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Ther 201 2nd Exam > Cholinergic Receptors > Flashcards

Cholinergic Receptors Flashcards

1
Q

Ach Synthesis:
What are the substrates?
What is the enzyme?

A
  1. Choline and Acetyl CoA

2. Choline acetyltransferase

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2
Q

Ach Transmission:

Before synthesis, choline is first sequestered into the neuron by a ______ transport.

A

Carrier mediated transport,

specifically Na-Choline symport.

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3
Q

Ach Transmission:

What is the Rate Limiting Step of this transmission?

A

The entry of Choline into the neuron via Na-Choline symport

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4
Q

Ach Transmission:

After synthesis, Ach is packed into small vesicles via ______ transport

A

Carrier mediated transport.

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5
Q

Ach Transmission:

What triggers the fusion of the Ach-filled vesicles with the cell membrane for exocytosis?

A

Entry of Ca2+ ions into the neuron via Voltage-gated ion channels.

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6
Q

Ach Transmission:

Ach can now bind to 2 kinds of Cholinergic receptors. What are they? What are their characteristics

A
  1. Nicotinic -ligand gated ion channel, fast,

2. Muscarinic - GPCR, slow

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7
Q

Ach Transmission:

To end the signal transmission, Ach can now be degraded by what enzyme?

A

Acetylcholinesterase

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8
Q

Nicotinic vs. Muscarinic:
Where are they usually found?
How many receptor subtypes?

A

Nicotinic: found at Ganglia/CNS and Neuromuscular jxn; 2 subtypes (ganglionic and neuromuscular)

Muscarinic: found at <3, vascular endothelium, smooth muscles and EXOcrine glands; 5 subtypes (M1-M5)

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9
Q

What are the drugs/toxins that are responsible for blocking the Nicotinic receptors?

A
  1. Hexamethonium (blocks ganglionic nicotrinic receptor)

2. Tubocurarine and alpha-bungarotoxin (blocks neuromuscular nicotinic receptor)

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10
Q

Nicotinic receptors:
Ganglionic Nicotinic Receptors are usually found where?
How bout Neuromuscular Nicotinic Receptors?

A

Ganglionic N.R. usually found at Autonomic, and sensory ganglia, including CNS (basta nerves)

Neuromuscular N.R.usually found at Neuromuscular Junction.

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11
Q

What are the common agonists for Nicotinic receptors?

A

Both Ganglionic and Neuromuscular N.R. respond to Acetylcholine and Carbamylcholine (also called Carbachol).

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12
Q

Bungarotoxin blocks the Neuromuscular N.R.

There are 2 types of bungarotoxin. What are they? How are they different?

A

Alpha-Bungarotoxin: blocks POSTsynaptic N.R.
Beta-Bungarotoxin: blocks Neurotransmitter release at the PREsynaptic cell membrane by preventing fusion of the vesicle w/ the cell membrane

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13
Q

Muscarinic Receptors:

There are 5 types of Muscarinic Receptors (M.R.). Where are they usually found?

A

M1: NERVES
M2: HEART, nerves, smooth muscles
M3: EXOcrine GLANDS
M4 and M5: CNS

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14
Q

Muscarinic Receptors:

What are the Mechanisms of these subtypes?

A

M1, M3, M5: promote IP3 and DAG cascade (Gq, phospholipase C)

M2 and M4: ihibits cAMP production (Gs, adenylyl cyclase)

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15
Q

What are Cholinomimetic Drugs?

Types? Divisions?

A

They are drugs that has the same action with Ach. AGONISTIC.

They are divided into 2: Direct and Indirect-Acting drugs.

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16
Q

Are there any subtypes of Direct acting drugs?

A

Yes. Direct-Acting drugs are further divided into 2: those acting on Muscarinic and those acting on Nicotinic receptors.

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17
Q

Direct-Acting Muscarinic Cholinomimetic Drugs:

There are two main examples of this - CHOLINE ESTERS and ALKALOIDS. What are the characteristics of these two?

A

Choline Esters:
- lipid insoluble, presence of BETA-METHYL group prevents its hydrolysis in GIT hence not given orally.

Alkaloids:
- easily absorbed at site of admin., excreted in the kidneys, of plant origin,

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18
Q

Direct-Acting Muscarinic Cholinomimetic Drugs:

Give an example of a choline ester and an alkaloid.

A
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19
Q

Direct Acting Cholinomimetic Drugs:
Is this for Nicotinic, Muscarinic or both receptors?
1. Acetylcholine & Carbamylcholine/Carbachol
2. Bethanechol & Pilocarpine
3. Nicotine & Varenicline

A
  1. Both
  2. Muscarinic
  3. Nicotinic
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20
Q

Direct Acting Cholinomimetic Drugs:

When is Bethanecol used?

A

used for spastic bladders/atony

Promotes MICTURITION

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21
Q

Direct Acting Cholinomimetic Drugs:

Patient has GLAUCOMA. What drug will you give?

