Cholinoreceptors Flashcards
What are the types of cholinergic receptors according to their affinity to ligands?
M&N cholinergic receptors
what are M Cholinergic receptors?
- They are muscarinic receptors which are selectively activated by muscarine and can be blocked by atropine.
- They are also metabotropic receptors which are coupled with G-proteins.
what are N Cholinergic receptors?
- They are nicotinic receptors which are selectively activated by small doses of nicotine and blocked by high doses of nicotine.
-They are ionic receptors Which need 2 acetylcholine molecules to bind to each receptor to be able to open them.
What type of M1 Cholinergic receptors do we have?
Neuronal with a postsynaptic location
What type of M2 Cholinergic receptors do we have?
- Postsynaptic or cardiac
- Presynaptic
What type of M3 Cholinergic receptors do we have?
- Postsynaptic or glandular
- extra synaptic
What is the transduction mechanism of M1 Cholinergic receptors?
They couple with Gq proteins which activate force for lipase C in turn activating the secretion of DG and IP3 leading to an increase of calcium quantity which as a result we have a stimulatory action.
Where can we find M1 Cholinergic receptors?
- CNS, limbic system, reticular formation, and basal ganglion
- autonomic ganglia
- enterochromaffin cells
what is the action of M1 Cholinergic receptors in CNS?
Activation and regulation of psychomotor activity as well as activation of weakening reactions and learning process
what is the action of M1 Cholinergic receptors in autonomic ganglia?
Depolarization and development of slow EPSP
what is the action of M1 Cholinergic receptors in enterochromaffin cells?
Stimulation of the secretory function through the release of histamine
What is the transaction mechanism of M2 Postsynaptic Cholinergic receptors?
They couple with Gi proteins at which they lead to the inactivation of adenylate cyclase and decrease of cyclic AMP quantity as a result inhibitory action is developed
Where can we find post synaptic M2 Cholinergic receptors?
- SA node
- Atriums
- AV node
- ventricular muscle
what is the action of post synaptic M2 Cholinergic receptors on the SA node?
It decreases the frequency of spontaneous diastolic depolarization leading to bradycardia
what is the action of post synaptic M2 Cholinergic receptors on the atriums?
It shortens the potential action duration in atrial muscle leading to the decrease in contractility of atrial muscle
what is the action of post synaptic M2 Cholinergic receptors on the AV node?
Decrease in AV conduction
what is the action of post synaptic M2 Cholinergic receptors on the ventricular muscle?
Insignificant decrease in ventricular contraction
what is the action of presynaptic M2 Cholinergic receptors?
They have a regulatory role at which their stimulation inhibits the release of acetylcholine from the presynaptic membrane
What is the transduction mechanism of post synaptic M3 receptors?
They are coupled with Gq protein
where can we find post synaptic M3 receptors?
Smooth muscles and exocrine glands
What is the effect of postsynaptic M3 receptors on smooth muscles?
- The constriction of pupillary constrictor muscle leading to a reduction in pupil size and miosis
- contraction of ciliary muscle leading to the relaxation of ligament of Zen and increase in length curvature leading to spasm of accommodation which causes near vision
- reduction of intraocular pressure due to tension on the trabecular meshwork opening its spores and facilitating the outflow of aqueous humor into the canal of Schlemm
- bronchospasm
- increase in peristalsis of the GIT
- relaxation of sphincters
- increase in tone of biliary tracts
- increase in tone of urinary tract and constriction of bladder
- contraction of uterus
What is the effect of postsynaptic M3 receptors on exocrine glands?
Lacrimation, sweating, salivation, increased bronchial secretion, and increased stomach juice secretion
Describe the extra synaptic M3 receptors.
- They are coupled with GQ proteins
- they are mainly located on the endothelial cells of vasculature
- they lead to the production of NO or endothelium derived relaxing factor which relax smooth muscles and dilate vessels
What are the similarities and differences between the transduction mechanisms of different muscarinic receptors?
M1, M3, and M5 couple with Gq proteins, whereas M2 and M4 receptors coupled with Gi proteins.
Where can we find Nn receptors?
- Post synaptic
- presynaptic
what is the role of presynaptic Nn receptors?
They have a regulatory role at which their stimulation augments release of acetylcholine from the presynaptic membrane.
Where can we find post synaptic Nn receptors?
- CNS in cerebral cortex,medulla oblongata, neurohypothesis, Renshaw cells of the spinal cord
- Autonomic ganglia
- adrenal medulla
- carotid sinus
What is the action of Nn receptors on the CNS?
- Control of physical and motor functions
- wakefulness and learning
- increased release of ADH from neurohypophysis
What is the action of Nn receptors on the Autonomic ganglia?
Increases the frequency of impulse conduction
What is the action of Nn receptors on the adrenal medulla?
Enhances the secretion of epinephrine and norepinephrine
What is the action of Nn receptors on the carotid sinus?
Reflex stimulation of respiratory and vasomotor center
Describe Nm receptors.
They are located in neuromuscular synapse causing depolarization of the endplate and contraction of skeletal muscles
What is the action of hemicholinum?
It inhibits the synthesis of acetylcholine by inhibiting the action of sodium dependent membrane transporter which participates in the transport of choline. It inhibits the synthesis of acetylcholine
What is the action of vesamicol?
It inhibits the transporter which transports acetylcholine from axoplasm into the vesicles at which it disturbs the vesicular transport and storage of acetylcholine
what is the action of botulinum toxin?
It disturbs the release of acetylcholine into the synaptic cleft by interacting with the synaptic vesicles membrane protein called synaptobrevin
