CALM1 and catecholaminergic polymorphic ventricular tachycardia: Using radiolabelled ATP and mice heart lysate as a source of Ca2+/CaM kinase II (CaMKIIδ), phosphorylation levels of syntide-2 (CaMKIIδ substrate) were measured using WT and CPVT-associated CaM variants (SignaTECT, Promega).