Inorganic polyphosphate (polyP) is a polymer that consists of a series of orthophosphates connected by high-energy phosphoanhydride bonds, like those found in ATP. In mammalian mitochondria, polyP has been linked to the activation of the mitochondrial permeability transition pore (mPTP). However, the details of this process are not completely understood. The activation of mPTP by polyP may involve the regulation of bioenergetics, Ca