Bcl-2 prevents apoptotic mitochondrial dysfunction by regulating proton flux

We and others have recently shown that lolls of the mitochondrial membrane potential (Delta psi) precedes apoptosis and chemical-hypoxia-induced necrosis and is prevented by Bcl-2. In this report, we examine the biochemical mechanism used by Bcl-2 to prevent Delta psi loss, as determined with mitochondria isolated from a cell line overexpressing human Bcl-2 or from livers of Bcl-2 transgenic mice, Although Bcl-2 had no effect on the respiration rate of isolated mitochondria, it prevented both Delta psi loss and the permeability transition (PT) induced by various reagents, including Ca2+, H2O2, and tert-butyl hydroperoxide, Even under conditions that did not allow PT, Bcl-2 maintained Delta psi, suggesting that the functional target of Bcl-2 is regulation of Delta psi but not PT. Bcl-2 also maintained Delta psi in the presence of the protonophore SF6847, which induces proton influx, suggesting that Bcl-2 regulates ion transport to maintain Delta psi. Although treatment with SF6847 in the absence of Ca2+ caused massive H+ influx in control mitochondria, the presence of Bcl-2 induced H+ efflux after transient H+ influx, In this case, Bcl-2 did not enhance K+ efflux, Furthermore, Bcl-2 enhanced H+ efflux but not K+ flux after treatment of mitochondria with Ca2+ or tert-butyl hydroperoxide, These results suggest that Bcl-2 maintains Delta psi by enhancing H+ efflux in the presence laf Delta psi-loss-inducing stimuli.