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Aceytlcholine
Synthesis to inactivation
36
Pharmacology
Undergraduate 2
01/17/2017

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Term
Who discovered ACh?
Definition
Otto Loewi in 1926
Term
What is ACh?
Definition
quaternary amine with a low molecular mass serving as a neurotransmitter in CNS and
Term
Examples of cholinergic sites in the CNS?
Definition
synapse in the ganglia of the visceral motor systems
- ACh is the CNS is still not fully understood
Term
Where is ACh synthesized?
Definition
in the nerve terminal
Term
What is the rate limiting factor of ACh synthesis?
Definition
availability of Choline and Aceytl CoA
Term
Where is Choline obtained from?
Definition
Either from plasma or by metabolism of choline-containing compounds, obtained from egg yolk, liver and vegetables in our diets
Term
What is the concentration of Choline in the plasma?
Definition
10µm
Term
How much of Choline is recycled?
Definition
50%
Term
What is Aceytl CoA synthesized from?
Definition
Glucose
Term
Which enzyme catalyzes the synthesis of ACh?
Definition
Choline acetyltransferase (ChAT).
- This enzyme is synthesized in the soma and found in high concentration at the nerve terminal
Term
What stops overproduction of ACh?
Definition
ChAt enzyme is subject to feedback production inhibition where ACh bind to the allosteric site signalling it to stop overproduction of ACh.
Term
Where is ACh stored?
Definition
In Vesicles
Term
What transports the ACh into the vesicles?
Definition
transport protein called Vesicular Acetylcholine transporter (VAChT)
Term
How many molecules of ACh does VAChT stock up into vesicles?
Definition
10,000 molecules of ACh in cholinergic vesicles.
Term
What mechanism does Vesicular Acetylcholine transporter (VAChT) use?
Definition
This pump is driven by a proton pumping ATPase.
(1 H+ out in exhange of 1 NT in driven by hydrolysis of ATP)
Term
Is ACh subject for reuptake?
Definition
No
Term
What inactivates ACh in the nerve terminal ?
Definition
Hydrolytic enzyme Acetylcholinesterase
Term
What does Hydrolytic enzyme Acetylcholinesterase do?
Definition
Hydrolyses ACh into acetate and choline
Term
What is the speed of catalytic activity for AChE?
Definition
5000 molecules of ACh per AChE molecule per second
Term
How is choline reuptaken by neurons?
Definition
via the Choline Transporter
Term
How does the Choline transporter work?
Definition
1 Choline in - exchange of 1 Na out
Term
Which receptors does ACh bind to?
Definition
mAChR
and nAChR
Term
What are the two types of nicotinic AChR
Definition
- neuromuscular nAChR
- neuronal nAChR
Term
What is the difference between neuromuscular nAChR and neuronal nAChR?
Definition
They both contain 5 sub units but
neuromuscular nAChR contains 2α : 1ß : 1δ : 1ε
neuronal nAChR contains 3α: 2ß
Term
Which sub-unit contains the binding site for ACh?
Definition
α - subunit
Term
Which ACh receptor is more common in the brain?
Definition
mAChR
Term
Describe the structure of mAChR
Definition
- 7 helical membrane span proteins
- ACh binding site available on the extracellular surface
Term
What are the 5 subtypes and which G- proteins are they coupled to?
Definition
M1 - Gq
M2 - Gi
M3 - Gq
M4 - Gi
M5 - Gq
Term
Where is mAChR highly expressed?
Definition
Striatum and other forebrain regions
Term
What effect do they have in the striatum?
(Think Samits lecture)
Definition
Activate inward rectifying K+ channels and Ca activated K+ channels --> results in inhibitory influence on dopamine mediated motor effects
Term
How does Botulinum affect cholinergic transmission?
Definition
Blocks release of ACh; causes muscular paralysis
Term
How does Vesamicol affect cholinergic transmission?
Definition
blocks vesicular ACh transporter - unable to pack ACh into vesicles therefore less available in stores at the terminal - reducing ACh release
Term
How does Hemicolinium affect cholinergic transmission?
Definition
decrease synthesis of ACh by decreasing reuptake of Choline by binding to the Choline transporter
Term
How can cholinergic neurons be located?
Definition
By staining markers of cholinergic neurons including ChaT and AChE
Term
Why is AChE an unreliable marker?
Definition
Enyzme is not present in the neuron but is densly concentrated in the synpatic cleft
Term
Why is ChAT a reliable marker ?
Definition
Selectively lables cholinergic neurons
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