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Biochemical events at a cholinergic synapse. Choline is transported into the presynaptic nerve terminal by a Na+-dependent choline transporter (CHT),
which can be blocked by the drug hemicholinium. Acetylcholine (ACh) is synthesized from choline and acetyl Co-A (AcCoA) by the enzyme choline
acetyltransferase (ChAT) in the cytoplasm. ACh is then transported from the cytoplasm into vesicles by the vesicle-associated transporter (VAT) along with
peptides (P) and adenosine triphosphate (ATP). This step can be blocked by the drug vesamicol. ACh is released from the nerve terminal when voltagesensitive Ca2+ channels open, allowing an influx of Ca2+, which leads to fusion of vesicles with the surface membrane and expulsion of ACh and cotransmitters into the synaptic cleft. This process involves synaptosome-associated proteins (SNAPs) and vesicle-associated membrane proteins (VAMPs)
Source: Chapter 7. Neurotransmitters & Neuromodulators, Ganong's Review of Medical Physiology, 24e
and can be prevented by the drug botulinum toxin. The released ACh can act on muscarinic G protein-coupled receptors on the postsynaptic target (eg,
Citation:
KE,ionotropic
Boitano S,
Barman in
SM,
Brooks HL.
Ganong's
of Medical
Physiology,
24e;shown).
2012 Available
at: http://mhmedical.com/
smooth muscle)
or onBarrett
nicotinic
receptors
autonomic
ganglia
or theReview
endplate
of skeletal
muscle (not
In the synaptic
junction, ACh is
Accessed:
May
12,
2017
readily metabolized by the enzyme acetylcholinesterase. Autoreceptors and heteroreceptors on the presynaptic nerve ending modulate neurotransmitter
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release.