Abstract 2364: The Mitochondrial Permeability Transition Pore Opens During Ventricular Fibrillation in a Rat Model of Closed Chest Resuscitation
Objective: Myocardial injury during cardiac arrest and resuscitation is associated with mitochondria Ca2+ overload, cytochrome c release, and impaired bioenergetics. An important mechanism of mitochondrial injury is opening of the mitochondrial permeability transition pore (mPTP). A technique using tritium-labeled 2-deoxyglucose ([3H]DOG), previously developed for measuring mPTP opening in isolated cells or heart tissue, was adapted for in vivo measurement in an intact rat model of ventricular fibrillation (VF) and resuscitation.
Methods: VF was electrically induced and left untreated for 10 mins. Closed-chest resuscitation was then provided for 8 mins and VF terminated by electrical shocks enabling return of spontaneous circulation and post-resuscitation (PR) monitoring for up to 240 mins. Hearts from 25 rats were randomized to be removed immediately before inducing VF (control group; n=5), at the end of untreated VF (n=5), at the end of chest compression (n=6), at PR 60-mins (n=5), or at PR 240-mins (n=5). To measure mPTP opening, rats received a 50 μCi [3H]DOG bolus prior to randomization. To correct for variation in intact mitochondrial yield, mitochondrial [3H] was normalized by citrate synthase activity. To correct for variation in total heart [3H]DOG uptake, total heart [3H] was normalized to the sample wet-weight. mPTP opening was expressed as a ratio: 105 × Mitochondrial [3H] dpm per IU citrate synthase/Total heart [3H] dpm per g wet-weight
Results: Resuscitated rats demonstrated marked PR myocardial dysfunction with an average survival time of 202±57 mins and only 2/5 rats surviving 240 mins. The mPTP opening ratio in control hearts was 0.30±0.03 and significantly lower than the mPTP ratio of hearts removed during VF (0.50±0.06, p<0.005), at the end of closed-chest resuscitation (0.56±0.11, p<0.001), at PR 60-mins (0.55±0.14, p<0.001), and at PR 240-mins (0.50±0.05, p<0.005).
Conclusions: In this rat model of VF and resuscitation the mPTP opened during untreated VF without evidence of further opening during or after resuscitation. This differs from in situ models of ischemia and reperfusion where mPTP opening is reported only after reperfusion. Further work is required to understand the mechanisms contributing to mPTP opening during VF,