Everything about Cholinergic Receptor totally explained
An
acetylcholine receptor (abbreviated
AChR) is an
integral membrane protein that responds to the binding of the
neurotransmitter acetylcholine.
Classification
Like other
transmembrane receptors, acetylcholine receptors are classified according to their "pharmacology", or according to their relative affinities and sensitivities to different molecules. Although all acetylcholine receptors, by definition, respond to acetylcholine, they respond to other molecules as well.
Receptor types
Molecular biology has shown that the nicotinic and muscarinic receptors belong to distinct protein
superfamilies.
nAChR
The nAChRs are
ligand-gated ion channels, and, like other members of the "
cys-loop"
ligand-gated ion channel superfamily, are composed of five
protein subunits symmetrically arranged like staves around a barrel. The subunit composition is highly variable across different tissues. Each subunit contains four regions named M1, M2, M3, and M4, which span the membrane and consist of approximately 20 amino acids. The M2 region, which sits closest to the pore lumen, forms the pore lining.
Binding of acetylcholine to the N termini of each of the two alpha subunits results in the 15° rotation of all M2 helices. The cytoplasm side of the nAChR receptor has rings of high negative charge that determine the specific cation specificity of the receptor and remove the hydration shell often formed by ions in aqueous solution. In the intermediate region of the receptor, within the pore lumen,
valine and
leucine residues (Val 255 and Leu 251) define a hydrophobic region which the dehydrated ion must pass through.
nAChR is found at the edges of junctional folds at the
neuromuscular junction on the postsynaptic side, and is activated by acetylcholine release across the synapse. The diffusion of Na
+ and K
+ across the receptor causes depolarization, the end-plate potential, that opens
voltage-gated sodium channels, which allows for firing of the
action potential and potentially muscular contraction.
mAChR
In contrast, the
mAChRs are not ion channels, but belong instead to the superfamily of
G-protein-coupled receptors that activate other ionic channels via a
second messenger cascade.
Role in health and disease
Nicotinic acetylcholine receptors can be blocked by
curare and toxins present in the venoms of
snakes and
shellfishes, like
α-bungarotoxin. Drugs such as the
neuromuscular blocking agents bind reversibly to the nicotinic receptors in the
neuromuscular junction and are used routinely in anaesthesia.
Nicotinic receptors are the primary mediator of the effects of
nicotine. In
myasthenia gravis, the receptor is targeted by
antibodies, leading to muscle weakness.
Muscarinic acetylcholine receptors can be blocked by the drugs
atropine and
scopolamine.
Further Information
Get more info on 'Cholinergic Receptor'.
|
External Link Exchanges
Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:
<a href="http://acetylcholine_receptor.totallyexplained.com">Acetylcholine receptor Totally Explained</a>
Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned. |
