The cholinergic system is based on the neurotransmitter acetylcholine (ACh), firstly recognized by Loewi in 1920s and found widely distributed in both central and peripheral nervous systems. The two basic types of acetylcholine receptors in the nervous system and at neuromuscular junctions are: muscarinic acetylcholine receptors (mAChR) and nicotinic acetylcholine receptors (nAChR). Acetylcholine receptors are also found expressed in multiple cells including endothelial and immune system cells.
Cholinesterases are a family of enzymes that katalyse the hydrolysis of ACh into choline and acetic acid, an essential process allowing for the restoration of the cholinergic neuron. Cholinesterases are divided into two: acetylcholinesterase (AChE; EC 188.8.131.52.) and butyrylcholinesterase (BuChE; EC 184.108.40.206). AChE participates in cholinergic neurotransmission by hydrolyzing acetylcholine. It is expressed in nerve and blood cells. Compared to AChE, the importance of BuChE is not well understood. BuChE was known as plasmatic cholinesterase or pseudocholinesterase. Similarly, AChE was called blood, also erythrocytal cholinesterase as its activity remains in the cell mass after blood centrifugation. The name AChE derives from the natural substrate acetylcholine as opposed to BuChE that has no natural substrate. An absence or mutation of BuChE leads to a medical condition (see below) that shows itself only in the presence of some drugs (e.g. succinylcholine) and toxins (e.g. cocaine), due to its ability to split artificial substrates.
This article is published online in Biomedical papers of the Medical Faculty of the University Palacký, Olomouc, Czech Republic and is free to access online.