CaV1.2 beta-subunit coordinates CaMKII-triggered cardiomyocyte death and afterdepolarizations

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 β-subunit protein isoform ( β 2a ). We recently identified Ca V 1.2 β 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 β 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 β 2a -expressing ventricular myocytes. In contrast, expression of β 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 β 2a subunits were incapable of entering a CaMKII-dependent high-activity gating mode (mode 2), indicating that β 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 β 2a are concise but pivotal components of a molecular and biophysical and mechanism for EADs and impaired survival in adult cardiomyocytes.