Holographic imaging of mitochondrial optical density in living cells reveals that the Mitochondrial Permeability Transition is a two-stage process
A sudden increase in permeability of the mitochondrial inner membrane, mitochondrial permeability transition (PT), is the central event responsible for cell death and tissue damage in conditions such as stroke and heart attack. PT is caused by the opening of the Cyclosporin A (CSA) dependent calcium-induced pore, the Permeability Transition Pore (PTP). The molecular details of PTP are incompletely understood. We utilized a combination of holographic and fluorescent microscopy to assess the contribution of the ATP synthase and Adenine Nucleotide Translocator (ANT) towards PTP. In cells lacking either ATP synthase or ANT, we observed CSA-sensitive membrane depolarization, but not high-conductance PTP. Further, we found that in wild-type cells calcium induced CSA-sensitive depolarization precedes opening of the PTP, which occurred until after nearly complete mitochondrial membrane depolarization. We propose that both ATP synthase and ANT are required for high conductance PTP but not depolarization, which presumably occurs through activation of the low conductance PT, which has a molecular nature that is different from both complexes.