tailieunhanh - Nicotinic acetylcholine receptors

Nicotinic acetylcholine receptors, or nAChRs, are cholinergic receptors that form ligand-gated ion channels in the plasma membranes of certain neurons and on the postsynaptic side of the neuromuscular junction . Being ionotropic receptors, nAChRs are directly linked to an ion channel and do not make use of a second messenger as metabotropic receptors do. | Nicotinic acetylcholine receptors Nicotinic acetylcholine receptors or nAChRs are cholinergic receptors that form ligand-gated ion channels in the plasma membranes of certain neurons and on the postsynaptic side of the neuromuscular junction . Being ionotropic receptors nAChRs are directly linked to an ion channel and do not make use of a second messenger as metabotropic receptors do. Like the other type of acetylcholine receptors muscarinic acetylcholine receptors mAChRs the nAChR is triggered by the binding of the neurotransmitter acetylcholine ACh . However whereas muscarinic receptors are also activated by muscarine nicotinic receptors are also opened by nicotine. Hence the name nicotinic . Nicotinic acetylcholine receptors are present in many tissues in the body and are the best-studied of the ionotropic receptors. The neuronal receptors are found in the central nervous system and the peripheral nervous system. The neuromuscular receptors are found in the neuromuscular junctions of somatic muscles stimulation of these receptors causes muscular contraction. Structure Nicotinic receptors with a molecular mass of 290 kDa are made up of five subunits arranged symmetrically around a central pore. They possess similarities with GABAA receptors glycine receptors and the type 3 serotonin receptors which are all ionotropic receptors or the signature Cys-loop proteins. Nicotinic receptors are broadly classified into two subtypes based on their primary sites of expression muscle-type nicotinic receptors and neuronal-type nicotinic receptors. In the muscle-type receptors found at the neuromuscular junction receptors are either the embryonic form composed of al p1 Ỗ and Y subunits in a 2 1 1 1 ratio or the adult form composed of al pi Ỗ and subunits in a 2 1 1 1 ratio. The neuronal subtypes are various homomeric or heteromeric combinations of twelve different nicotinic receptor subunits a2 through a10 and p2 through p4. Examples of the neuronal subtypes include a4p2 a4p2 .