ion channel activity Enables the facilitated diffusion of an ion (by an energy-independent process) by passage through a transmembrane aqueous pore or channel without evidence for a carrier-mediated mechanism. May be either selective (it enables passage of a specific ion only) or non-selective (it enables passage of two or more ions of same charge but different size). GO:0005216 go.owl molecular_function obi.owl ion transmembrane transporter activity substrate-specific channel activity