Abstract 14642: Calcium Calmodulin Dependent Protein Kinase II Overexpression Predisposes Myocytes to Isoproterenol-Induced Early Afterdepolarizations Before the Onset of Heart Failure
BACKGROUND: Hyperactivity of Ca2+-Calmodulin dependent protein kinase II (CaMKII) occurs in human HF, and transgenic mice expressing CaMKIIδc (CaMKIIδc TG) exhibit afterdepolarizations and triggered arrhythmias. Thus, CaMKII hyperactivity may contribute to HF sudden death. Two key questions regarding CaMKIIδc-mediated arrhythmogenesis are: (1) How does CaMKII promote arrhythmia at various stages of HF progression? (2) How does βAR stimulation interact with CaMKII signaling to exacerbate arrhythmogenesis? We studied these questions in CaMKIIδc TG myocytes, and with computational models modified to represent the transgenic cell.
METHODS: Ventricular myocytes were isolated, prior to onset of HF symptoms, from cardiac-specific CaMKIIδc TG mice (TG, n = 9), and WT littermates (n = 7). Cellular instability was examined by pacing (1 Hz) in ruptured patch current clamp, with simultaneous fura-2 epifluorescence, and in the presence and absence of 100 nM Isoproterenol (Iso). A published mouse myocyte model was modified to recapitulate CaMKII- and PKA-mediated alterations to key ion currents and Ca2+-handling.
RESULTS: In the absence of Iso, afterdepolarizations were virtually nonexistent (4 events in 1775 cycles). Iso elicited EADs in TG (5/11 cells, 25% of cycles) but not WT myocytes (1/9 cells; 2.5 % of cycles; p < 0.05), and this was associated with greater Iso-induced AP prolongation (prior to EAD appearance) in TG (14.4 ± 5.3 ms) vs. WT (5.8 ± 2.8 ms; p < 0.05). DADs were not observed in any condition. CaMKIIδc TG did not impact global Ca2+ transients in these pre-HF cells (p > 0.05), while Iso elicited established Ca2+-handling effects in both groups. Simulations captured the observed AP prolongation and EAD genesis, and only when the CaMKII- and PKA-mediated effects were combined. In silico EADs were sensitive to computational ablation of either CaMKII-mediated slowing of ICaL inactivation, or PKA-mediated increase in peak ICaL.
CONCLUSIONS: Prior to HF, superimposing βAR stimulation upon CaMKII TG elicits EADs without DADs or severe Ca2+ dysregulation. This effect may rely upon interaction of PKA and CaMKII at ICaL. β agonist-induced EADs occurring prior to the development of HF constitute a novel arrhythmia mechanism accompanying CaMKII hyperactivity.
- Excitation-contraction coupling (ECC)
- Beta-adrenergic receptor agonists
- Cell signaling
- Ventricular arrhythmia
- © 2011 by American Heart Association, Inc.