GRADUAL CHANGES IN PERMEABILITY OF INNER MITOCHONDRIAL-MEMBRANE PRECEDE THE MITOCHONDRIAL PERMEABILITY TRANSITION

Some compounds are known to induce solute-nonselective permeability of the inner mitochondrial membrane (IMM) in Ca-2+-loaded mitochondria, Existing data suggest; that this process, following the opening of a m itochondrial permeability transition pope, is preceded by different so lute-selective permeable states of IMM. At pH 7, for instance, the K-0 .5 for Ca2+-induced pore opening is 16 mu M, a value 80-fold above a t herapeutically relevant shift of intracellular Ca2+ during ischemia in vivo. The present work shows that in the absence of Ca2+, phenylarsin e oxide and tetraalkyl thiuram disulfides (TDs) are able to induce a c omplex sequence off IMM permeability changes. At first, these agents a ctivated san electrogenic K+ influx into the mitochondria. This K+-spe cific pathway had K-0.5 = 35 mM for K+ and was inhibited by bromsulfal ein with K-i = 2.5 mu M. The inhibitors of mitochondrial K-ATP channel , ATP and glibenclamide, did not inhibit K+ transport via this pathway . Moreover, 50 mu M glibenclamide induced by itself K+ influx into the mitochondria. After the increase in K+ permeability of IMM, mitochond ria become increasingly permeable to protons. Mechanisms of H+ leak an d nonselective permeability increase could also be different depending on the type of mitochondrial permeability transition (MPT) inducer. T hus, permeabilization of mitochondria induced by phenylarsine oxide wa s fully prevented by ADP and/or cyclosporin A, whereas TD-induced memb rane alterations were insensitive toward these inhibitors. It is sugge sted that MPT in vivo leading to irreversible apoptosis is irrelevant in reversible ischemia/reperfusion injury. (C) 1998 Academic Press.