Ligandgated

Ligand-gated, typically referring to ligand-gated ion channels, describes receptors or channels that activate directly upon binding a chemical ligand. The ligand is usually a neurotransmitter, hormone, drug, or other signaling molecule. Binding induces a conformational change that opens or closes an ion pore, allowing selective ions to pass and producing rapid changes in membrane potential and cellular signaling.

Ligand-gated ion channels mediate fast synaptic transmission and are found throughout the nervous system and other tissues. They are generally oligomeric, with subunits arranged to form a pore that is gated by extracellular ligand binding. Major families include pentameric Cys-loop receptors such as nicotinic acetylcholine, GABA_A, GABA_C, and glycine receptors, and tetrameric glutamate receptors such as NMDA, AMPA, and kainate receptors. Additional examples include P2X receptors gated by extracellular ATP and cyclic nucleotide-gated channels gated by cyclic nucleotides.

Ligand-gated channels are contrasted with voltage-gated channels, which respond to changes in membrane potential, and with metabotropic receptors, which signal through intracellular second messenger cascades rather than direct ion flow.

Pharmacologically, ligand-gated channels are important drug targets. Subunit composition, binding site accessibility, and channel kinetics influence ligand affinity and selectivity. Clinically relevant modulators include benzodiazepines, barbiturates, anesthetics, nicotine, and various anticonvulsants and toxins. Dysfunction or dysregulation of ligand-gated channels is associated with epilepsy, chronic pain, anxiety disorders, and other neurological conditions.