Silver Ion Induces a Cyclosporine A-Insensitive Permeability Transition in Rat Liver Mitochondria and Release of Apoptogenic Cytochrome c

Various reagents are known to open the mitochondrial permeability pore (PTP) and induce a permeability transition (PT), releasing apoptogenic proteins from the intermembrane space and triggering apoptosis. In this study, we examined the effect of Ag(+), a known cytotoxic sulfhydryl-reactive heavy metal, on isolated rat liver mitochondria. The following results were obtained: (1) Upon addition, Ag(+) instantly induced mitochondrial swelling and acceleration of respiration. (2) Cyclosporine A, a specific inhibitor of classical PT, was ineffective against the effect of Ag(+), indicating that silver ions induced non-classic PT. (3) Sulfhydryl reagents such as reduced glutathione completely inhibited the effects of Ag(+) on the mitochondria. (4) Experimental results using polyethylene glycol indicated that Ag(+) induced opening of a pore in the inner mitochondrial membrane, which could be PTP of another open state or a distinct pore. (5) Electron microscopic analysis of mitochondria treated with Ag(+) showed a novel mitochondrial configuration that was apparently different from that of normal mitochondria or Ca(2+)-treated mitochondria. (6) Ag(+) also induced the release of apoptogenic cytochrome c in a CsA-insensitive but GSH-sensitive manner. These results suggest that Ag(+) promotes a nonclassical permeability increase in the mitochondrial inner membrane that is clearly distinguishable from the classical PT and releases apoptogenic cytochrome c in a classical PT-independent manner.