Commitment to apoptosis by GD3 ganglioside depends on opening of the mitochondrial permeability transition pore

We have studied the effects of GD3 ganglioside on mitochondrial function in isolated mitochondria and intact cells, In isolated mitochondria, GD3 gang lioside induces complex changes of respiration that depend on the substrate being oxidized. However, these effects are secondary to opening of the cyc losporin A-sensitive permeability transition pore and to the ensuing swelli ng and cytochrome c depletion rather than to an interaction with the respir atory chain complexes. By using a novel in situ assay based on the fluoresc ence changes of mitochondrially entrapped calcein (Petronilli, V., Miotto, G., Canton, M., Colonna, R., Bernardi, P., and Di Lisa, F. (1999) Biophys, J. 76, 725-734), we unequivocally show that GD3 ganglioside also induces th e mitochondrial permeability transition in intact cells and that this event precedes apoptosis, The mitochondrial effects of GD3 ganglioside are selec tive, in that they cannot be mimicked by either GD1a or GM3 gangliosides, a nd they are fully sensitive to cyclosporin A, which inhibits both the mitoc hondrial permeability transition in situ and the onset of apoptosis induced by GD3 ganglioside, These results provide compelling evidence that opening of the permeability transition pore is causally related to apoptosis.