A

Pilocarpine

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22
Q

Direct Acting Cholinomimetic Drugs:

A PARTIAL agonist of N.R. which comes in the form of Nicotine patches.

A

Varenicline

Used in patients to reduce their longing for nicotine.

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23
Q

What are the effects of the Direct-Acting Cholinergic Agents to the body?

A

May technique dito HAHAHA:
Generally, almost all will constrict in response to cholinomimetic agents EXCEPT for Arteries, Veins and Sphincters (first 2 will dilate at low dose but constrict at high dose). Glands will be stimulated.

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24
Q

What are the effects of the Direct-Acting Cholinergic Agents to the Heart?

A

@ the heart, these drugs will affect SA node (dec <3 rate), Atrium and Ventricle (dec contractile strength) and AV node (dec conduction velocity)

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25
Q

What do these terms mean?
Negative Chronotropy?
Negative Inotropy?
Negative Dromotropy?

A

All of these are the effects of cholinergic agents in the heart.
(-) Chronotropy = dec <3 rate
(-) Inotropy = dec contractile strength
(-) Dromotropy = dec conduction velocity

26
Q

CNS contains BOTH muscarinic and nicotinic receptors. Brain has more ____ receptors and Spinal cord has more ____ receptors.

A
  1. Muscarinic
  2. Nicotinic
    * *@ low doses = mild alerting effects
    * *@ larger doses = tremors, emesis, etc
27
Q

Peripherally Acting Cholinesterase (acts on PNS):
Their site of action is in the degradation of Ach which will enhance cholinergic transmission.
Give 2 examples of cholinesterase.

A
  1. Acetylcholinesterase - found primarily IN THE BLOOD and RBC membranes, NMJs and neural synapses
  2. Buterylcholinesterase - produced in liver, found IN THE PLASMA
28
Q

Indirect Acting Cholinomimetic Drugs:
Anticholinesterases are considered cholinomimetic since they enhance Ach effect. Anticholinesterases are divided into 3 groups, what are they?

A
  1. Short acting Anti-ACHesterases (drug Edrophonium)
  2. Medium acting Anti-ACHesterases (drugs Neostigmine, Pyridostigmine, Physostigmine)
  3. Long acting/Irreversible Anti-ACHesterases (Organophosphates)
29
Q

Characteristics of Indirect Acting drugs:

What are some of the characteristics of Edrophonium (short-acting Anti-Achesterase)

A
  • a quarternary alcohol
  • binds reversibly, very weak ionic bond with ACHesterases
  • used in Myasthenia Gravis diagnosis
30
Q

How is Edrophonium used in Myasthenia Gravis diagnosis?

A

Edrophonium is short acting (10mins). Giving this drug to patient w/ MG will enable him to raise his arms for more than 2 mins and his ptosis will disappear. If this effects are seen and expires after ~10 mins, then a diagnosis of MG is made.

31
Q

What are some of the characteristics of Neostigmine, and other -stigmines (medium-acting Anti-Achesterase)?

A
  • a carbamic acid ester of alcohol
  • forms cabomylated covalent bond with enzyme
  • persists for hours, maintenance drug for MG.
32
Q

What are some of the characteristics of Organophosphates (Irreversible Anti-Achesterase)?

A
  • forms a phosphorylated covalent bond w/ enzyme
  • the longer they bond, the stronger they become (parang may “ageing” effect)
  • inactivates ACHesterases, need to produce new ones
  • can cause severe type of Peripheral Nerve Demyelination
33
Q

2 Important Signs of Organophosphate toxicity!!!

A
  1. Salivation

2. Seizures

34
Q

What is Pralidoxime?

A
  • an ACHesterase regenerator; antidote to organophosphate poisoning
  • most effective before the “ageing effect” of the phosphorylated covalent bond starts
35
Q

What is Malathion?

A

An parasympathomimetic organophosphate that binds irreversible to cholinesterase

36
Q

Symptoms of Toxicity for Indirect Acting Cholinomimetic Agents:
Hint: DUMBELS

A

DUMBELS:

Diarrhea, Urination, Myosis, Bronchoconstriction, Excitation, Lacrimation, Salivation

37
Q

Centrally Acting Cholinesterase Inhibitors:
What are their characteristics?
Used in what conditions?
Give examples.

A
  • orally active, lipid soluble, enter CNS
  • used in the symptomatic treatment of Alzheimer’s and dementia
  • ex. Rivastigmine, Galantamine, Donepezil
38
Q

Ganglion Stimulants are agonists or the ganglionic N.R.
Effects?
Give an example

A
  • generalized stimulation of autonomic ganglia (tachycardia, inc BP, Inc in secretions)
  • Dimethylphenylpiperazinium (DMPP):
39
Q

Cholinoceptor Blockers:

Enumerate the 4 MOAs for cholinoceptor blockers.

