Nicotinic acetylcholine receptors

Nicotinic acetylcholine receptors (nAChRs) are protein structures that are found in the synaptic cleft of the nervous system. They are named for their ability to bind to the neurotransmitter acetylcholine (ACh) and the plant alkaloid nicotine. nAChRs are involved in a wide range of physiological processes, including muscle contraction, heart rate regulation, and learning and memory functions.

Structure

nAChRs are ionotropic receptors, meaning they are ligand-gated ion channels. They are composed of five subunits arranged symmetrically around a central pore. Each subunit is made up of four transmembrane domains (M1-M4). The M2 domain lines the ion channel pore. The subunits that make up the receptor can vary, leading to a diversity of nAChR subtypes with different functional properties.

Function

When acetylcholine or nicotine binds to the nAChR, it causes a conformational change in the receptor, opening the ion channel. This allows the flow of sodium and potassium ions across the cell membrane, leading to a depolarization of the cell and the initiation of an action potential. This is the basic mechanism by which nAChRs mediate fast synaptic transmission in the nervous system.

Clinical significance

nAChRs are the target of various drugs and toxins. For example, nicotine from tobacco smoke acts as an agonist at nAChRs, leading to the addictive properties of smoking. Certain snake venoms contain toxins that block nAChRs, causing paralysis. In addition, mutations in nAChR subunits have been linked to a number of neurological disorders, including myasthenia gravis and epilepsy.

See also

• Muscarinic acetylcholine receptor
• G protein-coupled receptor
• Neurotransmitter receptor