Department of Laboratory Medicine, First Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan 450052, China.
Chin Med J (Engl). 2012 Mar;125(5):815-22.
Studies have shown that β-blockers can improve cardiac performance in heart failure (HF) by reversing protein kinase A (PKA)-mediated sarcoplasmic reticulum (SR) Ca2+ leak. However, it is being strongly questioned as to whether the PKA-mediated ryanodine receptor (RyR2) hyper-phosphorylation is a critical regulator of SR Ca2+ leak. In this study, we used a rabbit HF model to investigate whether β-blockers affect SR Ca2+ leak by other potential mechanisms.
New Zealand white rabbits were randomly divided in three groups (n=7 in each group): normal group, metoprolol-untreated group and metoprolol-treated group. Cardiac function was determined by echocardiography and hemodynamic assays. The SR Ca2+ leak was measured by a calcium-imaging device, and the expression and activities of related proteins were evaluated by Western blotting and auto-phosphorylation.
In the metoprolol-untreated group, there was significantly increased ventricular cavity size, reduced systolic function, increased SR Ca2+ leak, reduced associated amount of FK506 binding protein 12.6 (FKBP12.6), increased expression and activity of PKA and Ca2+/calmodulin-dependent protein kinase II (CaMKII), and increased phosphorylated RyR2 phosphorylation sites (with unchanged RyR2-P2030). In the treated group, there was partly increased ventricular cavity size with preserved systolic function, but no prominent Ca2+ leak, with unchanged expression and activity of PKA, CaMKII and their RyR2 phosphorylation sites.
Chronic administration of metoprolol prevented the SR Ca2+ leak by restoring not only PKA-dependent but also CaMKII-dependent hyper-phosphorylation of RyR2, which may be one of the potential mechanisms by which β-blockers improve cardiac function and reduce the incidence of fatal arrhythmia in HF.
研究表明，β受体阻滞剂通过逆转蛋白激酶 A（PKA）介导的肌浆网（SR）Ca2+泄漏，可改善心力衰竭（HF）患者的心功能。然而，PKA 介导的兰尼碱受体（RyR2）过度磷酸化是否是 SR Ca2+泄漏的关键调节因子，这一观点正受到强烈质疑。在本研究中，我们使用兔 HF 模型来探讨β受体阻滞剂是否通过其他潜在机制影响 SR Ca2+泄漏。
新西兰白兔随机分为三组（每组 n=7）：正常组、美托洛尔未处理组和美托洛尔处理组。通过超声心动图和血流动力学检测评估心功能，使用钙成像设备测量 SR Ca2+泄漏，通过 Western blot 和自动磷酸化检测评估相关蛋白的表达和活性。
在美托洛尔未处理组中，心室腔明显增大，收缩功能降低，SR Ca2+泄漏增加，FK506 结合蛋白 12.6（FKBP12.6）相关量减少，PKA 和钙/钙调蛋白依赖性蛋白激酶 II（CaMKII）表达和活性增加，RyR2 磷酸化位点（RyR2-P2030 不变）增加。在处理组中，心室腔部分增大，收缩功能保持不变，但 Ca2+泄漏不明显，PKA、CaMKII 及其 RyR2 磷酸化位点的表达和活性不变。
美托洛尔的慢性给药不仅通过恢复 PKA 依赖性，而且通过恢复 CaMKII 依赖性 RyR2 过度磷酸化来防止 SR Ca2+泄漏，这可能是β受体阻滞剂改善心功能和降低 HF 致命性心律失常发生率的潜在机制之一。
