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

• DOI: 10.1073/pnas.0913760107
• Publication Date: 2010-03-02T04:55:41Z
• Authors: Olha M. Koval; Xiaoquan Guan; Yuejin Wu; Mei-ling Joiner; Zhan Gao; Biyi Chen; Isabella M. Grumbach; Elizabeth D. Luczak; Roger J. Colbran; Long-Sheng Song; Thomas J. Hund; Peter J. Mohler; Mark E. Anderson
• Keywords: 0301 basic medicine; Binding Sites; Calcium Channels, L-Type; Cell Death; Cell Membrane; Action Potentials; Models, Biological; 3. Good health; Enzyme Activation; Protein Subunits; Sarcoplasmic Reticulum; Structure-Activity Relationship; 03 medical and health sciences; Leucine; Animals; Calcium; Mutant Proteins; Myocytes, Cardiac; Rabbits; Phosphorylation; Calcium-Calmodulin-Dependent Protein Kinase Type 2; Ion Channel Gating; Protein Binding

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 Ca2+channel (CaV1.2) activity, and enhanced expression of a specific CaV1.2 β-subunit protein isoform (β2a). We recently identified CaV1.2β2aresidues 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 WTβ2aexpression causes cellular Ca2+overload, arrhythmia-triggering cell membrane potential oscillations called early afterdepolarizations (EADs), and premature death in paced adult rabbit ventricular myocytes. Prevention of intracellular Ca2+release by ryanodine or global cellular CaMKII inhibition reduced EADs and improved cell survival to control levels in WTβ2a-expressing ventricular myocytes. In contrast, expression ofβ2aT498A or L493A mutants mimicked the protective effects of ryanodine or global cellular CaMKII inhibition by reducing Ca2+entry through CaV1.2 and inhibiting EADs. Furthermore, CaV1.2 currents recorded from cells overexpressing CaMKII phosphorylation- or binding-incompetentβ2asubunits were incapable of entering a CaMKII-dependent high-activity gating mode (mode 2), indicating thatβ2aThr 498 and Leu 493 are required for CaV1.2 activation by CaMKII in native cells. These data show that CaMKII binding and phosphorylation sites onβ2aare concise but pivotal components of a molecular and biophysical and mechanism for EADs and impaired survival in adult cardiomyocytes.