Acetylcholine (ACh) is an organic compound that functions in the brain and body of many types of animals as a neurotransmitter. Its name is derived from its chemical structure: it is an ester of acetic acid and choline. Parts in the body that use or are affected by acetylcholine are referred to as cholinergic.
The adrenergic receptors or adrenoceptors are a class of G protein-coupled receptors that are targets of many catecholamines like norepinephrine (noradrenaline) and epinephrine (adrenaline) produced by the body, but also many medications like beta blockers, beta-2 (β2) agonists and alpha-2 (α2) agonists, which are used to treat high blood pressure and asthma, for example.
Muscarine, L-(+)-muscarine, or muscarin is a natural product found in certain mushrooms, particularly in Inocybe and Clitocybe species, such as the deadly C. dealbata. Mushrooms in the genera Entoloma and Mycena have also been found to contain levels of muscarine which can be dangerous if ingested. Muscarine has been found in harmless trace amounts in Boletus, Hygrocybe, Lactarius and Russula. Trace concentrations of muscarine are also found in Amanita muscaria, though the pharmacologically more relevant compound from this mushroom is the Z-drug-like alkaloid muscimol. A. muscaria fruitbodies contain a variable dose of muscarine, usually around 0.0003% fresh weight. This is very low and toxicity symptoms occur very rarely. Inocybe and Clitocybe contain muscarine concentrations up to 1.6%.
The angiotensin II receptors, (ATR1) and (ATR2), are a class of G protein-coupled receptors with angiotensin II as their ligands. They are important in the renin–angiotensin system: they are responsible for the signal transduction of the vasoconstricting stimulus of the main effector hormone, angiotensin II.
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 nervous system, muscle, and many other tissues of many organisms. At the neuromuscular junction they are the primary receptor in muscle for motor nerve-muscle communication that controls muscle contraction. In the peripheral nervous system: (1) they transmit outgoing signals from the presynaptic to the postsynaptic cells within the sympathetic and parasympathetic nervous system, and (2) they are the receptors found on skeletal muscle that receive acetylcholine released to signal for muscular contraction. In the immune system, nAChRs regulate inflammatory processes and signal through distinct intracellular pathways. In insects, the cholinergic system is limited to the central nervous system.
Muscarinic acetylcholine receptors, or mAChRs, are acetylcholine receptors that form G protein-coupled receptor complexes in the cell membranes of certain neurons and other cells. They play several roles, including acting as the main end-receptor stimulated by acetylcholine released from postganglionic fibers. They are mainly found in the parasympathetic nervous system, but also have a role in the sympathetic nervous system in the control of sweat glands.
A muscarinic agonist is an agent that activates the activity of the muscarinic acetylcholine receptor. The muscarinic receptor has different subtypes, labelled M1-M5, allowing for further differentiation.
The alpha-2 (α2) adrenergic receptor is a G protein-coupled receptor (GPCR) associated with the Gi heterotrimeric G-protein. It consists of three highly homologous subtypes, including α2A-, α2B-, and α2C-adrenergic. Some species other than humans express a fourth α2D-adrenergic receptor as well. Catecholamines like norepinephrine (noradrenaline) and epinephrine (adrenaline) signal through the α2-adrenergic receptor in the central and peripheral nervous systems.
The beta-2 adrenergic receptor, also known as ADRB2, is a cell membrane-spanning beta-adrenergic receptor that binds epinephrine (adrenaline), a hormone and neurotransmitter whose signaling, via adenylate cyclase stimulation through trimeric Gs proteins, increases cAMP, and, via downstream L-type calcium channel interaction, mediates physiologic responses such as smooth muscle relaxation and bronchodilation.
A muscarinic receptor antagonist (MRA), also called an antimuscarinic, is a type of anticholinergic agent that blocks the activity of the muscarinic acetylcholine receptor. The muscarinic receptor is a protein involved in the transmission of signals through certain parts of the nervous system, and muscarinic receptor antagonists work to prevent this transmission from occurring. Notably, muscarinic antagonists reduce the activation of the parasympathetic nervous system. The normal function of the parasympathetic system is often summarised as "rest-and-digest", and includes slowing of the heart, an increased rate of digestion, narrowing of the airways, promotion of urination, and sexual arousal. Muscarinic antagonists counter this parasympathetic "rest-and-digest" response, and also work elsewhere in both the central and peripheral nervous systems.
The human muscarinic acetylcholine receptor M5, encoded by the CHRM5 gene, is a member of the G protein-coupled receptor superfamily of integral membrane proteins. It is coupled to Gq protein. Binding of the endogenous ligand acetylcholine to the M5 receptor triggers a number of cellular responses such as adenylate cyclase inhibition, phosphoinositide degradation, and potassium channel modulation. Muscarinic receptors mediate many of the effects of acetylcholine in the central and peripheral nervous system. The clinical implications of this receptor have not been fully explored; however, stimulation of this receptor is known to effectively decrease cyclic AMP levels and downregulate the activity of protein kinase A (PKA).
The muscarinic acetylcholine receptor M1, also known as the cholinergic receptor, muscarinic 1, is a muscarinic receptor that in humans is encoded by the CHRM1 gene. It is localized to 11q13.
The muscarinic acetylcholine receptor M2, also known as the cholinergic receptor, muscarinic 2, is a muscarinic acetylcholine receptor that in humans is encoded by the CHRM2 gene. Multiple alternatively spliced transcript variants have been described for this gene. It is Gi-coupled, reducing intracellular levels of cAMP.
The muscarinic acetylcholine receptor M4, also known as the cholinergic receptor, muscarinic 4 (CHRM4), is a protein that, in humans, is encoded by the CHRM4 gene.
The alpha-1A adrenergic receptor, also known as ADRA1A, formerly known also as the alpha-1C adrenergic receptor, is an alpha-1 adrenergic receptor, and also denotes the human gene encoding it. There is no longer a subtype α1C receptor. At one time, there was a subtype known as α1C, but it was found to be identical to the previously discovered α1A receptor subtype. To avoid confusion, the naming convention was continued with the letter D.
The alpha-1B adrenergic receptor (α1B-adrenoreceptor), also known as ADRA1B, is an alpha-1 adrenergic receptor, and also denotes the human gene encoding it. The crystal structure of the α1B-adrenergic receptor has been determined in complex with the inverse agonist (+)-cyclazosin.
Prostaglandin F receptor (FP) is a receptor belonging to the prostaglandin (PG) group of receptors. FP binds to and mediates the biological actions of Prostaglandin F2α (PGF2α). It is encoded in humans by the PTGFR gene.
Potassium voltage-gated channel subfamily A member 2 also known as Kv1.2 is a protein that in humans is encoded by the KCNA2 gene.
G protein-coupled receptor kinase 5 is a member of the G protein-coupled receptor kinase subfamily of the Ser/Thr protein kinases, and is most highly similar to GRK4 and GRK6. The protein phosphorylates the activated forms of G protein-coupled receptors to regulate their signaling.
4-DAMP (1,1-dimethyl-4-diphenylacetoxypiperidinium iodide) is a selective muscarinic acetylcholine receptor (mAChR) M3 antagonist. It is also able to antagonize M1 receptors but "prefers" M3. It competitively binds to the acetylcholine binding site on mAChRs, causing right-ward shift in the dose response curves for mAChR agonists.
