Nicotinic Acetylcholine Receptors in Health and Disease
Subunits
Ronald J. Lukas, PhD, Director
Subunits are the building blocks of nicotinic acetylcholine receptors (nAChR). Nicotinic acetylcholine receptors are neurotransmitter-gated ion channels. Opening of the channel is triggered by the presence of nicotine or acetylcholine and allows positively charged ions to flow down their concentration gradients across the plasma membrane.
Nicotinic acetylcholine receptors exist as diverse subtypes expressed in different tissues or cells. For example, nicotinic receptors in adult mammalian muscle are different from two types of receptors in autonomic neurons and from the predominant types of receptors in the brain. Each distinct nicotinic receptor subtype is composed of different combinations of genetically distinct subunits. The subunits themselves are made up of transmembrane proteins, and it is thought that a complete nicotinic receptor is composed of five subunits. Subunits assemble in a fashion similar to the staves or planks of a wooden barrel to create a central empty space—the ion channel.
Evolutionary and protein sequence relationships between nicotinic receptor subunits from different species are known (see Lukas, 1998, and Lukas et al., 1999, for details). The most closely related subunits include alpha4 and alpha2, alpha6 and alpha3, and beta2 and beta3. The most ancient subunits (e.g., alpha7) also form the simplest types of receptors constructed from a single type of subunit.
Genetic variations of the nicotinic receptor subunits exist across individuals and are known, in some cases, to contribute to or to cause neurological diseases. It is also possible that they could influence individual behavior, such as susceptibility to use of tobacco products.
For more information about nicotine receptors, visit The Ligand Gated Ion Channel Database. [This website link is provided for your convenience only. Barrow Neurological Institute neither endorses nor is responsible for the content in any way.]
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