Abstract 332: Mitochondrial Inner-Membrane Potential Instability Promotes Sarcolemmal Electrical Instability after Ischemia-Reperfusion in Monolayers of Cardiac Myocytes
Mitochondrial uncoupling due to oxidative stress can, through opening of sarcolemmal KATP channels, alter cellular electrical excitability, and it has been proposed that mitochondrial function is a major factor in arrhythmogenesis during ischemia-reperfusion. Here, we examine the effects of ischemia-reperfusion on mitochondrial inner membrane potential (ΔΨm) and corresponding changes in electrical excitability and wave propagation in monolayer cultures of neonatal rat ventricular myocytes. Changes in ΔΨm were observed using TMRM and changes in the sarcolemmal voltage were recorded with a 464-element photodiode array using di-4-ANEPPS. Ischemia was induced by covering the center part of the monolayer (D = 22 mm) with a coverslip (D = 15 mm). Cell contractions ceased after approximately 6 min of ischemia; however, electrical activity continued for 11.3 ± 4.2 min (N = 5). Amplitude and conduction velocity of the action potentials in the ischemic region decreased over the same time period. ΔΨm was lost in two phases: a reversible phase of partial depolarization, after 11.2 ± 1.3 min of ischemia, and a nonreversible phase, which happened after 30 ± 6 min of ischemia, during which the whole mitochondrial network of the myocyte became depolarized and the cells underwent contracture (N = 4). Reperfusion after the long ischemia resulted in only partial recovery and the observance of oscillations of ΔΨm in the mitochondrial network or rapid flickering of individual mitochondrial clusters and was associated with heterogeneous electrical recovery, and formation of wavelets and reentry (4/5 monolayers). In contrast, mitochondria fully recovered and reentry was rare (1/5 monolayers) for reperfusion after the short ischemia (10-12 min). 4’-chlorodiazepam, an inhibitor of inner membrane anion channels, stabilized mitochondrial function after the long ischemia, and prevented wavelets (5/5 monolayers) and reentry (4/5 monolayers). In conclusion, incomplete or unstable recovery of mitochondrial function after ischemia correlates with reentrant arrhythmias in monolayers of cardiac myocytes. Our findings suggest that stabilization of mitochondrial network dynamics is an important strategy for preventing ischemia/reperfusion-related arrhythmias.
- © 2013 by American Heart Association, Inc.