Mitochondrial porins or voltage-dependent anion channels (VDAC) are beta-barrel pores located in the outer mitochondrial membrane. Mitochondrial porins allow the passage of ions and small molecule metabolites. At low or zero membrane potentials, the aqueous pore is in an open state, allowing the diffusion of small hydrophilic molecules with high conductance and anionic selectivity. At membrane potentials above 30-40mV the pore forms a closed state, but will still allow the passage of small ions with a low conductance and cationic selectivity. A voltage-sensitive domain controls gating. (Adapted from FBrf0167356.)