Forms a channel through the mitochondrial outer membrane and also the plasma membrane. The channel at the outer mitochondrial membrane allows diffusion of small hydrophilic molecules; in the plasma membrane it is involved in cell volume regulation and apoptosis. It adopts an open conformation at low or zero membrane potential and a closed conformation at potentials above 30-40 mV. The open state has a weak anion selectivity whereas the closed state is cation-selective. In depolarized mitochondria, acts downstream of park to promote mitophagy or prevent apoptosis; polyubiquitination by park promotes mitophagy, while monoubiquitination by park decreases mitochondrial calcium influx which ultimately inhibits apoptosis