A heart mitochondrial Ca2+-dependent pore of possible relevance to re-perfusion-induced injury. Evidence that ADP facilitates pore interconversion between the closed and open states

Abstract

The permeability properties of a putative Ca2(+)-activated pore in heart mitochondria, of possible relevance to re-perfusion-induced injury, have been investigated by a pulsed-flow solute-entrapment technique. The relative permeabilities of [14C]mannitol, [14C]sucrose and arsenazo III are consistent with permeation via a pore of about 2.3 nm diameter. Ca2+ removal with EGTA induced pore closure, and the mitochondria became 'resealed'. The permeability of the unresealed mitochondria during resealing was markedly stimulated by 200 microM-ADP, and the relative permeabilities to solutes of different size were stimulated equally, indicating an increase in open-pore number, rather than an increase in pore dimensions. This is paradoxical, since ADP also stimulated the rate of resealing. The rate of EGTA-induced resealing was also stimulated by the Ca2+ ionophore A23187, which indicates that the rate of removal of matrix free Ca2+ is limiting for pore closure. An explanation for the paradox is suggested in which ADP facilitates pore interconversion between the closed and open states in permeabilized mitochondria, and pore closure in Ca2(+)-free mitochondria occurs much faster than previously thought.

The mitochondrial permeability transition pore and its role in cell death

“…Subsequently a rapid-pulsedflow technique was used to measure ["%C]solute fluxes directly. There was an inverse relation between permeability and molecular size which, when analysed according to the Renkin equation, indicated a pore radius of 1.0-1.3 nm [30,31]. Since the hydrodynamic radius of poly(ethylene glycol) 1500 is about 1.2 nm [32], the two sets of measurement are in close agreement.…”

“…If the basic function of mitochondrial Ca# + is to control the tricarboxylic acid cycle and mitochondrial ATP production (section 1.1), mitochondrial Ca# + itself is unlikely to be regulated by a mechanism (PT pore) that allows tricarboxylic-acid-cycle intermediates to be lost to the cytosol and ATP to be hydrolysed. On these and other grounds we have argued [30,31] that PT pore opening is a critical event leading to Ca# + -induced cell death, rather than an ongoing Ca# + control mechanism of viable cells.…”

“…In fact, transient opening appears to be its normal mode of behaviour. This becomes evident as follows : When pore-activated mitochondria are treated with EGTA to chelate Ca# + , pores are closed immediately ( 50 ms [31]), entrapping EGTA in the matrix. If this is done with Ca# + \N-hydroxyethylethylenediaminetriacetic acid (' HEDTA ') buffers and uniporter inhibitors, then the buffer is entrapped ; but, with finite free Ca# + in the mitochondrial matrix, pores can reopen, admitting sucrose.…”

Role of the c subunit of the FOATP synthase in mitochondrial permeability transition

“…9,13 During the last couple of decades, two models have been put forward to mechanistically link MPT with the observation that the PTPC can assume two distinct states of conductance. 16 On one hand, it has been proposed that one of the main PTPC components, i.e., voltagedependent anion channel (VDAC), would normally exist in an "open" state and would promote MPT upon "closure." 17,18 On the other hand, a low-conductance conformation of the PTPC has been suggested to allow for the physiological exchange of metabolites between the mitochondrial matrix and the cytosol.…”

The presence of two classes of high‐affinity cyclosporin A binding sites in mitochondria

“…There is evidence for a continual interconversion of pores between the closed and open states in permeabilized mitochondria [7, 11,131, and (C) Thc rate constants (kisom) for cis-trans-isomerization were obtained from plots of the type shown in B; they were corrected for thc rate of isomerization in the absence of mitochondria and refer to isomerase activity since any such interconversion would entail reversible conformational change in the pore protein, it was relevant to examine isomerase involvement. In Fig.…”