The oxidation‐resistant CaMKII‐MM281/282VV mutation does not prevent arrhythmias in CPVT1

Catecholaminergic polymorphic ventricular tachycardia type 1 (CPVT1) is an inherited arrhythmogenic disorder caused by missense mutations in the cardiac ryanodine receptors (RyR2), that result in increased β‐adrenoceptor stimulation‐induced diastolic Ca(2+) leak. We have previously shown that exercise training prevents arrhythmias in CPVT1, potentially by reducing the oxidation of Ca(2+)/calmodulin‐dependent protein kinase type II (CaMKII). Therefore, we tested whether an oxidation‐resistant form of CaMKII protects mice carrying the CPVT1‐causative mutation RyR2‐R2474S (RyR2‐RS) against arrhythmias. Antioxidant treatment (N‐acetyl‐L‐cysteine) reduced the frequency of β‐adrenoceptor stimulation‐induced arrhythmogenic Ca(2+) waves in isolated cardiomyocytes from RyR2‐RS mice. To test whether the prevention of CaMKII oxidation exerts an antiarrhythmic effect, mice expressing the oxidation‐resistant CaMKII‐MM281/282VV variant (MMVV) were crossed with RyR2‐RS mice to create a double transgenic model (RyR2‐RS/MMVV). Wild‐type mice served as controls. Telemetric ECG surveillance revealed an increased incidence of ventricular tachycardia and an increased arrhythmia score in both RyR2‐RS and RyR2‐RS/MMVV compared to wild‐type mice, both following a β‐adrenoceptor challenge (isoprenaline i.p.), and following treadmill exercise combined with a β‐adrenoceptor challenge. There were no differences in the incidence of arrhythmias between RyR2‐RS and RyR2‐RS/MMVV mice. Furthermore, no differences were observed in β‐adrenoceptor stimulation‐induced Ca(2+) waves in RyR2‐RS/MMVV compared to RyR2‐RS. In conclusion, antioxidant treatment reduces β‐adrenoceptor stimulation‐induced Ca(2+) waves in RyR2‐RS cardiomyocytes. However, oxidation‐resistant CaMKII‐MM281/282VV does not protect RyR2‐RS mice from β‐adrenoceptor stimulation‐induced Ca(2+) waves or arrhythmias. Hence, alternative oxidation‐sensitive targets need to be considered to explain the beneficial effect of antioxidant treatment on Ca(2+) waves in cardiomyocytes from RyR2‐RS mice.