INSERM U-769, Faculté de Pharmacie, Université de Paris Sud, 92296 Châtenay-Malabry, France.
Circulation. 2012 Jul 24;126(4):392-401. doi: 10.1161/CIRCULATIONAHA.111.075382. Epub 2012 Jun 18.
Catecholaminergic polymorphic ventricular tachycardia is characterized by stress-triggered syncope and sudden death. Patients with catecholaminergic polymorphic ventricular tachycardia manifest sinoatrial node (SAN) dysfunction, the mechanisms of which remain unexplored.
We investigated SAN Ca(2+) handling in mice carrying the catecholaminergic polymorphic ventricular tachycardia-linked mutation of ryanodine receptor (RyR2(R4496C)) and their wild-type (WT) littermates. In vivo telemetric recordings showed impaired SAN automaticity in RyR2(R4496C) mice after isoproterenol injection, analogous to what was observed in catecholaminergic polymorphic ventricular tachycardia patients after exercise. Pacemaker activity was explored by measuring spontaneous Ca(2+) transients in SAN cells within the intact SAN by confocal microscopy. RyR2(R4496C) SAN presented significantly slower pacemaker activity and impaired chronotropic response under β-adrenergic stimulation, accompanied by the appearance of pauses (in spontaneous Ca(2+) transients and action potentials) in 75% of the cases. Ca(2+) spark frequency was increased by 2-fold in RyR2(R4496C) SAN. Whole-cell patch-clamp experiments performed on isolated RyR2(R4496C) SAN cells showed that L-type Ca(2+) current (I(Ca,L)) density was reduced by ≈50%, an effect blunted by internal Ca(2+) buffering. Isoproterenol dramatically increased the frequency of Ca(2+) sparks and waves by ≈5 and ≈10-fold, respectively. Interestingly, the sarcoplasmic reticulum Ca(2+) content was significantly reduced in RyR2(R4496C) SAN cells in the presence of isoproterenol, which may contribute to stopping the "Ca(2+) clock" rhythm generation, originating SAN pauses.
The increased activity of RyR2(R4496C) in SAN leads to an unanticipated decrease in SAN automaticity by a Ca(2+)-dependent decrease of I(Ca,L) and sarcoplasmic reticulum Ca(2+) depletion during diastole, identifying subcellular pathophysiological alterations contributing to the SAN dysfunction in catecholaminergic polymorphic ventricular tachycardia patients.
儿茶酚胺多形性室性心动过速的特征是应激引发的晕厥和猝死。儿茶酚胺多形性室性心动过速患者表现出窦房结（SAN）功能障碍，但其机制尚不清楚。
我们研究了携带儿茶酚胺多形性室性心动过速相关突变的兰尼碱受体（RyR2(R4496C)）和其野生型（WT）同窝仔鼠的 SAN Ca(2+) 处理。在体内遥测记录中，我们发现异丙肾上腺素注射后 RyR2(R4496C) 小鼠的 SAN 自动性受损，类似于儿茶酚胺多形性室性心动过速患者运动后的情况。通过共聚焦显微镜测量完整 SAN 内 SAN 细胞内自发 Ca(2+) 瞬变，来探索起搏器活动。RyR2(R4496C) SAN 的起搏活动明显较慢，在β肾上腺素刺激下的变时反应受损，同时 75%的情况下出现暂停（自发 Ca(2+) 瞬变和动作电位）。RyR2(R4496C) SAN 的 Ca(2+) 火花频率增加了 2 倍。在分离的 RyR2(R4496C) SAN 细胞上进行的全细胞膜片钳实验表明，L 型 Ca(2+) 电流（I(Ca,L)）密度降低了约 50%，而内部 Ca(2+) 缓冲可减轻这种作用。异丙肾上腺素可分别使 Ca(2+) 火花和波的频率增加约 5 倍和 10 倍。有趣的是，在异丙肾上腺素存在的情况下，RyR2(R4496C) SAN 细胞的肌浆网 Ca(2+) 含量显著降低，这可能有助于停止 SAN 暂停的“Ca(2+) 时钟”节律生成。
SAN 中 RyR2(R4496C) 的活性增加，导致 SAN 自动性出乎意料地降低，这是由于舒张期 Ca(2+) 依赖性 I(Ca,L) 和肌浆网 Ca(2+) 耗竭所致，确定了导致儿茶酚胺多形性室性心动过速患者 SAN 功能障碍的亚细胞病理生理改变。
