Mitochondrial permeability transition pore: an enigmatic gatekeeper

Mitochondrial permeability transition pore (MPTP) is a transient structure formed in the inner mitochondrial membrane (IMM) upon oxidative challenge of the organelle. The transition is a Ca 2+ -dependent increase of permeability of IMM leading to loss of transmembrane potential (∆ψm), mitochondrial swelling and, finally, rupture of outer mitochondrial membrane leading to release of factors causing apoptosis. Formation of this pore is an indication of the onset of necrotic cell death. In spite of several years of research, the molecular identity of this structure remains a mystery. The current review introduces MPTP, summarizes the research on various proteins that are thought to constitute the pore, enumerates factors that trigger pore formation, and the various experimental approaches that aid in understanding pore behavior.