Menadione-induced apoptosis: roles of cytosolic Ca2+ elevations and the mitochondrial permeability transition pore

摘要

In normal pancreatic acinar cells, the oxidant menadione evokes repetitive cytosolic Ca2+ spikes, partial mitochondrial depolarisation, cytochrome c release and apoptosis. The physiological agonists acetylcholine and cholecystokinin also evoke cytosolic Ca2+ spikes but do not depolarise mitochondria and fail to induce apoptosis. Ca2+ spikes induced by low agonist concentrations are confined to the apical secretory pole of the cell by the buffering action of perigranular mitochondria. Menadione prevents mitochondrial Ca2+ uptake, which permits rapid spread of Ca2+ throughout the cell. Menadione-induced mitochondrial depolarisation is due to induction of the permeability transition pore. Blockade of the permeability transition pore with bongkrekic acid prevents activation of caspase 9 and 3. In contrast, the combination of antimycin A and acetylcholine does not cause apoptosis but elicits a global cytosolic Ca2+ rise and mitochondrial depolarisation without induction of the permeability transition pore. Increasing the cytosolic Ca2+ buffering power by BAPTA prevents cytosolic Ca2+ spiking, blocks the menadione-elicited mitochondrial depolarisation and blocks menadione-induced apoptosis. These results suggest a twin-track model in which both intracellular release of Ca2+ and induction of the permeability transition pore are required for initiation of apoptosis. [References: 54]