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Summary Pharmacology (Ulens)

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Summary of all classes of Ulens.

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  • 26 januari 2022
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Part 2: drugs affecting cholinergic transmission
H1: Cholinergic transmission
Synaptic transmission is the communication language in CNS and PNS
2 parts

• Electrical component: carried by AP
• Chemical component

Electrical component
AP: transmembrane voltage in mV as a function of time (sec). 3 parts TEKENING
→ 1st part: depolarization phase. Ion channels selective for Na will permeate through the mbr. Ion
channels will open. Na C is much bigger on outside. Electrochemical force will be inward, so Na
comes in. Mbr voltage will become less negative. No E required.
→ 2nd phase: repolarization phase. Carried by K ions. C K is bigger intracellularly. K ion channels will
open and permeate K along the C gradient. More + ions leave so mbr voltage becomes negative
again. No E required.
→ 3rd phase: hyperpolarization phase. More + ions left so mbr voltage becomes negative again. More
than resting mbr potential.
As a result of each AP net influx of Na+ → needs to get back out: intrinsic mbr protein that pumps out
Na and K in. Requires E (ATP) → Na-K-pump or Na-K-ATPase.

AP propagates along the nerve terminal until it reaches its terminus
→ chemical component takes over.
Vesicles loaded with NT will fuse with the presynaptic mbr = process that involves Ca and SNARE
proteins. The NT are released into the synaptic cleft, diffuse through it and then bind on postsynaptic
receptors where AP is generated.

 Interplay between chemical and electrical component.




Important slide: subdivision of nervous system.

H1: drugs on peripheral nervous system (right)

Later chapters: drugs on the CNS (left).

CNS is also divided into parts of the PNS.
PNS: efferent, OS, PS.
BBB = collection of tissues and BV that forms a
physical barrier for the permeation of drugs into
the CNS. Very lipophilic boundary (so drugs that
have a very lipophilic character).


Efferent somatic system:
Neurons that originate from the CNS make a synaps with the muscle. Specific NT: nAch.

,OS:
Neurons that make a synaps with BV. NT: NA (noradrenaline). Specific NT: mAch.

PS:
Targets salivary glands. Specific NT: mAch.

Ach receptors:

• Activation by nicotine
• Activation by muscarine




Choline: 4ary nitrogen, means that
NT is permanently + charged
→ relatively polar mol.

Ach = synthesized under influence
of CAT (choline acetyl transferase):
enzyme that transfers an acetyl
group onto choline (one step
synthesis).
→ choline converted into Ach
→ Ach concentrated into vesicles
→ will be released in synaptic cleft
when AP reaches its terminus
Very important that NT is eliminated from the synapse otherwise the postsynapt R will stay occupied
by the NT
→ desensitization (unresponsive to new pulse of Ach)
→ specific enzyme for Ach on postsyn mbr: acetylcholinesterase
→ does the reverse reaction of CAT
→ choline recycled to a choline carrier = transport protein

nAchR: pentamer with central pore in mbr
→ selective for cations
→ ligand gated ion channel
→ ligand binding site located at interphases between each
subunit (5 interphases)
→ binding causes conformational change that opens pore
→ permeates cations
→ creates AP
→ excitatory ligand gated receptor
mAchR: GPCR → 7 transmembrane domains
Funnel shape where the muscarine or NT are bound
→ 1 single binding site (itt 5 in nAchR)
→ Rely on intracell G proteins for their signal transduction
→ Couples to Gi (inhibitory) protein
→ End result of signaling of mAch leads to decrease of C of cAMP

,Ach binds to mAchR
→ conformation change
→ activation Gi protein (orange = alfa subunit, blue = beta, green = gamma)
→ GDP will be released and replaced by GTP
→ complex will dissociate into alfa and b-g subunit. Alfa targets adenylylcyclase (synthesizes cAMP)
→ decrease cAMP concentration


Gq → q means that R signals through IP3 and Ca2+ (not
cAMP)




Muscle type: heteropentameric.
→ You need all 5 different subtypes for it to be
functional

Class II: most abundant subtypes in the brain: alfa 7
homopentameric receptor

Class III: heteropentameric

, Negative chronotropic
effect: decrease of heart
rate due to decrease of
AP firing

Negative dromotropic
effect: decrease of heart
rate due to decrease of
AP firing by pacemaker
cells in the AV node




Disease in which patients raise Ab against their own
muscle nicotinic R.
L: Fab fragment of Ab of patient.
Fab region of an Ab = Ag binding region.
Ab attacks a very specific region in alfa subunit of
muscle type R: MIR = Main Immunogenic Region.
Binding of Ab to alfa subunit will make R dysfunctional
→ main symptom = muscle weakness
→ drugs that activate nAchR

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