CHOLINERGIC RECEPTORS
TYPES OF CHOLINERGIC RECEPTORS:
- 2 major types: Nicotinic & muscarinic receptor.
NICOTINIC RECEPTOR:
- NM: Skeletal muscle endplate
- NN: Ganglionic cells, adrenal medulla, CNS.
- Acetylcholine acts on nicotinic receptors produces contraction of skeletal muscle.
Drugs:
- D-tubocurarine – Skeletal muscle relaxant.
- Acts by competitive inhibition of NM receptors at neuron-muscular junction.
Bupropion –
- Nicotinic receptor antagonist
Clinical:
- In Myasthenia gravis, antibodies are present against nicotinic receptor.
- Dry mouth during antidepressant therapy is caused by blockade of muscarinic acetylcholine receptors.
II) MUSCARINIC RECEPTORS:
- Cholinergic receptors on muscle endplate are cation channels.
- Selectively stimulated by muscarine & blocked by atropine.
- Located primarily on autonomic effector cells of heart, smooth muscles, respiratory tract & CNS.
- Subtypes:
- M1 ,M2, M3, M4 & M5.
- Muscarinic antogonists decreases gastric & respiratory secretions, fascilitates AV conduction.
- Oxybutynin – Muscarinic receptor inhibitor.
Clinical:
- Drug used for muscarinic symptoms seen in cobra envenomation is Neostigmine.
RELATED DRUGS & THEIR RECEPTORS
| Drug | Nm | Nn | M1 | M2 | M3 |
|---|---|---|---|---|---|
| ACh, Carbachol(maximum nicotinic effect), Methacholine, AChEi (Physostigmine, Galantamine, Neostigmine, Pyridostigmine) | + | + | + | + | + |
| Nicotine, Varenicline | + | + | |||
| Succinylcholine | +/- | ||||
| Atracurium, Vecuronium, Tubocurarine, Pancuronium | – | ||||
| Epibatidine, DMPP | + | ||||
| Trimethaphan, Mecamylamine, Bupropion, Dextromethophan, Hexamethonium | – | ||||
| Muscarine, Oxotremorine, Bethanechol, Pilocarpine | + | + | + | ||
| Atropine, Tolterodine, Oxybutynin | – | – | – | ||
| Vedaclidine, Talsaclidine, Xanomeline, Ipatropium | + | ||||
| Pirenzepine, Telenzepine | – | ||||
| Methoctramin | – | ||||
| Darifenacin, 4-DAMP, Darifenacin, Solifenacin | – |
Exam Important
- Action potentials on the alpha motor neuron release acetylcholine (Ach) from the axon terminal
- Cholinergic receptors on the muscle endplate are cation channels
- Alpha motor neurons excite, and Renshaw cells inhibit, the muscle endplate
- In Myasthenia gravis, antibodies are present against Nicotinic Receptor
- Nicotine receptor sites include Adrenal medulla, Skeletal muscle & Sympathetic ganglia
- Carbachol has maximum nicotinic effect
- Muscarinic antogonists Decrease gastric secretions, Decrease respiratory secretions & Fascilitates AV conduction
- Oxybutynin acts by Muscarinic receptor inhibition
- D-tubocurarine is a skeletal muscle relaxant that acts by competitive inhibition of NM receptors at neuron-muscular junction.
- Dry mouth during antidepressant therapy is caused by blockade of Muscarinic acetylcholine receptors
- Bupropion is Nicotinic receptor antagonist
- Drug used for muscarinic symptoms seen in cobra envenomation is Neostigmine
- Acetylcholine acting on nicotinic receptors produces Contraction of skeletal muscle
- Nicotinic cholinergic receptors are ionic channel
- Varenicline acts by Partial nicotine receptor agonist
- Muscarinic cholinergic receptors are seen at Stomach, CNS , Glands
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