ELUCIDATING THE MOLECULAR MECHANISM OF THE PERMEABILITY TRANSITION PORE AND ITS ROLE IN REPERFUSION INJURY OF THE HEART

First, we present a summary of the evidence for our model of the molec ular mechanism of the permeability transition (MPT). Our proposal is t hat the MPT occurs as a result of the binding of mitochondrial cycloph ilin (CyP-D) to the adenine nucleotide translocase (ANT) in the inner mitochondrial membrane. This binding is enhanced by thiol modification of the ANT caused by oxidative stress or other thiol reagents. CyP-D binding enhances the ability of the ANT to undergo a conformational ch ange triggered by Ca2+. Binding of ADP or ATP to a matrix site of the ANT antagonises this effect of Ca2+; modification of other ANT thiol g roups inhibits ADP binding and sensitises the MPT to [Ca2+]. Increased membrane potential changes the ANT conformation to enhance ATP bindin g and hence inhibit the MPT. Our most recent data shows that a fusion protein of CyP-D and glutathione-S-transferase immobilised to Sepharos e specifically binds the ANT from Triton-solubilised inner mitochondri al membranes in a cyclosporin A (CsA) sensitive manner. Second we summ arise the evidence for the MPT being a major factor in the transition from reversible to irreversible injury during reperfusion of a heart f ollowing a period of ischaemia. We describe how in the perfused heart [H-3]deoxyglucose entrapment within mitochondria can be used to measur e the opening of MPT pore in situ. During ischaemia pore opening does not occur, but significant opening does occur during reperfusion, and recovery of the heart is dependent on subsequent pore closure. Pore op ening is inhibited by the presence in the perfusion medium of pyruvate and the anaesthetic propofol which both protect the heart from reperf usion injury. Third we discuss how the MPT may be involved in determin ing whether cell death occurs by necrosis (extensive pore opening and ATP depletion) or apoptosis (transient pore opening with maintenance o f ATP). (C) 1998 Elsevier Science B.V. All sights resented.