Ligand-gated Ion Channels

Ligand-gated ion channels are a large group of intrinsic transmembrane proteins that allow passage of ions upon activation by a specific chemical. Most endogenous ligands bind to a site distinct from the ion conduction pore and binding directly causes opening or closing of the channel. Ligands can bind extracellularly, e.g. glutamate, ACh and GABA, or intracellularly, e.g. Ca²⁺ on Ca²⁺-activated potassium channels. It is important to note that the ligand itself is not transported across the membrane. Ligand binding causes a drastic change in the permeability of the channel to a specific ion or ions; effectively no ions can pass through the channel when it is inactive but up to 10⁷ ions per second can be allowed through upon ligand binding.