A
  1. Inhibit choline uptake/intake
  2. Inhibit Ach release
  3. Block Postsynaptic receptors
  4. Persistent postsynaptoc depolarization
40
Q

An example of a Cholinoceptor blocker are muscarinic antagonists. Describe them.

A

Main examples: Atropine and Scopolamine
Chemistry of muscarinic antagonists:
1. natural alkaloids (atropine and scopolamine) - GIT absorbable
2. tertiary ammonium - GIT absorbable
3. quarternary ammonium - poor GIT absorption

41
Q

Why do some antihistamine and antidepressant drugs have antimuscarinic effects?

A

Because their structures are similar to the tertiary ammonium that are muscarinic blockers

42
Q

Atropine Toxicity symptoms?

A

Blind as a bat (cycloplegia/ near vision)
Dry as a bone (decreased sweating)
Red as a beet (thermoreg, blood vessels in skin dilate due to decreaseed sweating)
Mad as a hatter (hallucinations)
Hot as hell (thermoreg. fever becaus you dont perspire)

43
Q

Presynaptic Cholinergic Inhibitor
Give MOA and site of Drug action.
Hemicholinium

A

Block transport of Choline into neuron for Ach synthesis;

Reuptake;

44
Q

Presynaptic Cholinergic Inhibitor
Give MOA and site of Drug action.
Triethylcholine

A

Mimics choline, blocks transport of choline;

Synthesis;

45
Q

Presynaptic Cholinergic Inhibitor
Give MOA and site of Drug action.
Vesamicol

A

Blocks Ach transport into vesicles;

Storage

46
Q

Presynaptic Cholinergic Inhibitor
Give MOA and site of Drug action.
Botulinum toxin

A

Inhibit Ach release by blocking Ca2+ needed to release the vesicles.
Release

***active component is peptidase. causes parasympathetic and motor paralysis

47
Q

Presynaptic Cholinergic Inhibitor
Give MOA and site of Drug action.
Apha and Beta-bungarotoxin

A

For Alpha: blocks post synaptic Ach receptors; Receptor of transmitter

For Beta: prevent fusion of vesicles with cell membrane; Release

48
Q

Presynaptic Cholinergic Inhibitor
Give MOA and site of Drug action.
Aminoglycoside antibiotics

A

Blocks release of Ach.

CONTRAINDICATED in patients with M.G.

49
Q

Drugs Affecting Autonomic Ganglia
Give MOA and site of Drug action.
Magnesium Ion

A

Competes with Ca2+;

Release

50
Q

Drugs Affecting Autonomic Ganglia
Give MOA and site of Drug action.
Nicotine

A

Prolong depolarization

Receptor

51
Q

Drugs Affecting Autonomic Ganglia
Give MOA and site of Drug action.
Hexamethonium, Trimetaphan, Tubocurarine

A

interference with postsynaptic action of Ach, blocked of nicotinic receptor

52
Q

Ganglion blocking drugs block ALL AUTONOMIC and ENTERIC GANGLIA.
What are its clinical manifestations?

A 
Mnemonic: HILIG
Hypotension
Inhibition of secretions
Loss of cariovascular reflexes
Impaired micturition
Gastrointestinal paralysis
53
Q

Neuromuscular blocking drugs:

What are the 2 ways of blocking neuromuscular transmission?

A
  1. Presynaptically - inhibit Ach synthesis

2. Postsynaptically - acto on receptor or ion channel

54
Q

Neuromuscular blocking drugs:

What are its uses?

A
  1. Used in surgery, decreases the dose for anesthesia required
  2. For intubation (paralyze and sedate)
  3. muscle spasm control
  4. for STATUS EPILEPTICUS
55
Q

What is status epilepticus?

A

uncontrolled and prolonged seizures of the respiratory muscles leading to zero breathing and hypoxia

56
Q

Two types of Neuromuscular blocking drugs?

A
  1. Non depolarizing drugs

2. Depolarizing drugs

57
Q

Non depolarizing drugs:

MOA? Effects?

A
  • competitive antagonists,
  • blocks the pore of the ion channel
  • may also block prejunctional Na channels
  • motor paralysis, consciousness and awareness of pain were normal
58
Q

Non depolarizing drugs:

What is the sequence of motor paralysis?

A
  1. extrinsic eye muscles
  2. facial muscles
  3. limbs and pharynx
  4. respiratory muscles
59
Q 
Non depolarizing drugs:
Drugs are always accompanied by unwanted effects. What are the unwanted effects of the ff:
1. Tubocurarine
2. Vecuronium
3. Gallamine/Pancuronium
A
  1. fall in BP due to ganglion block
  2. less ganglion block and release of histamine
  3. block muscarinic receptors in the <3
60
Q

Depolarizing Drugs:
The MOA of these drugs has 2 phases Phase 1 (or depolarization block) and Phase II (desensitized). Give the characteristics of each phase.

A
  1. Phase 1: maintained depolarization at the endplate, loss of excitability, FASCICULATIONS,

Ther 201 2nd Exam (6 decks)

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