(Science: physiology) transmembrane proteins of excitable cells, that allow a flux of ions to pass only under defined circumstances. Channels may be either voltage gated, such as the sodium channel of neurons or ligand gated such as the acetylcholine receptor of cholinergic synapses. Channels tend to be relatively ion specific and allow fluxes of typically 1000 ions to pass in around 1ms, they are thus much faster at moving ions across a membrane than transport atpases.
noun, plural: ion channels
A single protein or protein complex that traverses the lipid bilayer of the cell membrane and form a channel to facilitate the movement of ions through the membrane according to their electrochemical gradient
Ion channels may be open or gated. The potassium leak channel is an example of open ion channel. Gated ion channels may be voltage-gated, ligand-gated, or mechanically-gated channels.
Ion channels are the common targets of pharmaceutical drugs, directly or indirectly, since they are capable of regulating the flow of ions to and from the cell. Many ions play in important physiological role in the normal metabolism of cells.