Involvement of mitochondrial swelling in cytochrome c release from mitochondria treated with calcium and Alloxan

An early event in the induction of apoptosis is cytochrome c (Cyt c) release from mitochondria. We investigated the involvement of mitochonrial permeability transition (MPT) and mitochondrial swelling in Cyt c release from mitochondria treated with alloxan and/or calcium (Ca2+). When mitochondria were treated with a high concentration of Ca2+. alone or Ca2+. with alloxan (alloxan-Ca2+), the MPT was accompanied by mitochondrial swelling and the release of Cyt c. Cyclosporin A prevented the induction of MPT but only slightly decreased the release of Cyt c. High molecular weight polyethylene glycol almost completely inhibited MPT-dependent osmotic mitochondrial swelling and Cyt c release. However, MPT-independent mitochondrial swelling and Cyt c release induced by exogenous K+. were inhibited by the high molecular weight polyethylene glycol. Ruthenium red strongly decreased the amount of Cyt c released. These results suggest that mitochondrial swelling but not MPT is necessary for Cyt c release induced by Ca2+ alone or alloxan and Ca2+.