S-15176 and its methylated derivative suppress the CsA-insensitive mitochondrial permeability transition and subsequent cytochrome c release induced by silver ion, and show weak protonophoric activity.

A recent report has described that S-15176 (N-[(3,5-di-tert-butyl-4-hydroxy-1-thiophenyl)]-3-propyl-N'-(2,3,4-trimethoxybenzyl) piperazine), an anti-ischemic agent, inhibits the mitochondrial permeability transition (PT) induced by not only Ca(2+) and inorganic phosphate, but also by tert-butylhydroperoxide or phenylarsine oxide [Morin et al. (Biochem Pharmacol 72:911-918, 2006)]. In the present study, we tested the effects of S-15176 on the PT induced by Ag(+), PT of which is not suppressed by cyclosporin A or oligomycin. S-15176 was effective in suppressing the PT and the subsequent cytochrome c release induced by Ag(+), and hence, it was concluded to be a more universal PT inhibitor than cyclosporin A or oligomycin. In addition to the PT-suppression activity, S-15176 also showed weak protonophoric activity. Thus, we further tested to investigate whether the hydroxyl group of S-15176 was involved in its PT-suppression or weak protonophoric activities. The methylated derivative of S-15176 also showed both PT suppression and weak protonophoric activities; hence, the hydroxyl group of S-15176 was concluded not to be involved in these activities.

Ca2+-induced permeability transition can be observed even in yeast mitochondria under optimized experimental conditions.

Yeast mitochondria have generally been believed not to undergo the permeability transition (PT) by the accumulation of Ca(2+) within the mitochondrial matrix, unlike mammalian mitochondria. However, the reason why the yeast PT is not induced by Ca(2+) has remained obscure. In this study, we examined in detail the effects of Ca(2+) on yeast mitochondria under various conditions. As a result, we discovered that the PT could be induced even in yeast mitochondria by externally added Ca(2+) under optimized experimental conditions. The 2 essential parameters for proper observation of the PT-inducing effects of Ca(2+) were the concentrations of the respiratory substrate and that of inorganic phosphate (Pi) in the incubation medium. The yeast mitochondrial PT induced by Ca(2+) was found to be insensitive to cyclosporin A and suppressed in the presence of a high concentration of Pi. Furthermore, when the PT was induced in yeast mitochondria by Ca(2+), the release of cytochrome c from mitochondria was also observed.

Distinct behaviors of adenylate kinase and cytochrome c observed following induction of mitochondrial permeability transition by Ca(2+) in the absence of respiratory substrate.

For induction of the mitochondrial permeability transition (PT) by Ca(2+), the addition of a respiratory substrate such as succinate is required. However, earlier studies indicated the possible induction of the mitochondrial PT by Ca(2+) in the absence of a respiratory substrate (Hunter, D.R., and Haworth, R.A. (1979) Arch. Biochem. Biophys. 195, 453-459). In the present study, we obtained clear evidence showing that the mitochondrial PT could be induced by Ca(2+) even in the absence of respiratory substrate. We next examined the protein release from mitochondria that accompanied the induction of PT in the absence of a respiratory substrate. Interestingly, distinct from the ordinary mitochondrial PT induced by Ca(2+) in the presence of a respiratory substrate, which is associated with the release of mitochondrial cytochome c and adenylate kinase, the mitochondrial PT occurring in the absence of a respiratory substrate was associated with release of mitochondrial adenylate kinase but not with that of mitochondrial cytochrome c. This experimental system should be quite useful for understanding the mechanisms of protein release from mitochondria.