CaMKII blockade, cardiac conduction, and arrhythmia.
CaMKII blockade, cardiac conduction, and arrhythmia.
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CaMKII 阻断、心脏传导和心律失常。
DOI：
10.1093/cvr/cvx199
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发表时间：
2017
影响因子：
10.8
通讯作者：
Zaitsev,AlexeyV
中科院分区：
文献类型：
--
作者：
Warren,Mark;Zaitsev,AlexeyV
我们饶有兴趣地阅读了Takanari等人1发表在Cardiovascular Research上的研究，尤其是考虑到报告的结果与我们自己最近的研究形成鲜明对比。2 Takanari et al. 1的报告探讨了急性和慢性抑制Ca 2 +/钙调蛋白依赖性蛋白激酶II（CaMKII）通路对心室传导的影响。在慢性环境中获得的结果在我们自己的研究中没有对应的结果，在此不予评论。在急性情况下，作者在接受左心室（LV）内膜和中层心肌冷冻消融的离体兔心脏中使用钙调蛋白阻滞剂W7（10μM），仅留下1 mm的存活心外膜下层。他们使用光学标测，根据在LV游离壁中心部位起搏期间获得的等时激动标测图估计纵向（CVL）和横向（CVT）传导速度（CV）。他们发现，W7使CVL和CVT分别显著增加6.0%和12.6%（起搏周期长度为800 ms），并通过程控刺激减少室性心动过速/颤动（VT/VF）的诱导。他们将这些传导的改善与W7引起的椎间盘中Cx43的增强定位联系起来。我们最近在离体（但其他方面完整）兔心脏中使用光学标测的研究表明，用2.75 μM KN 93（KN 93直接靶向CaMKII以抑制其活性）阻断CaMKII导致传导明显不均匀减慢，最大效应发生在右心室（RV）流出道（RVOT）或其附近。2右室流出道的易损区随后成为2：1传导阻滞、湍流传导和心室颤动（VF）起始的首选部位。2从右室流出道分离的兔心室肌细胞的动作电位上升速度（dV/dtmax）明显低于从左室分离的兔心室肌细胞，KN 93进一步降低了这两个部位的dV/dtmax。在KN 93的存在下，在突然缩短起搏周期长度后，RVOT心肌细胞比LV心肌细胞更容易发生2：1激活失败。我们的结论是，CaMKII阻滞抑制心室兴奋性，并可能由于加剧RVOT内在较低的兴奋性而导致心律失常，使其在引起去极化储备减少的条件下容易发生折返性心律失常。假设W7和KN 93的作用都是由于抑制钙调蛋白/CaMK II通路，Takanari等人的研究1和我们的研究得出了关于该通路在调节心脏传导中的作用的相反结论。然而，W7和KN 93应该具有相同效果的假设可能是不正确的。注意，虽然KN 93通过干扰其与钙调蛋白的结合来抑制CaMK II，但用W-7阻断钙调蛋白将抑制除CaMK II之外的其他下游钙调蛋白靶点。4此外，W7和KN 93都有脱靶效应。5-8另一方面，W7和KN 93的作用之间的一致性强烈表明，这两种作用都是由于阻断钙调蛋白/CaMK II通路。考虑到这一逻辑，我们使用W7而不是KN 93进行了实验，其他实验模型与我们以前的出版物相同。2简而言之，连续灌注（血氧正常）的兔心脏在窦性心律期间暴露于W7（10或20μM），并从放置在LV和RV中的电极以递增速率定期进行心室起搏。在没有机械解偶联剂的情况下，收集由电压敏感染料Di-4-ANEPPS染色心肌所发射的荧光。
We have read the study by Takanari et al. 1 published in Cardiovascular Research with interest, all the more so given that the reported results are in stark contrast with our own recent study. 2 The report by Takanari et al. 1 explored the effects of acute and chronic inhibition of the Ca2þ/calmodulin dependent protein kinase II (CaMKII) pathway on ventricular conduction. The results obtained in the chronic setting do not have a counterpart in our own study, and will not be commented here. In the acute setting, the authors used calmodulin blocker W7 (10μM) in isolated rabbit hearts subjected to cryoablation of the left ventricular (LV) endo-and midmyocardium, leaving only an $1 mm of viable subepicardial layer. They used optical mapping to estimate the longitudinal (CVL) and transverse (CVT) conduction velocity (CV) from isochronal activation maps obtained during pacing at a site in the centre of the LV free wall. They found that W7 significantly increased CVL and CVT by 6.0 and 12.6%, respectively (at the pacing cycle length of 800ms) and decreased inducibility of ventricular tachycardia/fibrillation (VT/VF) by programmed stimulation. They linked these improvements in conduction to augmented localization of Cx43 in the intercalated disc caused by W7. Our recent study using optical mapping in isolated (but otherwise intact) rabbit hearts has demonstrated that CaMKII blockade with 2.75 μM KN93 (KN93 directly targets CaMKII to inhibit its activity) resulted in a marked non-uniform slowing of conduction, with the largest effect occurring in or near the right ventricular (RV) outflow tract (RVOT). 2 The vulnerable region in the RVOT subsequently became a preferred location for 2: 1 conduction block, turbulent conduction, and initiation of VF upon subjecting the hearts to global ischemia. 2 Rabbit ventricular myocytes isolated from RVOT exhibited intrinsically lower action potential upstroke velocity (dV/dtmax) than those isolated from the LV, and KN93 further depressed dV/dtmax in both locations. In the presence of KN93, RVOT myocytes were much more prone to 2: 1 activation failure than LV myocytes after abrupt shortening of the pacing cycle length. We concluded that CaMKII blockade depresses ventricular excitability and is potentially proarrhythmic due to exacerbating intrinsically lower excitability in the RVOT, making it vulnerable to reentrant arrhythmias under conditions causing reduced depolarization reserve. Assuming that the effects of W7 and KN93 are both due to inhibition of calmodulin/CaMKII pathway, the study by Takanari et al. 1 and ours lead to opposite conclusions with regard to the role of this pathway in regulation of cardiac conduction. However, the assumption that W7 and KN93 should have the same effect could be incorrect. Note that whilst KN93 inhibits CaMKII by interfering with its binding to calmodulin, 3 blockade of calmodulin with W-7 will inhibit other downstream calmodulin targets besides CaMKII. 4 In addition, both W7 and KN93 have off-target effects. 5–8 On the other hand, concordance between the effects of W7 and KN93 would strongly suggest that both these effects are due to blocking calmodulin/CaMKII pathway. With this logic in mind, we performed experiments using W7 instead of KN93 in otherwise the same experimental model as in our previous publication. 2 Briefly, continuously perfused (normoxemic) rabbit hearts were exposed to W7 (10 or 20μM) during sinus rhythm, and periodically subject to ventricular pacing at incremental rates from electrodes placed in the LV and RV. In the absence of mechanical uncouplers, fluorescence emitted by the voltage sensitive dye Di-4-ANEPPS staining the myocardium was collected …