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SL12100 Health and Disease Y1 > Lecture 19 - Receptor antagonist and modulators > Flashcards

Lecture 19 - Receptor antagonist and modulators Flashcards

1
Q

Antagonist

A

A ligand that binds but does not activate a receptor

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2
Q

Example of an antagonist

A

atropine

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3
Q

Competitive antagonist =

A

compete with agonists for the same receptor binding site

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4
Q

A competitive antagonist may be ………………. or ……………….

A

reversible
irreversible

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5
Q

What is a reversible competitive antagonist?

A

The antagonist can outcompete the agonist and reduce the agonist response. BUT increasing agonist concentration will eventually outcompete the agonist

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6
Q

Draw a concentration response curve for reversible competitive antagonist. Label the axis. Show agonist A, Agonist A with 100nM of antagonist AND Agonist A with 800nM antagonist.

A
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7
Q

Describe this concentration response curve for reversible competitive antagonism.

A

In the presence of an antagonist, a higher concentration of Agonist A is needed to produce the same response. The curve is shifted along the X axis

The Emax stays the same for agonist A when the concentration of antagonist increases BUT the EC50 of agonist A gets larger- higher concentration of agonist A is required to produce the same response.

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8
Q

Irreversible competitive antagonism=

A

the antagonist permanently binds to receptor so no amount of agonist can dislodge it. The response of the agonist is reduced.

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9
Q

Draw a concentration response curve for irreversible competitive antagonist. Label axis. Include agonist A, agonist A with 100nM of antagonist and agonist A with 800nM of antagonist.

A
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10
Q

Describe this concentration response curve for irreversible competitive antagonist.

A
  • In the presence of the antagonist, a higher concentration of Agonist A cannot dislodge the antagonist from the receptors. There is reduced response.
  • When concentration of antagonist increases, Emax of the agonist A decreases and EC50 increases (more agonist needed to produce response)
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11
Q

We can quantify antagonism using…

A

Schild plot and pA2

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12
Q

What is a schild plot used for?

A

a way to determine the nature and potency of an antagonist.

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13
Q

the y axis of a schild plot=

A

the log concentration of the antagonist (M)

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14
Q

the x axis of a schild plot =

A

log(dose ratio -1)

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15
Q

draw an example schild plot

A
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16
Q

What is the equation for dose ratio?

A
17
Q

In a schild plot, where is the pA2 value?

A

the x intercept

18
Q

What is pA2 used to measure?

A

the potency of the antagonist

19
Q

A higher pA2 value =

A

more potent antagonist.

20
Q

If two antagonists have the same pA2 value, what does this mean?

A

suggests that they act on the same receptor

21
Q

What is the equation for pA2?

A

pA2=
log⁡(dose ratio-1) -log[antagonist]

22
Q

Draw the schild plot for competitive and non-competitive antagonism

A
23
Q

What is a response determined by?

A

affinity- how well a drug binds to receptor and efficacy- how well a drug activates a receptor.

24
Q

Agonists and competitive antagonists will bind at the same site on the receptor. What is this site called?

A

orthosteric site

25
Q

Other drugs/molecules can bind onto other sites on the receptor and modify the effects of the agonist. What are these molecules called? What is the name of their binding site?

A
  • allosteric modulators
  • bind to the allosteric site
26
Q

Name and explain the two types of modulation

A
  1. Affinity modulation: the affinity allosteric modulator will affects how well the agonist binds to the orthosteric site
  2. Efficacy modulation: efficacy allosteric modulators affects how the agonist activates the receptor
27
Q

What is allosteric agonism?

A

allosteric modulators bind to the allosteric site and will push the receptor into an active conformation to produce a response.

28
Q

How does an affinity allosteric modulator effect the concentration response curve?

A

Affinity allosteric modulators alter how well the agonist binds to the receptor. Therefore, more/less of agonist is required for same response. The concentration response curve is therefore shifted to the left/right (EC50 changes)

29
Q

Draw the concentration response curves for positive affinity modulation and negative affinity modulation

A
30
Q

Describe how efficacy allosteric modulators effect the concentration response curve.

A

Efficacy allosteric modulators alter how well the agonist activates the receptor. The full response caused by the agonist is raised or supressed. The concentration response curve is shifted upwards or down- the Emax is raised or lowered.

31
Q

Draw the concentration response curves for both positive and negative efficacy modulation

A
32
Q

Another name for negative efficacy modulation…

A

non-competitive antagonism

SL12100 Health and Disease Y1 (18 decks)

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