Abstract 18794: Temporal Relationship Between Mitochondrial Membrane Potential (ΔΨm) Depolarization and Loss of Excitability in Globally Ischemic Rabbit Heart
Mitochondrial membrane potential (ΔΨm) depolarization has been implicated in the loss of excitability during ischemia, which could be relevant for resuscitation after cardiac arrest. The timing and degree of ΔΨm loss during no-flow ischemia in whole hearts is still poorly documented, in part due to the difficulty of estimating ΔΨm dynamics under this condition. We use a new approach based on the spatially periodic pattern present in the fluorescence emitted by potentiometric fluorophore TMRM when the dye accumulates in well-polarized mitochondria. This periodicity creates a distinct “mitochondrial” peak (MP) in the spatial Fourier spectrum corresponding to the sarcomere length (∼2 μm). Redistribution of TMRM upon ΔΨm depolarization diminishes the area under MP (MPA). We used Langendorff-perfused rabbit hearts mechanically uncoupled with blebbistatin (5.7μM) and stained with TMRM (450 nM). Confocal images were obtained from posterior left ventricular epicardium. Mitochondrial uncoupler FCCP (5 μM) and glycolytic inhibitior iodoacetate (IA, 15 mM) were used to validate MPA method. Eight hearts underwent minimum 1 hour global-ischemia; 4 hearts remained in sinus rhythm, 4 hearts were paced at 6.67 Hz to simulate ventricular fibrillation. FCCP reduced MPA to 32+/-6% of baseline; subsequent application of IA made MPA undetectable. During global ischemia ΔΨm loss started after a variable delay, was gradual and was not different between paced and non-paced hearts. MPA decreased to 50% of baseline at 44±17 (from 10 to 64) minutes and to 32% of baseline at 49±16 (from 27 to 70) minutes of ischemia. The minimum MPA value was 7±9% (range, 0-26%) of baseline and was observed at 65±9 minutes of ischemia (range, 51-72 minutes). Complete loss of excitability occurred earlier in paced than in non-paced hearts (33.2±3.1 vs. 45.0±7.2 min, p<0.05) but no clear relationship between ΔΨm dynamics and loss of excitability could be found.
Conclusions: In this model a significant ΔΨm loss, comparable with severe metabolic inhibition, occurs only after prolonged time of global ischemia, is not accelerated by rapid pacing and is not correlated with the loss of excitability. This suggests a limited the role of ΔΨm dynamics in the outcomes of resuscitation after sudden cardiac arrest.
- © 2012 by American Heart Association, Inc.