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Drugs: From molecule to man > ELM5: Agonists to antagonists > Flashcards

ELM5: Agonists to antagonists Flashcards

1
Q

How does an agonist work?

A
  1. Agonist introduced
  2. Changes in equilibrium and receptor favours an active state
  3. Binding energy from interaction stabilises active state
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2
Q

What is a functional assay used for ?

A

To measure what happens when a drug binds

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3
Q

What are the 4 different types of functional assasy?

A

Cell based biochemical assay
Organ bath assay
Electrophysiology
Whole organism assay

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4
Q

What is a cell based biochemical assay?

A

Cells grown in lab in plates
Often used for GPCRs

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5
Q

What is an organ bath assay?

A

Organ removed from animal and put in tissue bath and supplied with nutrients and oxygen
Measure how normal functions change in response to drugs

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6
Q

What is electrophysiology?

A

Measures how membrane potential of cell changes with drugs
Uses electrodes on or in cell
Measure channel activity

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7
Q

What is a whole organism assay?

A

Measure changes in behaviour or disease state caused by drugs
See drug in action and factors like absorption and metabolism

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8
Q

What is the concentration-effect?

A

Using results of assays to plot a group showing relationship between agonist concentration and its effect

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9
Q

What shape is the plot for a concentration effect?

A

S shaped or sigmoid

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10
Q

What is EC50?

A

Measure of potency

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11
Q

What is potency?

A

Concentration or dose of drug needed to produce a specified effect

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12
Q

What is the specified effect in EC50?

A

50% of Emax for the drug

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13
Q

What is the difference in the measurements used for binding and functional assays?

A

Binding is KD and Bmax
Functional is EC50 and Emax

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14
Q

What is the difference between potency and affinity?

A

EC50 is potency and KD is affinity

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15
Q

How can spare receptors change the relationship between Bmax and KD?

A

Some receptors aren’t activated
Maximum affect isn’t reached
Emax isn’t directly related to Bmax
Emax reached before Bmax

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16
Q

How can spare receptors activating multiple proteins change the relationship between KD and Bmax

A

One receptor activates multiple proteins
Maximum effect isn’t always maximum binding as can be reached with only a few receptors
Emax reached before Bmax

17
Q

What do the values of EC50 and Emax depend on ?

A

Ratio of receptors to G protein
Number of G proteins a receptor activates

18
Q

How can EC50 be used to compare drug potency?

A

Small EC50 means high potency

19
Q

How can we compare selectivity using EC50?

A

See EC50 value at one receptor compared to another

20
Q

What is meant by efficacy?

A

How well a drug activates a receptor once its bound

21
Q

What are competitive antagonists?

A

Compete with agonists for receptor binding site
Remain in the site once bound

22
Q

What is the functional gaddum equation?

A

Same form used to describe competitive binding but used for antagonists and uses E Emax and EC50

23
Q

What are the predictions of the functional gaddum equation?

A

The maximal effect of the agonist is not changed
If antagonist is there you need more agonist to cause an effect

24
Q

What are reversible competitive agonists?

A

Eventually leave site

25
Q

What are irreversible competitive antagonists?

A

Stay in the site

26
Q

What are the characteristics of a competitive agonist in the presence of an antagonist compared to a control?

A

No change in maximum response
Increase in agonist EC50
Parallel shift of the curve to the right

27
Q

What is reversible competitive antagonism?

A

Antagonist binds reversibly to same site as agonist
Overcome by increasing agonist concentration

28
Q

What is non-competitive antagonism?

A

Antagonist and agonist bind at same time to different site
Conformational change means agonist can’t activate receptor
Not overcome by agonist increase

29
Q

What are some factors that may affect target site concentration in whole organism assays?

A

Absorption
Distribution
Excretion

30
Q

What is used for EC50 in dose-effect relationships?

A

ED50

31
Q

What is relationship between ED50 and potency?

A

Smaller ED50 means higher potency

Drugs: From molecule to man (21 decks)

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