Different mechanisms of mitochondrial proton leak in ischaemia/reperfusion injury and preconditioning: implications for pathology and cardioprotection

Abstract

The mechanisms of mitochondrial proton (H+) leak under various pathophysiological conditions are poorly understood. In the present study it was hypothesized that different mechanisms underlie H+ leak in cardiac IR (ischaemia/reperfusion) injury and IPC (ischaemic preconditioning). Potential H(+) leak mechanisms examined were UCPs (uncoupling proteins), allosteric activation of the ANT (adenine nucleotide translocase) by AMP, or the PT (permeability transition) pore. Mitochondria isolated from perfused rat hearts that were subjected to IPC exhibited a greater H+ leak than did controls (202+/-27%, P<0.005), and this increased leakage was completely abolished by the UCP inhibitor, GDP, or the ANT inhibitor, CAT (carboxyattractyloside). Mitochondria from hearts subjected to IR injury exhibited a much greater amount of H+ leak than did controls (411+/-28%, P<0.001). The increased leakage after IR was weakly inhibited by GDP, but was inhibited, >50%, by carboxyattractyloside. In addition, it was inhibited by cardioprotective treatment strategies including pre-IR perfusion with the PT pore inhibitors cyclosporin A or sanglifehrin A, the adenylate kinase inhibitor, AP5A (diadenosine pentaphosphate), or IPC. Together these data suggest that the small increase in H+ leak in IPC is mediated by UCPs, while the large increase in H+ leak in IR is mediated by the ANT. Furthermore, under all conditions studied, in situ myocardial O2 efficiency was correlated with isolated mitochondrial H+ leak (r2=0.71). In conclusion, these data suggest that the modulation of H+ leak may have important implications for the outcome of IR injury.

Cardioprotection and mitochondrial S-nitrosation: Effects of S-nitroso-2-mercaptopropionyl glycine (SNO-MPG) in cardiac ischemia–reperfusion injury

“…Inhibition of these events is proposed to underlie the cardioprotective effects of mitochondrial K + ATP channel opening [7], uncoupling protein activation [10,11], Na + /H + exchange inhibitors [72], Na + /Ca 2+ exchange inhibitors [73], mitochondrial Ca 2+ uniporter inhibitors [74], and mitochondrially targeted ROS scavengers [75,76]. In support of such a mechanism, SNO-MPG delivered prior to ischemia significantly improved mitochondrial Ca 2+ handling, inhibited ROS generation, and inhibited complex I, at the end of ischemia (Figures 5E & 7).…”

“…Isolated rat hearts were retrograde perfused in Langendorff mode under constant flow, essentially as described [10]. Hearts were subjected to one of the following protocols: (i) IR consisting of 25 min.…”

“…Mitochondria were isolated from hearts as previously described [10]. Protein was determined by the Lowry method [37] against a standard curve constructed using BSA.…”

“…Despite numerous studies the precise mechanisms of IPC are still under debate, but the preservation of mitochondrial function is believed to be an important end-point in IPC signaling. Several protective IPC mechanisms are intrinsic to mitochondria, including opening of K + ATP channels [6][7][8], activation of uncoupling proteins (UCPs) [9][10][11], modulation of ROS generation [12], or regulation of signaling pathways that impact on the PT pore [13,14]. The complex interplay between these mitochondrial IPC end-points and the upstream cytosolic signals that control them is an area of acute interest.…”

Adenine nucleotide translocase family: four isoforms for apoptosis modulation in cancer

“…ANT isoforms family C Brenner et al uncoupling function has undoubtedly important implications for pathology and cardioprotection (Nadtochiy et al, 2006), but remains to be investigated in cancer. Interestingly, the functions of ANT could depend on the dynamics of the mitochondrial networks, that is the balance between the mitochondrial fusion/fission events.…”