Excessive activation of calmodulin kinase II (CaMKII) causes arrhythmias and 
heart failure, but the cellular mechanisms for CaMKII-targeted proteins causing 
disordered cell membrane excitability and myocardial dysfunction remain 
uncertain. Failing human cardiomyocytes exhibit increased CaMKII and 
voltage-gated Ca(2+) channel (Ca(V)1.2) activity, and enhanced expression of a 
specific Ca(V)1.2 beta-subunit protein isoform (beta(2a)). We recently 
identified Ca(V)1.2 beta(2a) residues critical for CaMKII phosphorylation (Thr 
498) and binding (Leu 493), suggesting the hypothesis that these amino acids are 
crucial for cardiomyopathic consequences of CaMKII signaling. Here we show WT 
beta(2a) expression causes cellular Ca(2+) overload, arrhythmia-triggering cell 
membrane potential oscillations called early afterdepolarizations (EADs), and 
premature death in paced adult rabbit ventricular myocytes. Prevention of 
intracellular Ca(2+) release by ryanodine or global cellular CaMKII inhibition 
reduced EADs and improved cell survival to control levels in WT 
beta(2a)-expressing ventricular myocytes. In contrast, expression of beta(2a) 
T498A or L493A mutants mimicked the protective effects of ryanodine or global 
cellular CaMKII inhibition by reducing Ca(2+) entry through Ca(V)1.2 and 
inhibiting EADs. Furthermore, Ca(V)1.2 currents recorded from cells 
overexpressing CaMKII phosphorylation- or binding-incompetent beta(2a) subunits 
were incapable of entering a CaMKII-dependent high-activity gating mode (mode 
2), indicating that beta(2a) Thr 498 and Leu 493 are required for Ca(V)1.2 
activation by CaMKII in native cells. These data show that CaMKII binding and 
phosphorylation sites on beta(2a) are concise but pivotal components of a 
molecular and biophysical and mechanism for EADs and impaired survival in adult 
cardiomyocytes.