Cholinergics Flashcards
hemicholinium
blocks choline transport into the terminal, not pharmacologically useful because it blocks all cholinergic functions
choline cotransports
with Na+, rate limiting step
CAT
choline + acetylCoA –> Ach inhibitors are not effective
ACh is stored
in presynaptic vesicles
ACh structure
quarternary amine, positively changed, has an ester bond prone to rapid degredation
uptake
- choline 2. ACh synthesis, 3. vesicle storage
black widow
alpha latrotoxin, causes over release of ACh
botulinum toxin
blocks Ach release
release of ACh
basic depolarization-induced excretion-secretion coupling (calcium dependent vesicle fusion with pre synaptic membrane)
botox is used for
strabismus, blapharospasm, hyperhidriosis, focal distonia, migraine, cosmetic treatment
d-tubocurarine function
blocks nicotinic receptors (non-depolarizing neuromuscular blocker)
cholinomimetic
cholinergic agonist ‘mimicry’
botulinum neurotoxins
7 types of protease, cleave VAMP/SNAP-25/syntaxin (proteins required for fusion and exocytosis of ACh synaptic vesicles)
botulinum neurotoxins have selective
activity at NMJ and cause flaccid paralysis, effects last for weeks and cause muscle atrophy
botulinum neurotoxin precaution
systemic spread can block crucial functions such as respiration
removal of ACh
flashlike suddeness, shorter than time to make an action potential (you’ve got one shot)
BChE
pseudocholinesterase, non specific…, serum cholinesterase, prefers butyrylcholine as a substrate, generally distributed
reversible ACE inhibitors
physostigmine, neostigmine
irreversible ACE inhibitors
organic phosphates
electric fish
contain tissue rich in nicotinic receptors (packed with ACh receptors)
poisonous snakes
contain α toxins (peptides) that interact with cholinergic receptors in a way that causes irreversible antagonism
structure of the nicotinic receptor
5 subunits (α, α, β, δ, γ) in a circular array, the center is a gated ion channel
myastenia gravis is caused by
antibodies to ones own nicotinic receptors
nicotinic receptors require the binding of
TWO ACh molecules (causes positive ion influx), all or none switch
goal of nicotinic receptor activation
is depolarization
dual response
continuous or massive nicotinic receptor stimulation causes desensitization or a failure to repolarize (initial stimulation followed by cessation)
N(g) blocker
6, hexamethonium (ganglionic synapses and adrenal medulla)
N(m) blocker
10, decamethonium (neuromuscular junctions of somatic system)
methonium compounds
variation in chain length, block various nicotinic receptors with specificity
all nicotinic receptors require
two α subunits for ACh binding
ganglionic nicotinic receptor subunits
2α3, 3β4
muscarinic receptor structure
integral membrane proteins with a single membrane spanning polypeptide (seven times)
M2, M4
G(i) inhibition of cAMP, increased K+ currents
M1, M3, M4
G(q), increase in intracellular Ca2+
muscarinic receptor effect
slow, graded response, synapses less structured, Ach degredation is slwoer (used to regulate organ intrinsic activity)
muscarinic receptor blocker
atropine
utility of agents depends on
specificity of receptor subtype, availability (ability to penetrate to desired sites)
penetration to CNS
tertiary amines, hydrophobic compounds (un charged)
lots of Ach
causes the activation of nicotinic receptors (and therefore, sympathetic system as well)
lots of ACh and atropine
increase in autonomic ganglia firing rate and an increase in BP and heart rate
ACh as a drug
is not much use due to rapid degredation
methacholine
is resistant to hydrolysis, used opthalmologically, and has muscarinic and nicotinic effects
bethanechol
muscarinic agonist, resistant to degradation, pronounced in GI and UT smooth muscle, NO NICOTINIC EFFECTS
ACE inhibitor and bethanechol
additive effects
Methacholine and ACE inhibitor
synergistic effects
bethanecol administration
orally or subcutaneously, IV/IM negates specificity (toxic)
bethanecol structure and purpose
quarternary amine; used to treat urinary retention, GI stasis (post-op), diagnosis of anti-cholinergic intoxication (there are better agents), locally for the eye
contraindications for muscarinic agonists
asthma, hypothyroidism, coronary insufficiency, peptic ulcer, physical obstruction (bronchioconstriction, hypotension, gastric secretion)
muscarine
muscarinic agonist, quaternary amine, found in mushrooms
pilocarpine
muscarinic agonist, tertiary amine, rarely used systemically, potent diaphoretic
pilocarpine clinical uses
topical: treatment of acute glaucoma, xerostemia, CF sweat test, sjorgen’s syndrome
diagnostic sweat test for CF
pilocarpine
sjorgen’s syndrome
pilocarpine (or M3 agonist), autoimmune attack of endocrine glands
belladonna alkaloids
night shade, atropine, muscarinic antagonist, highly specific, competitive, tertiary amines
atropine
competitive inhibition, tertiary amines, half life 24 hours
synthetic muscarinic antagonists
Tropicamide, Tolterodine, Tiotropium
Tropicamide
short half life, eyes
Tolterodine
selectivity for receptors,
Tiotropium
quaternary amine, lungs
indications for specific atropine use
cholinesterase poisoning, AHA emergency care
M3 selective agents treat
incontinence in the elderly
treatment of stable COPD
