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 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.
Koval
Olha M
OM
Department of Internal Medicine, University of Iowa, 2256 Carver Biomedical Research Building, Iowa City, IA 52242, USA.
Guan
Xiaoquan
X
Wu
Yuejin
Y
Joiner
Mei-Ling
ML
Gao
Zhan
Z
Chen
Biyi
B
Grumbach
Isabella M
IM
Luczak
Elizabeth D
ED
Colbran
Roger J
RJ
Song
Long-Sheng
LS
Hund
Thomas J
TJ
Mohler
Peter J
PJ
Anderson
Mark E
ME
D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000378:metabolism*; D016923:Cell Death; D002462:Cell Membrane / Q000378:metabolism; D004789:Enzyme Activation; D015640:Ion Channel Gating; D007930:Leucine / Q000378:metabolism; D008954:Models, Biological; D050505:Mutant Proteins / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000166:cytology* / Q000201:enzymology*; D010766:Phosphorylation; D011485:Protein Binding; D021122:Protein Subunits / Q000378:metabolism*; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D013329:Structure-Activity Relationship; D013912:Threonine / Q000378:metabolism
D020746:Calcium Channels, L-Type; D050505:Mutant Proteins; D021122:Protein Subunits; D013912:Threonine; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D007930:Leucine; D002118:Calcium