Ca2+-induced reactive oxygen species production promotes cytochrome c release from rat liver mitochondria via mitochondrial permeability transition (MPT)-dependent and MPT-independent mechanisms: role of cardiolipin.

Release of cytochrome c from mitochondria is considered a critical, early event in the induction of an apoptosis cascade that ultimately leads to programmed cell death. Mitochondrial Ca(2+) loading is a trigger for the release of cytochrome c, although the molecular mechanism underlying this effect is not fully clarified. This study tested the hypothesis that distinct Ca(2+) thresholds may induce cytochrome c release from rat liver mitochondria by membrane permeability transition (MPT)-dependent and independent mechanisms. The involvement of reactive oxygen species (ROS) and cardiolipin in the Ca(2+)-induced cytochrome c release was also investigated. Cytochrome c was quantitated by a new, very sensitive, and rapid reverse-phase high performance liquid chromatography method with a detection limit of 0.1 pmol/sample. We found that a low extramitochondrial Ca(2+) level (2 microM) promoted the release of approximately 13% of the total alamethicin releasable pool of cytochrome c from mitochondria. This release was not depending of MPT; it was mediated by Ca(2+)-induced ROS production and cardiolipin peroxidation and appears to involve the voltage-dependent anion channel. High extramitochondrial Ca(2+) level (20 microM) promoted approximately 45% of the total releasable pool of cytochrome c. This process was MPT-dependent and was also mediated by ROS and cardiolipin. It is suggested that distinct Ca(2+) levels may determine the mode and the amount of cytochrome c release from rat liver mitochondria. The data may help to clarify the molecular mechanism underlying the Ca(2+)-induced release of cytochrome c from rat liver mitochondria and the role played by ROS and cardiolipin in this process.