Forms a channel through the mitochondrial outer membrane that allows diffusion of small hydrophilic molecules. The channel adopts an open conformation at low or zero membrane potential and a closed conformation at potentials above 30-40 mV. The open state has a weak anion selectivity whereas the closed state is cation-selective (By similarity). Interacts with hexokinases. Expressed in skeletal muscle and oocytes. Consists mainly of a membrane-spanning beta-barrel formed by 19 beta-strands. Belongs to the eukaryotic mitochondrial porin family.