RYR2 and catecholaminergic polymorphic ventricular tachycardia: Firstly, Ca2+ sparks and other release events became significantly longer and highly recurrent in CPVT CMs during isoproterenol treatment compared with the brief and sporadic nature of Ca2+ sparks in controls, suggesting a disruption in the random activation of RyR2 channels and potentially elevated CICR gain (Zhang et al., 2013).