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Pharmacology & Physiology 1 > Drug-Receptor Interactions > Flashcards

Drug-Receptor Interactions Flashcards

1
Q

What is the importance of receptors?

A
  • Pharmaceutical industry and drug development
  • Physiology of endogenous transmitters
  • chemical toxicity
  • Viral toxicity
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2
Q

How do agonists bind to their receptors?

A

Mostly reversibly, agonists bind to receptors and then dissociate

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3
Q

What are the 2 major types of receptors involved in drug interactions?

A
  1. Ligand Gated Ion Channels LIGC (ionotropic)

2. G-Protein Coupled Receptors GPCR (metabotropic)

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4
Q

Name an irreversible antagonist

A

Aspirin - acetylates COX enzyme

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5
Q

What is the role of the thalamus in the brain?

A

Thalamus modulates pain

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6
Q

How does receptor transduction occur via LIGC?

A

An influx of ions causes hyper/depolarisation causing a cellular effect

  • occurs in milliseconds
    e. g. nAChR
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7
Q

What is drug efficacy determined by ?

A
  • Threshold concentration
  • EC₅₀
  • maximal concentration
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8
Q

What is irreversible antagonism?

A

When an antagonist binds irreversibly either to agonist/non-agonist binding sites on the receptor
via covalent bonds
Reduces the number of free receptors

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9
Q

Why is the agonist-receptor binding weak?

A

Relatively weak and reversible binding due to Hydrogen and Ionic bonding
Van der waals forces allow dissociation

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10
Q

How do receptors limit the need for a large [drug]?

A

Receptors amplify signals so only a small number of drug-receptor interactions can produce a biological response

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11
Q

Where can partial agonists be found?

A

Present at receptors with high affinity but less efficacy

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12
Q

Using the agonist-receptor mechanism explain why opioids are so addictive to humans?

A

Thalamus in the brain contains many opioid receptors

There is therefore high opioid binding

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13
Q

Outline a drug receptor mechanism

A 
Drug A (agonist) + Receptor  AR  AR+ --> response 
                             (Ka occupation)(EC₅₀ activation)

Ka occupation governed by affinity
EC₅₀ activation governed by efficacy
- an agonist has both efficacy and affinity

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14
Q

What does a smaller Ka value mean?

A

Agonist has a greater affinity for receptors so binds more

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15
Q

Give an example of non competitive antagonism

A

Ketamine blocks glutamine receptors by acting at a different (allosteric) site in the receptor to glutamate (agonist)

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16
Q

How do G protein coupled receptors cause transduction?

A

An excitability change occurs, caused by ions or a secondary messengers causing cellular effects
via Ca2+ release or protein phosphorylation
- takes longer (seconds)
e.g. Muscarinic AcHR

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17
Q

What is the relationship between EC₅₀ and Ka for a maximum biological response?

A

Affinity (Ka) and Efficacy (EC₅₀) are not equal

- full occupancy isn’t required for a maximum response

18
Q

What is an Agonist?

A

A drug that binds to a receptor causing a biological response

19
Q

What is non competitive antagonism?

A

When the antagonist binds to a differing site from the agonist

20
Q

What is the law of mass action?

A

A + Rfree AR

A = [agonist]
Rfree = [free receptors]
AR = [agonist-receptor complexes]
21
Q

How does a non surmountable graph look?

A

Curve slope is reduced and the maximum is depressed

22
Q

How is drug affinity regulated?

A

Reversible binding of an agonist to its receptor is governed by the law of mass action

23
Q

What is the effect of partial agonists?

A

Reduce withdrawal effects

Reduce additive ‘highs’

24
Q

What is Bmax value?

A

Maximum number of receptors which can be bound by the drug

25
Q

What does the term drug affinity mean?

A

The ability of a drug molecule to bind to a receptor site

26
Q

What is meant by the term surmountable antagonism?

A

When the same maximal response is obtained via increasing [A] as you can out-compete the antagonist

27
Q

What is the threshold?

A

Maximum amount of drug required for a biological response?

28
Q

What is the relationship between Ant. and concentration curve?

A

In the presence of Ant., the concentration curve shifts to right as its linearly related

29
Q

What is Drug Efficacy?

A

The ability of a drug to elicit a biological response from a drug-receptor interaction

30
Q

What is the consequence of competitive antagonism?

A

If Kant < Ka, then Ant has a greater affinity for receptors than A
[A] must increase to overcome Ant binding to receptors

31
Q

What is EC₅₀?

A

The effective concentration giving a 50% biological response

32
Q

Explain what is meant by a partial agonist

A

An agonist drug producing a biological effect that is always less than the maximum capacity of the tissue

33
Q

Give an example of a partial agonist used for opioid addiction

A

Brupernorphine used for opioid addiction
- heroin induced highs are reduced in the presence of
partial agonists

34
Q

What is the law of mass action affected by?

A

Dependent on [reactants] (agonist and free receptor concentrations)

35
Q

Why is there a maximum no. of AR complexes that can form?

A

There is a maximal no. of AR interactions due to a finite number of receptors

36
Q

How does competitive antagonism arise?

A

A and Ant compete for the same receptor binding site

Reaction is then dependent on 2 equilibrium constants (Ka and Kant)

37
Q

What is Ka?

A

The amount of drug required to occupy 1/2 max no. of receptors
the [A] at equilibrium

e.g. Ka at 50nM means at this conc. 1/2 the max no. of receptors are bound by the drug

38
Q

What is the Ka value for drugs?

A

Each drug has its own individual Ka value

39
Q

Which drug molecules do receptors bind to?

A

Reversibly bind to both Agonists or antagonists only

40
Q

How is EC₅₀ used?

A

Used to compare drug potency (determined by drug efficacy and affinity)

41
Q

What is an Antagonist?

A

A drug blocking the effect of an agonist commonly by binding to its receptor antagonist binding to receptor inhibits biological responses

42
Q

What does the law of mass action predict?

A

Low [A] means lots of free receptors so few AR interactions

If [A] increases, more AR complexes form, reaction driven to right, so more [A], few receptors left
free => reaction reaches maximum

Pharmacology & Physiology 1 (9 decks)

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