Chemistry Reference
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Synaptic cleft
Presynaptic
membrane
Postsynaptic
membrane
AcCH
release
Cholinergic receptors
Ve sicles containing
acetyl choline
Acetyl cholinesterase
bound to membrane
Direction of neurotransmission
fIgure 10.4
Diagram of cholinergic synapse.
BOX 10.2 antIdOteS tO CHOlIneSteRaSe pOISOnInG
By ORGanOpHOSpHORuS InSeCtICIdeS
Because of the high human risks associated with both OP insecticides and the
related nerve gases, antidotes have been developed to counteract poisoning by
them. Basically, these are of two different kinds:
1. Reactivators of phosphorylated ChE. Pyridine aldoxime methiodide
(PAM) and related compounds are the best known. They reactivate
the phosphorylated enzyme so long as aging has not occurred. They
do not, however, reactivate the aged enzyme. ChE which has been
phosphorylated by certain nerve gases ages rapidly!
2. Atropine acts as an antagonist of acetylcholine at muscarinic recep-
tors, but not at nicotinic receptors. By acting as an antagonist, it
can prevent overstimulation of muscarinic receptors by the exces-
sive quantities of acetylcholine remaining in the synaptic cleft when
AChE is inhibited. The dose of atropine needs to be carefully con-
trolled because it is toxic.
Antidotes are administrated to patients after there has been exposure to
OPs. They are also sometimes given as a protective measure when there is a
risk of exposure, for example, to troops fighting in the Gulf War. Of the two
types of antidote mentioned earlier, only atropine is effective against carba-
mate poisoning.
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