Abstract 207: Mitochondrial Calcium Flux is Arrhythmogenic in Nonischemic Cardiomyopathy
Introduction: Mitochondria participate in Ca2+ homeostasis and Ca2+ oscillations are thought to be involved in arrhythmogenesis. Nevertheless, the role of mitochondria in arrhythmogenesis is unclear. We have reported spontaneous and induced arrhythmias in a mouse model of nonischemic cardiomyopathy, so we investigated the role of mitochondrial Ca2+ handling in arrhythmias in this model.
Methods: Nonischemic cardiomyopathy was induced in C57BL/6 mice by 6 weeks of hypertension evoked after unilateral nephrectomy, deoxycorticosterone acetate (DOCA) pellet implantation, and 1% salt water substitution. Sham operated mice were used as controls. ECG telemetry recording was used to monitor arrhythmias from DOCA mice and 7 sham mice at 18 weeks of age. Action potentials (APs) were recorded by perforated current-clamp in isolated mouse ventricular cells. Potassium and L-type Ca2+ currents were measured by voltage-clamp. Changes in cytoplasmic and mitochondrial Ca2+ were determined by fluorescent imaging using Fluo-4 and Rhod-2, respectively, in isolated ventricular cells.
Results: Seven DOCA mice and two sham mice had isoproterenol (0.5 mg/kg)-induced premature ventricular contractions (PVCs, p<0.05). Three DOCA mice and no sham mice had isoproterenol (2.5 mg/kg)-induced ventricular fibrillation. QTc was significantly prolonged from 41.9 ±1.4 in sham mice to 52.0 ± 2.1 ms in DOCA mice. At the cellular levels, myocytes had a prominent increase of APD90 from 66.6 ± 21.1 to 311.8 ± 44.9 ms, explained by augmented L-type Ca2+ current and decreased total K+ currents. Two of 12 sham mice ventricular cells and 8 from 12 DOCA mice ventricular cells had EADs (p<0.05). Three of 12 DOCA mice but none of the sham myocytes had PVCs with stimulated APs. Trigger activity could be abolished by 10 µM Ru360, a mitochondrial calcium uniporter specific antagonist. Ru360 had no effect on L-type Ca2+ current, total K+ currents, or APD90. Ru360 inhibited mitochondrial Ca2+ uptake in DOCA mice ventricular cells, implicating mitochondrial Ca2+ release in modulating the arrhythmic risk.
Conclusions: Mitochondrial Ca2+ handling appears to play an important role in triggered activity and may be important in the incidence of ventricular arrhythmias in nonischemic cardiomyopathy.
- © 2013 by American Heart Association, Inc.