Muscle Type Nicotinic Receptor
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The muscle-type nicotinic receptor is a type of
nicotinic acetylcholine receptor Nicotinic acetylcholine receptors, or nAChRs, are receptor polypeptides that respond to the neurotransmitter acetylcholine. Nicotinic receptors also respond to drugs such as the agonist nicotine. They are found in the central and peripheral ne ...
consisting of the subunit combination (α1)2β1δε (adult receptor) or (α1)2β1δγ (fetal receptor). These receptors are found in
neuromuscular junctions A neuromuscular junction (or myoneural junction) is a chemical synapse between a motor neuron and a muscle fiber. It allows the motor neuron to transmit a signal to the muscle fiber, causing muscle contraction. Muscles require innervation to ...
, where activation leads to an excitatory postsynaptic potential (EPSP), mainly by increased Na+ and K+ permeability.


Activation

Tetraethylammonium (TEA) is a molecule found to be a weak
agonist An agonist is a chemical that activates a receptor to produce a biological response. Receptors are cellular proteins whose activation causes the cell to modify what it is currently doing. In contrast, an antagonist blocks the action of the ago ...
of the muscle‐type nicotinic receptor. Since receptor activation occurs as isolated bursts, it has been proposed that the receptors have a very low channel‐opening rate constant when bound to TEA.


Inhibition

Lidocaine Lidocaine, also known as lignocaine and sold under the brand name Xylocaine among others, is a local anesthetic of the amino amide type. It is also used to treat ventricular tachycardia. When used for local anaesthesia or in nerve blocks, lidoca ...
, a
local anesthetic A local anesthetic (LA) is a medication that causes absence of pain sensation. In the context of surgery, a local anesthetic creates an absence of pain in a specific location of the body without a loss of consciousness, as opposed to a general an ...
, has multiple inhibitory actions on the receptor and analysis of the structure of lidocaine has identified the presence of a hydrophobic aromatic ring and a hydrophilic terminal amine. Diethylamine (DEA), a molecule that mimics the hydrophilic moiety of lidocaine by way of a positively charged amine, has been found to block the channel when the receptor is open restricting the flow of Na+ and K+ ions. 2,6- Dimethylaniline (DMA), a molecule that mimics the hydrophobic moiety of lidocaine, has been found to bind the receptor at inter-subunit crevices of the trans-membrane spanning domain thereby causing non-competitive inhibition and restricting the channel from opening.
Benzocaine Benzocaine, sold under the brand name Orajel amongst others, is an ester local anesthetic commonly used as a topical pain reliever or in cough drops. It is the active ingredient in many over-the-counter anesthetic ointments such as products f ...
and
tetracaine Tetracaine, also known as amethocaine, is an ester local anesthetic used to numb the eyes, nose, or throat. It may also be applied to the skin before starting an intravenous (injection) to decrease pain from the procedure. Typically it is applied ...
are also
local anesthetics A local anesthetic (LA) is a medication that causes absence of pain sensation. In the context of surgery, a local anesthetic creates an absence of pain in a specific location of the body without a loss of consciousness, as opposed to a general an ...
that have an inhibitory effect on the muscle‐type nicotinic receptor.
Benzocaine Benzocaine, sold under the brand name Orajel amongst others, is an ester local anesthetic commonly used as a topical pain reliever or in cough drops. It is the active ingredient in many over-the-counter anesthetic ointments such as products f ...
is a permanently uncharged species that inhibits the receptor by plugging the pore of the opened channel.
Tetracaine Tetracaine, also known as amethocaine, is an ester local anesthetic used to numb the eyes, nose, or throat. It may also be applied to the skin before starting an intravenous (injection) to decrease pain from the procedure. Typically it is applied ...
is a permanently positively charged species. It can bind to the receptor at different sites in both the open and closed conformations. Both of these local anesthetics enhance nAChR desensitization.


Ligands


Agonist

*
Acetylcholine Acetylcholine (ACh) is an organic chemical that functions in the brain and body of many types of animals (including humans) as a neurotransmitter. Its name is derived from its chemical structure: it is an ester of acetic acid and choline. Part ...


Partial Agonists

*
Carbachol Carbachol, also known as carbamylcholine and sold under the brand name Miostat among others, is a cholinomimetic drug that binds and activates acetylcholine receptors. Thus it is classified as a cholinergic agonist. It is primarily used for var ...
*
Suxamethonium Suxamethonium chloride, also known as suxamethonium or succinylcholine, or simply sux by medical abbreviation, is a medication used to cause short-term paralysis as part of general anesthesia. This is done to help with tracheal intubation or ele ...


Antagonists

* α-Bungarotoxin *
α-Conotoxin A conotoxin is one of a group of neurotoxic peptides isolated from the venom of the marine cone snail, genus ''Conus''. Conotoxins, which are peptides consisting of 10 to 30 amino acid residues, typically have one or more disulfide bonds. Cono ...
*
Hexamethonium Hexamethonium is a non-depolarising ganglionic blocker, a nicotinic ( nAChR) receptor antagonist that acts in autonomic ganglia by binding mostly in or on the nAChR receptor, and not the acetylcholine binding site itself. It does not have a ...
*
Pancuronium Pancuronium (trademarked as Pavulon) is an aminosteroid muscle relaxant with various medical uses. It is used in euthanasia and is used in some states as the second of three drugs administered during lethal injections in the United States. Mecha ...
*
Tubocurarine Tubocurarine (also known as ''d''-tubocurarine or DTC) is a toxic alkaloid historically known for its use as an arrow poison. In the mid-1900s, it was used in conjunction with an anesthetic to provide skeletal muscle relaxation during surgery or ...


See also

*
Nicotinic acetylcholine receptor Nicotinic acetylcholine receptors, or nAChRs, are receptor polypeptides that respond to the neurotransmitter acetylcholine. Nicotinic receptors also respond to drugs such as the agonist nicotine. They are found in the central and peripheral ne ...
*
Ganglion type nicotinic receptor The alpha-3 beta-4 nicotinic receptor, also known as the α3β4 receptor and the ganglion-type nicotinic receptor,Pharmacology, (Rang, Dale, Ritter & Moore, , 5th ed., Churchill Livingstone 2003) p. 138. is a type of nicotinic acetylcholine receptor ...


References

Nicotinic acetylcholine receptors {{biochemistry-stub