Rat cardiac mitochondrial sub-populations show distinct features of oxidative phosphorylation during ischemia, reperfusion and ischemic preconditioning

Background: Inter-fibrillar (IFM) and sub-sarcolemmal (SSM) mitochondria are two distinct mitochondrial sub-populations and are expected to behave differently during pathological conditions. This study was undertaken to compare functional oxidative phosphorylation (OXPHOS) in IFM and SSM during ischemia, reperfusion and ischemic preconditioning. Methods: Langendorff perfused Wistar rat hearts were subjected to 35minutes ischemia, 60minutes reperfusion and ischemic preconditioning (IPC) procedure (3cycles of 2-minutes ischemia followed by 3-minutes reperfusion).Subsequently IFM and SSM were isolated, and mitochondrial electron transport chain (ETC) enzyme activities and respiration were measured immediately. Results: Functional enzyme activities of ETC in IFM and SSM showed prominent differences especially in the proximal part of ETC enzymes during ischemia and reperfusion. SSM favor FADH ₂ while IFM prefer NADH as the main reducing equivalent for electron transport during ischemia and reperfusion. IPC preserved ETC enzyme activities in both IFM and SSM rendering cardio protection. Similarly IPC preserve ADP stimulated respiration with glutamate and malate as substrate in both sub populations, but not in IFM, with succinate as substrate. Apparently, the preconditioning imparts enhanced protection more to SSM than IFM during ischemia and reperfusion and especially to the proximal part of the ETC. Conclusion: We propose that mitochondrial dysfunction, one of the major targets of myocardial ischemia reperfusion injury needs to be evaluated by the synergic effect of both IFM and SSM.