B.1- cholinergic transmission Flashcards
agents causing presynaptic inhibitory effect
𝝰₂ M₂ Hemicholinium Vesamicol Botulinum toxin
agents causing presynaptic stimulatory effect
M₁ B₂ AT₁ 4-Aminopyridine Latrotoxin (spider venom)
what are the function of Acetylcholine (Ach) in the synaptic cleft?
- activation of postsynaptic receptors (physiological effect)
- activation of presynaptic autoreceptors
- rapid degradation by acetylcholinesterase
what does Hemicholinium do?
inhibits transport of choline into the nerve terminal`
what does Vesamicol do?
inhibits transport of Ach into storage vesicles
what does Botulinum toxin do?
inhibits the release of Ach- loaded vesicles (interfere with SNARE proteins)
indications for Botulinum toxin
Blepharospasm (abnormal blinking)
Hyper- hydrosis (↑ sweating)
dystonia (twisting movement)
cosmetics
where can we find Latrotoxin?
in spider venom
function of 4-aminopyridine
inhibits K channels–> depolarization–> excitatory signal–> neurotransmitter release
function of Latrotoxin
creates pores along the membrane–> Ca² influx–> excitatory signal–< neurotransmitter release
name the cholinergic receptors and their mechanism of action
muscarinic receptors: "qiq" M1- Gq coupled M2-Gi coupled M3- Gq coupled nicotinic (Na-K ion channels): Neural (Nn) Muscular (Nm)
where is M1 found and what is the effect
nerve endings
↑ gastric acid secretion
where is M2 found and what is the effect
heart
inhibits cardiac activity
where is M3 found and what is the effect
smooth muscle, endothelial cells, glands
bronchoconstriction, GI secretions and motility associated with digestion
where is Nn found and what is the effect
ANS ganglia, adrenal medulla
activation of sympathetic and parasympathetic nerves
where is Nm found and what is the effect
Neuromuscular end plates
causes excitatory post-synaptic potential (EPSP)
synthesis of Ach
ChAT - Choline Acetyltransferase converts Acetyl-coA + Choline into Ach in the nerve terminal
storage of Ach
Ach is transported into the vesicle via VAT- vesicle-associated transporter
*inhibited by vesmicol
Release of Ach
Ca² influx induces action potential–>Ach is released into the synaptic cleft
*inhibited by botulinum toxin
Reception and Recognition of Ach
Ach acts on muscarinic and nicotinic receptors on the postsynaptic cell, and some presynaptic receptors on neurons
Termination of Ach
Acetylcholinesterases or pseudocholinesterase hydrolyze Ach into choline and acetate
Ach recycling
Ach is taken back up into the neuron through presynaptic receptors
*rate-limiting step
cholinergic effects on the eye
miosis ↑M3 mydriasis ↓M3 accommodation ( ↑M3--> contracted ciliary muscle) ↓ of intraocular pressure ↑ lacrimation
cholinergic effects on the blood vessels
constriction of coronary a.
