These results provide the first evidence that the NH2-terminal region of RyR2 is an important determinant of Ca2+ release termination, and that abnormal fractional Ca2+ release attributable to aberrant termination of Ca2+ release is a common defect in RyR2-associated cardiomyopathies.
心脏兰尼碱受体（RyR2）的自然突变与心律失常和心肌病都有关。显然，由于肌浆网 Ca2+释放异常激活导致的延迟后除极是 RyR2 相关心律失常的主要原因。然而，RyR2 相关心肌病的发病机制尚不清楚。
本研究旨在探讨 RyR2 的 NH2 端区域在 Ca2+释放终止中的作用，以及多种与心肌病相关的 RyR2 突变对 Ca2+释放终止的影响。
RyR2 的 35 个残基外显子 3 区与扩张型心肌病有关。单细胞管腔 Ca2+成像显示，缺失前 305 个 NH2 端残基（包括外显子 3）或缺失外显子 3 本身，显著降低了 Ca2+释放终止的管腔 Ca2+阈值，并增加了 Ca2+释放分数。单细胞胞浆 Ca2+成像还显示，RyR2 缺失均增强了 HEK293 细胞或 HL-1 心脏细胞中储存超负荷诱导的 Ca2+瞬变的幅度。此外，与心律失常性右室发育不良 2 型相关的 RyR2 NH2 端突变 A77V、R176Q/T2504M、R420W 和 L433P，也降低了 Ca2+释放终止的阈值，并增加了释放分数。与肥厚型心肌病相关的 RyR2 A1107M 突变则有相反的作用（即增加 Ca2+释放终止的阈值并降低释放分数）。
这些结果首次证明 RyR2 的 NH2 端区域是 Ca2+释放终止的重要决定因素，异常的 Ca2+释放分数归因于 Ca2+释放终止异常，是 RyR2 相关心肌病的共同缺陷。
