In conditions with abnormally increased activity of the cardiac ryanodine receptor (RyR2), Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) can contribute to a further destabilization of RyR2 that results in triggered arrhythmias. Therefore, inhibition of CaMKII in such conditions has been suggested as a strategy to suppress RyR2 activity and arrhythmias. However, suppression of RyR2 activity can lead to the development of arrhythmogenic Ca²⁺ alternans. Aim: To test whether suppression of RyR2 activity caused by inhibition of CaMKII increases propensity for Ca²⁺ alternans. Methods and results: We studied spontaneous Ca²⁺-release events and Ca²⁺ alternans in isolated left ventricular cardiomyocytes from mice carrying the gain-of-function RyR2 mutation RyR2-R2474S and from wild-type mice. CaMKII inhibition by KN-93 effectively decreased the frequency of spontaneous Ca²⁺-release events in RyR2‑R2474S cardiomyocytes exposed to the β‑adrenoceptor agonist isoprenaline. However, KN-93-treated RyR2-R2474S cardiomyocytes also showed increased propensity for Ca²⁺ alternans and increased Ca²⁺ alternans ratio compared with both an inactive analog of KN‑93 and with vehicle-treated controls. This increased propensity for Ca²⁺ alternans was explained by prolongation of Ca²⁺-release refractoriness. Importantly, the increased propensity for Ca²⁺ alternans in KN‑93-treated RyR2-R2474S cardiomyocytes did not surpass that of wild-type. Conclusions: Inhibition of CaMKII efficiently reduces spontaneous Ca²⁺-release, but promotes Ca²⁺ alternans in RyR2-R2474S cardiomyocytes with a gain-of-function RyR2 mutation. The dominant effect in RyR2-R2474S is to reduce spontaneous Ca²⁺-release, which supports this intervention as a therapeutic strategy in this specific condition. However, future studies on CaMKII inhibition in conditions with increased propensity for Ca²⁺ alternans should include investigation of both phenomena.

中文翻译：

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CaMKII 抑制对来自具有功能获得性 RyR2 突变的小鼠心室心肌细胞的自发 Ca2+ 释放和 Ca2+ 交替产生双重影响

在心脏兰尼碱受体 (RyR2) 活性异常增加的情况下，Ca ²⁺ /钙调蛋白依赖性蛋白激酶 II (CaMKII) 会导致 RyR2 的进一步不稳定，从而导致触发心律失常。因此，已建议在此类条件下抑制 CaMKII 作为抑制 RyR2 活性和心律失常的策略。然而，抑制 RyR2 活性会导致发生致心律失常的 Ca ²⁺交替糖。目的：测试由抑制 CaMKII 引起的 RyR2 活性抑制是否会增加 Ca ²⁺交替糖的倾向。方法和结果：我们研究了自发 Ca ²⁺释放事件和 Ca ²⁺来自携带功能获得性 RyR2 突变 RyR2-R2474S 的小鼠和野生型小鼠的分离的左心室心肌细胞中的交替糖。KN-93 对 CaMKII 的抑制有效降低了暴露于 β-肾上腺素受体激动剂异丙肾上腺素的 RyR2-R2474S 心肌细胞中自发 Ca ²⁺释放事件的频率。然而，与 KN-93的无活性类似物和载体处理的对照相比，KN-93 处理的 RyR2-R2474S 心肌细胞也显示出增加的 Ca ²⁺交替糖倾向和增加的 Ca ²⁺交替糖比率。Ca ²⁺交替糖的这种增加的倾向是通过延长Ca ²⁺释放耐火度来解释的。重要的是，Ca ^{2+ 的}倾向增加KN-93 处理的 RyR2-R2474S 心肌细胞中的交替糖并没有超过野生型。结论：在具有功能获得性 RyR2 突变的 RyR2-R2474S 心肌细胞中，CaMKII 的抑制有效减少自发 Ca ²⁺释放，但促进 Ca ²⁺交替。RyR2-R2474S 的主要作用是减少自发的 Ca ²⁺释放，这支持将这种干预作为这种特定条件下的治疗策略。然而，未来在 Ca ²⁺交替糖倾向增加的条件下对 CaMKII 抑制的研究应该包括对这两种现象的研究。