As inferred from rat heart mitochondria, hydrogen peroxide is released from mitochondria at a rate that is dependent on the membrane potential. Knockdown of Aquaporin-8 (AQP8) in human cells indicates that hydrogen peroxide is able to transit through the water channel of AQP8 located in the inner mitochodrial membrane (Marchissio et al. 2012). The resulting level of cytosolic hydrogen peroxide is hypothesized to signal the state of the mitochondria to regulatory molecules in the cytosol and nucleus (reviewed in Antico Arciuch et al. 2012).