long acting β-adrenergic agonists and muscarinic antagonists
treatment for anti-muscarinic intoxication
AChE inhibitor (physostigmine), diazapam for psychotic effects
symptoms of muscarinic antagonist poisioning
cutaenous vasodilation, anhidrosis, anhydrotic hyperthermia, nonreactive mydriasis, delirium, urinary retention
preanesthetic scopalamine is
better than atropine
cholinesterase inhibitors high doses
can cause stimulation through natural leakage of ACh
cholinesterase inhibitors are important for
Myasthenia Gravis, Alzheimer’s, opthalmology, atony, termination of competitive cholinergic blocking drugs
ACE inhibitors toxic
used for insecticides and in chemical warfare
hexamethonium
blocks reflex effects
reversible competitive ACE inhibitor example
Donepezil
Donepezil
tertiary amine, longer acting, competitive antagonist
carbamoylating agents are
ACE inhibitors and are reversed by slow hydrolysis (2-6 hour half life)
Physostigmine
carbamoylating agent, ACE inhibitor, tertiary amine, ordeal bean
Neostigmine
carbamoylating agent, ACE inhibitor, quaternary amine
irreversible ACE inhibitor
organic phosphates, turnover is fast than enzyme removal, SARIN :(
sites of action for ACE inhibitors
muscarinic post-ganglionic junctions, ganglionic nicotinic junctions, nicotinic NMJs, CNS muscarinic and nicotinic junctions
lipid soluble ACE inhibitors
physostigmine, donepezil, organic phosphates –> reach all sites for inhibitor
ACE inhibitor quarternary amine
nesostigmine
used for parkinson’s
atropine (muscarinic antagonist) - high doses lead to CNS problems
prevents motion sickness
scopolamine
rapid hydrolysis of the acetylated enzyme
restores the native enzyme
organic phosphates produce
phosphorylated enzymes
increased inhibition of ACE eventually causes
blockage of signal transduction
vagotomy
neostigmine is no long effective after this procedure
acute attacks of glaucoma are treated with
physostigmine (ACE inhibitor)
given for relief of abdominal distension
neostigmine
ACE inhibitor with good CNS penetrance
Donepezil (theoretically good for Alzhimer’s)
ACh increase effect on skeletal muscle
facilitation followed by paralysis
AChE inhibitor in myastenia gravis
too little = myastenia crisis, too much = cholinergic crisis
why is neostigmine good for myastenia gravis?
longer acting, carbomylating, quaternary amine
edrophonium test
you know why
other treatments for myastenia gravis
immunosuppression, plasma exchange, thymectomy (ACE inhibitors treat the symptoms, not the disease)
lipophilic agents
easily pass into the brain
lipophilic agent used for Alzhimer’s
Donepezil
effects can be local or general (ACE inhibitor poisoning)
dermal vs. pulmonary exposure
miosis
pupil pinpointing
diazapam
alleviates convulsions in ACE inhibitor poisoning
cholinesterase reactivator
pralidoxime, must be given before the phosphorylated enzyme ages! ONLY effective against phosphorylating enzyme
muscarinic antagonist
atropine
hexamethonium
selectively blocks ganglionic receptors
central effects of nicotine
sharpening of attention, development of dependence
nicotine stimulation of
nucleus accumbens and prefrontal cortex when activate release dopamine (reward perception)
why do plants make nicotine?
as a defense mechanism
nicotine poisoning
empty stomach via activated charcoal, DONT USE basic solution
varenicline
partial agonist for α4β2 nicotinic receptors
trimethaphan
quarternary sulfonium, inhibit nicotinic ganglionic receptors
sympathetically lead effects of nicotinic ganglion receptors
arterioles and veins are dominant tone, therefore blocking causes vasodilation
mydriasis
pupil dilation
nicotinic ganglionic blocker used for
hypertensive crisis, controlled hypotension, upper spinal cord injury hyperreflexia control
neuromuscular blocking agents
curare, methonium (2 quarternary amine dichotomy allows for activation of both receptors at one time) produce flaccid paralysis
competitive inhibition of NMJ
d-tubocurarine, vecuronium <– bulky, nonflexible,
depolarizing agents (NMJ blocking)
methonium compounds, succinylcholine <— long and slender molecular configuration
depolarizing agents block function in two phases
- persistent depolarization 2. receptor desensitization
depolarizing agent vs. competitive inhibitor sequence of paralysis
limbs/neck, diaphragm last; comp. small rapid muscles first, depolarization. small rapid muscles after neck
densensitization
postsynaptic membrane is repolarized but the nicotinic receptors do not respond to agonists, recovery is slow
during phase I there can be
significant loss of K+ from muscle
succinylcholine
characterized by fast action, depolarizing agent, rapidly hydrolyzed by butyryl cholinesterase
use of neuromuscular junction blockers
muscle relaxation as a surgical anesthesia adjunct, orthopedic procedures, intubation, electroshock therapy
neuromuscular blocking agent drug interactions
ACE inhibitors, inhalation anesthetics, certain antibiotics, calcium channel blockers
neuromuscular agent disease interactions
reduced cholinesterase, malignant hyperthermia, soft tissue damage (hyperkalemia), muscular disorders
reduced plasma cholinesterase and succinylcholine
prolonged apnea
overdose of NMJ blocker
prolonged apnea, CV collapse, histamine release