The Ca2+ threshold for the mitochondrial permeability transition and the content of proteins related to Bcl-2 in rat liver and Zajdela hepatoma mitochondria

Zajdela hepatoma mitochondria were able to accumulate two to five times mor e Ca2+ than rat liver mitochondria before the permeability transition was i nduced. Pulses of Ca2+ were given in series to determine the Ca2+ threshold by recording changes in [Ca2+] and membrane potential, the permeability tr ansition causing the release of accumulated Ca2+ and collapse of the membra ne potential. Hepatoma mitochondria had lower Ca2+ efflux rates, higher net Ca2+ uptake rates and lower phosphorylation rates than liver mitochondria. Since the differences in regard to induction of the permeability transitio n might be due to higher expression of the Bcl-2 protein in hepatoma cells than in hepatocytes, the transcription of Bcl-2 and the proteins reacting w ith a Bcl-2 polyclonal antiserum were estimated by Northern and Western blo tting, respectively. Hepatoma cells had two Bcl-2 specific mRNA bands of 7 and 2.4 kb, and substantial amounts of the Bcl-2 protein, whereas in liver cells and mitochondria these were not detected. Both cell lines had a react ive band at 19-20 kDa, and hepatocytes a small band at 31-32 kDa. Bcl-2 ant ibodies stimulated the permeability transition potently in hepatoma mitocho ndria.