Mitochondrial permeability transition (MPT) is critical in cardiomyocyte death during reperfusion but it is not the only mechanism responsible for cell injury. The objectives of the study is to investigate the role of the duration of
myocardial ischemia on mitochondrial integrity and cardiomyocyte death. Mitochondrial membrane potential (ΔΨm, JC-1) and MPT (
calcein) were studied in cardiomyocytes from wild-type and
cyclophilin D (CyD) KO mice refractory to MPT, submitted to simulated
ischemia and 10 min reperfusion. Reperfusion after 15 min simulated
ischemia induced a rapid recovery of ΔΨm, extreme cell shortening (
contracture) and mitochondrial
calcein release, and CyD ablation did not affect these changes or cell death. However, when reperfusion was performed after 25 min simulated
ischemia, CyD ablation improved ΔΨm recovery and reduced
calcein release and cell death (57.8 ± 4.9% vs. 77.3 ± 4.8%, P < 0.01). In a Langendorff system, CyD ablation increased
infarct size after 30 min of
ischemia (61.3 ± 6.4% vs. 45.3 ± 4.0%, P = 0.02) but reduced it when
ischemia was prolonged to 60 min (52.8 ± 8.1% vs. 87.6 ± 3.7%, P < 0.01). NMR spectroscopy in rat hearts showed a rapid recovery of
phosphocreatine after 30 min
ischemia followed by a marked decay associated with
contracture and LDH release, that were preventable with contractile blockade but not with
cyclosporine A. In contrast, after 50 min
ischemia,
phosphocreatine recovery was impaired even with contractile blockade (65.2 ± 4% at 2 min), and
cyclosporine A reduced
contracture, LDH release and
infarct size (52.1 ± 4.2% vs. 82.8 ± 3.6%, P < 0.01). In conclusion, the duration of
ischemia critically determines the importance of MPT on
reperfusion injury. Mechanisms other than MPT may play an important role in cell death after less severe
ischemia.