Calpeptin, not calpain, directly inhibits an ion channel of the inner mitochondrial membrane

The permeability transition pore (PTP) of inner mitochondrial membranes is a large conductance pathway for ions up to 1500 Da which opening is responsible for ion equilibration and loss of membrane potential in apoptosis and thus in several neurodegenerative diseases. The PTP can be regulated by the Ca2+-activated mitochondrial K channel (BK). Calpains are Ca2+-activated cystein proteases; calpeptin is an inhibitor of calpains. We wondered...