Department of Physiology and Pharmacology, Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada.
Circ Res. 2013 Aug 16;113(5):517-26. doi: 10.1161/CIRCRESAHA.113.301678. Epub 2013 Jul 15.
Phospholamban (PLN) is an inhibitor of cardiac sarco(endo)plasmic reticulum Ca²⁺ ATPase. PLN knockout (PLN-KO) enhances sarcoplasmic reticulum Ca²⁺ load and Ca²⁺ leak. Conversely, PLN-KO accelerates Ca²⁺ sequestration and aborts arrhythmogenic spontaneous Ca²⁺ waves (SCWs). An important question is whether these seemingly paradoxical effects of PLN-KO exacerbate or protect against Ca²⁺-triggered arrhythmias.
We investigate the impact of PLN-KO on SCWs, triggered activities, and stress-induced ventricular tachyarrhythmias (VTs) in a mouse model of cardiac ryanodine-receptor (RyR2)-linked catecholaminergic polymorphic VT.
We generated a PLN-deficient, RyR2-mutant mouse model (PLN-/-/RyR2-R4496C+/-) by crossbreeding PLN-KO mice with catecholaminergic polymorphic VT-associated RyR2-R4496C mutant mice. Ca²⁺ imaging and patch-clamp recording revealed cell-wide propagating SCWs and triggered activities in RyR2-R4496C+/- ventricular myocytes during sarcoplasmic reticulum Ca²⁺ overload. PLN-KO fragmented these cell-wide SCWs into mini-waves and Ca²⁺ sparks and suppressed the triggered activities evoked by sarcoplasmic reticulum Ca²⁺ overload. Importantly, these effects of PLN-KO were reverted by partially inhibiting sarco(endo)plasmic reticulum Ca²⁺ ATPase with 2,5-di-tert-butylhydroquinone. However, Bay K, caffeine, or Li⁺ failed to convert mini-waves to cell-wide SCWs in PLN-/-/RyR2-R4496C+/- ventricular myocytes. Furthermore, ECG analysis showed that PLN-KO mice are not susceptible to stress-induced VTs. On the contrary, PLN-KO protected RyR2-R4496C mutant mice from stress-induced VTs.
Our results demonstrate that despite severe sarcoplasmic reticulum Ca²⁺ leak, PLN-KO suppresses triggered activities and stress-induced VTs in a mouse model of catecholaminergic polymorphic VT. These data suggest that breaking up cell-wide propagating SCWs by enhancing Ca²⁺ sequestration represents an effective approach for suppressing Ca²⁺-triggered arrhythmias.
磷蛋白（PLN）是心肌肌浆网 Ca²⁺-ATP 酶的抑制剂。PLN 敲除（PLN-KO）增强肌浆网 Ca²⁺负荷和 Ca²⁺渗漏。相反，PLN-KO 加速 Ca²⁺摄取并终止致心律失常性自发性 Ca²⁺波（SCWs）。一个重要的问题是，PLN-KO 的这些看似矛盾的作用是加重还是保护 Ca²⁺触发的心律失常。
我们研究了 PLN-KO 对心脏兰尼碱受体（RyR2）相关儿茶酚胺多形性 VT 小鼠模型中 SCWs、触发活动和应激诱导的室性心动过速（VTs）的影响。
我们通过将 PLN-KO 小鼠与儿茶酚胺多形性 VT 相关的 RyR2-R4496C 突变小鼠杂交，生成了 PLN 缺陷、RyR2 突变小鼠模型（PLN-/-/RyR2-R4496C+/-）。Ca²⁺成像和膜片钳记录显示，在 RyR2-R4496C+/- 心室肌细胞中，肌浆网 Ca²⁺过载时会发生全细胞传播的 SCWs 和触发活动。PLN-KO 将这些全细胞 SCWs 分割成微小波和 Ca²⁺火花，并抑制肌浆网 Ca²⁺过载引发的触发活动。重要的是，用 2,5-二叔丁基对苯二酚部分抑制肌浆网 Ca²⁺-ATP 酶可逆转 PLN-KO 的这些作用。然而，Bay K、咖啡因或 Li⁺未能将微小波转化为 PLN-/-/RyR2-R4496C+/- 心室肌细胞中的全细胞 SCWs。此外，心电图分析表明 PLN-KO 小鼠不易发生应激诱导的 VT。相反，PLN-KO 保护 RyR2-R4496C 突变小鼠免受应激诱导的 VT。
我们的结果表明，尽管肌浆网 Ca²⁺渗漏严重，但 PLN-KO 仍能抑制儿茶酚胺多形性 VT 小鼠模型中的触发活动和应激诱导的 VT。这些数据表明，通过增强 Ca²⁺摄取来打断全细胞传播的 SCWs 是抑制 Ca²⁺触发心律失常的有效方法。
