PNS Flashcards
Botulinum Toxin
C-terminus of heavy chain binds to ganglioside and complex is endocytosed. N-terminus translocates light chain from endosomal lumen to cell cytoplasm by making a channel in the endosomal membrane. Light chain is metallopeptidase and cleaves target SNARE in cytoplasm
Tetanus Neurotoxin
C-terminus if heavy chain binds to ganglioside enabling endocytosis. Toxin moves towards soma of motor neuron by retrograde atonal transport, and gets discharged into intersynaptic space. Binds to presynaptic membrane of inhibitory neurons and is endocytosed. Acidic nature of vesicles causes insertion of N-terminus light chain into cytoplasm where it cleaves synaptobrevin
Alpha-latrotoxin
Ca independent endocytosed by binding to neurexins and CL1. Binding leads to formation of a Ca permeable pore within the presynaptic membrane allowing Ca influx and trigger transmitter release
Hemicholinium
Inhibits choline transporter (ChT) that co-transports sodium
Trierhylcholine
Competes with choline as a substrate of ChAT and gets converted to acetyltriethylcholine which is release in place of ACh. False transmitter
Vesamicol
Non-competitive and reversible antagonist of VAChT
Beta-bungarotoxin
Bind to and block shaker-type K channels. Subsequent block of ACh release is probably via its PLA2 activity which degrades active zone lipids
Alpha bungarotoxin
Irreversible antagonist of the adult Nm and inhibitor of (alpha7)5 Nn in the brain
Decamethonium
Depolarising blocker of adult Nm
Trimetaphan
Competitive antagonist of ganglionic nAChRs
Hexamethoniun
Use-dependent antagonist of ganglionic nAChRs. It is therefore likely to cause an open channel block. This action shortens the duration of current flow because the open channel either becomes occluded or closes
Suxamethonium
Depolarising muscle relaxant (hydrolysed by plasma cholinesterase)
d-tubocurarine
Non-depolarising blocking agent of No, but poor selectivity between ganglionic and NMJ types of nAChRs. Induces histamine release from mast cells causing transient hypotension
Atracurium
Non-depolarising blocking agent at NMJ. Quaternary ammonium compound so poorly absorbed. Induced histamine release so causes transient hypotension. Unstable at physiology pH and so spontaneously breaks down in plasma
Pancuronium
Non-depolarising blocking agent at NMJ. Inhibits muscarinic receptors and this induces mild tachycardia
Nicotine
nAChR agonist. Stimulates them blocks autonomic ganglia. Stimulates CNS. tertiary amine
Varenicline
Partial agonist for Nn nAChR. Stimulate some dopamine release in mesolimbic dopaminergic pathway, helping to alleviate some nicotine withdrawal symptoms. Full agonist on (alpha7)5 receptor
Carbachol (carbamylcholine), Bethanechol
Muscarinic agonist - choline ester. Longer duration of action the ACh
Pilocarpine
Muscarinic agonist - naturally occurring cholinomimetic alkaloid. Longer duration of action that ACh as stable to hydrolysis by AChE. Treat glaucoma - contracts ciliary muscle to produce traction on the trabecular meshworkbaround the Schlemm canal causing an immediate drop in intraoccular pressure as a result of increased drainage of aqueous humour. Rapid miosis
Cevimeline
M3 selective agonist used to increase salivation and lacrimation (Sjögren’s syndrome)
Atropine
Antimuscarinic agent. Pupil dilation
Ipratropium
Semisynthetic derivative of atropine. Antimuscarinic agent
Pirenzepine
Synthetic antimuscarinic agent. M1 selective
Darifenacin
Synthetic antimuscarinic agent. Selective inhibition of m3 receptors that mediate contraction of detrusor muscle - treatment of urinary incontinence
Tropicamide
Short acting antimuscarinic agent. Pupil dilation
Edrophonium
Non covalent short acting inhibitory of AChE. Quaternary ammonium compound. Binds to catalytic anionic site of the enzyme. Used to diagnose myasthenia gravis.