1 Introduction [1–3] [1–3] [4] [5,6] [1,3,7–10] [11–13] 2 The phenomenon of ischaemic preconditioning [14] [15–17] [14,18] [19] [15] [15,20–22] Section 6 [23–25] [25] 3 Causes of reperfusion injury 2+ [1,3,9,26] 3.1 Damage occurring in ischaemia (Reviewed in [1;3;26]) i + + i. + i 2+ + 2+ 2+ [27] [26,28–31] 2+ [1,3,26,32] [1,3] 3.2 Damage occurring during reperfusion [27] [26,28–30] [28] [26,31] [33–35] [36,37] [38] 2+ [1,3,10,26,39] 4 The mitochondrial permeability transition pore (MPTP) 4.1 Properties of the MPTP [3,40,41] [3,9,26] [42] [43] c [44,45] 4.2 The molecular identity of the MPTP [40,41,46] [46,47] [48] [49,50] [51,52] [53–55] [9,56] [57] [57] 160 [58] [58,59] [60] 2+ [61] [62] [63] [64] [3,40,41,65] [3,40,65] [66] [67] 5 The MPTP opening plays a central role in reperfusion injury 5.1 The MPTP opens during reperfusion but not ischaemia 3 [68] [69] [70,71] c [72] [68] [73] [74] [75] [75] [76–78] + + [3,79,80] [81,82] [1,9] 2+ 2+ [83] [27,84] [73] [1,3,9,65] [75,85] c Section 4.1 [5,6] [54,55] [46] 5.2 Inhibition of MPTP opening protects hearts from reperfusion injury [86] [68,87,88] [88,89] [90,91] [92] [93] [94] [80] [75,95] [75] [75,96] 5.3 Protection by preconditioning involves inhibition of MPTP opening [85] [69,97] [98] [85,99,100] [85,100] [99–101] Section 6 [101] [102] [101] 6 Signalling pathways linking preconditioning to inhibition of the MPTP [16,30,103–107] [30,103–107] 6.1 The role of protein kinase C [105] [103] [105] [108] [109–111] [112–114] [113–115] Fig. 1 [116] sections 7–10 [104] [27,117,118] [118–120] [100,101,118,121] [35,122] 6.2 The role of nitric oxide and cyclic GMP dependent protein kinase [106,123,124] ATP Section 9 ATP [123] ATP [125] Sections 7 [128] ATP Section 10.2 6.3 The role of pro-survival kinases [107,126] [107,127] [126,128–130] [106,107] [97] [131] [132] [53] 6.4 The role of AMP-activated protein kinase [133] ATP Section 10 [133] [134] [135] [136] [101] Taken together, all these data suggest that several signalling pathways may interact or act in parallel to induce IP, but the ultimate target of their action remains unclear. Since IP involves inhibition of the MPTP the signalling pathway must ultimately inhibit MPTP opening, but this could be achieved either by direct phosphorylation of a component of the MPTP or indirectly by influencing factors that enhance pore opening such as by reducing oxidative stress or calcium overload. 7 Mechanism of inhibition of the MPTP by IP 7.1 Is there evidence for regulation by phosphorylation? [115] [3,40] [137] [85,100] [97,113,114] Fig. 1 32 [138] [139] [140,141] [142,143] 32 32 [139,144] 32 [145] [142,146] Fig. 2 7.2 Effects of IP on ROS production and calcium loading during ischaemia and reperfusion as potential mediators of MPTP inhibition [83,147] [73] [27,84,148,149] [150–153] [85,100] [99–101] [100,101] [154] [155,156] 8 The role of mitochondrial potassium channels ATP [12,157] ATP ATP [146] ATP ATP [12,157] [158–160] ATP ATP [11,12,161–163] ATP ATP 8.1 + + + + + + [43,164] + [12] + [165,166] 8.2 + + [167–171] [172–174] + [168,175–179] + [180,181] + + + + [43,164,165,182] + 3 2 14 [165,182] [182] [44,49,170,183,184] [44,49,170,171] [44,49,170,171] [182] [185] [170] [171] Fig. 3 [170,171] Fig. 3 [171] + 8.3 ATP + [49,186,187] [188] [171] ATP [172] [189] [165,166] ATP Section 8.2 ATP ATP 2+ ATP ATP [176,177] [165] [165,168,190] ATP ATP ATP [167,168] ATP ATP [191–194] ATP ATP [12] [166,195] [195] [166] 125 [196] ATP ATP ATP [197] ATP ATP ATP ATP ATP Section 8.2 ATP [170,171] ATP [170,171] ATP ATP Section 9.1 8.4 + [182,198] + [182,198] 2+ [186] [199–201] + [202,203] [186] [188] + [186] [171] [180,204] [174] Ca Ca Ca Ca Ca 9 + 9.1 The use of pharmacological agents is hampered by lack of specificity ATP [11,12,161–163] [205,206] Ca ATP Ca Ca [13,174] Section 8.3 ATP Ca ATP [169,206–209] [210,211] [210] [212] ATP [206,209,213] [206,214] ATP [215–217] ATP ATP bona fide [31,218–221] [222] [223,224] ATP 9.2 ATP + 9.3 Measuring matrix volume in situ [206] ATP ATP [206] [97] ATP Section 8.2 [97] [225] + 9.4 Measuring flavoprotein oxidation + + + [226] Ca [227] [209,228] ATP + [169,229] [182] [228,230] + Section 9.1 [12] 10 + + 10.1 Enhanced mitochondrial ATP production [182,198] [161,231] [206] [206] ATP [11] + ATP [232,233] [232–235] ATP [206] 10.2 Mild uncoupling leads to less calcium overload and ROS production + [12,151,152,162,163,227,236] + [169,229] [228,230] [232,237,238] ATP [223,224] [218–221] [222] + [209–211,239] [169,206–209,240] Section 6.4 [218,241] [224] [242] [241] 10.3 Production of ROS as a signalling mechanism [240,243–248] [249,250] [12,100,240,245] ATP [182,251] [248] [11,163,247] [252] [182,251] + [253] [254] ATP [169,206–209,240] 11 Other proposed mechanism for inhibiting the permeability transition pore in preconditioning 11.1 The role of connexin 43 [255–258] [258–260] 2+ [258,259] Section 6 [261] [262,263] [261] [247] [255–257] [257] [256] Fig. 4 [247,261] [247] ATP [255,257] [257] [257] [256] 11.2 Transient MPTP opening [121] Section 6.1 [264] [68,75] [121] [264] 12 Conclusions and future directions Fig. 5 [85,100] Sections 6 7.1 [99–101] Section 7.1 [100,101] Section 7.2 [27,265] [26,28] Section 6 Section 9.1 [133,266] [101,135] [267] [90,91] [97,107,126] [268,269] [44] c [45] [72] c [70] [68,98] c [270,271] c c c [272] [273,274] [275] Note added in proof Since submission of this article it has been reported that the properties of the mitochondrial permeability transition pore in mitochondria devoid of all VDAC isoforms are the same as in mitochondria from wild-type mitochondria (C.P. Baines, R.A. Kaiser, T. Sheiko, W.J. Craigen, J.D. Molkentin, Voltage-dependent anion channels are dispensable for mitochondrial-dependent cell death, Nat Cell Biol. 9 (2007) 550–555). This confirms that VDAC is not an essential component of the MPTP.