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Fundamentals of Pharmacology > L4: Drug Action at Receptors > Flashcards

L4: Drug Action at Receptors Flashcards

Learning Objectives: • Explain the role of receptors in cell signalling • Define the terms “specificity”, “affinity” and “efficacy” • List the main forms of antagonism produced by drugs • Describe the differences between the actions of full agonists, partial agonists and competitive antagonists on receptors - Describe the effect of a reversible competitive antagonist on the log concentration vs response curve for an agonist

1
Q

What are receptors?

A

Protein macromolecules that are inserted across lipid bilayer of cell

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2
Q

2 main functions of receptors

A

1) Recognition/detection of extracellular molecules
2) Transduction

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3
Q

What is transduction?

A

Detect the presence of an extracellular membrane, then bring changes in cell activity

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4
Q

How do receptors interact with/ bind to with certain chemicals?

A

High degree of specificity

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5
Q

How are receptors named/classified?

A

With respect to the drugs they bind

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6
Q

Name given to any chemicals that bind to receptors

A

Ligands

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7
Q

Equation of binding of drug (D) to receptor (R)

A

D + R ⇄ DR

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8
Q

Whats the shape of a plot of proportion of receptors occupied vs drug concentration?

A

Rectangular hyperbola

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9
Q

What is the plot of proportion of receptors occupied (p) vs log (D)?

A

Symmetrical sigmoid

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10
Q

Define affinity of a drug for its receptor (KD)

A

Molar concentration of drug required to occupy 50% of the receptors at equilibrium

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11
Q

How is the concentration of drug given as?

A

KD

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12
Q

Is the KD high or low if a drug has a high affinity?

A

LOW

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13
Q

Equation for rate of FORWARD reaction

A

k+1 (D)(R)

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14
Q

Equation for rate of BACKWARD rate

A

k-1 (D)(R)

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15
Q

What is KD a measure of?

A

A measure of how tightly the receptor holds onto the drug once they come together

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16
Q

What is the KD?

A

Equilibrium Dissociation Constant

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17
Q

What is an agonist?

A

Substance that binds & active the receptor, then produce a conformational change in the shape of the receptor to lead a response in a cell/tissue

18
Q

What is efficacy?

A

Ability of a drug to activate the receptor

19
Q

What is affinity?

A

Strength of drug binding with receptor

20
Q

What are the 2 types of agonist?

A

Full & Partial

21
Q

What is a full agonist?

A

High efficacy; effective at activating receptors

22
Q

What is the response of a full agonist?

A

Maximal response whilst activating a fraction of available receptors

23
Q

What is a partial agonist?

A

Low efficacy; less effective at activating receptors

24
Q

What is the response of a partial agonist?

A

Fail to produce full response despite occupying all available receptors

25
Q

How is the overall response of an agonist determined by?

A

Affinity & Efficacy

26
Q

What do we call drugs that show both affinity & efficacy at receptors?

A

Agonist

27
Q

Why is the EC50 for an agonist drug not always the same?

A

Determined by affinity & efficacy

28
Q

What is an antagonist?

A

A drug that stops the action or effect of another substance

29
Q

3 forms of antagonism

A

Chemical, Pharmacokinetic, Physiological

30
Q

What happens in chemical antagonism?

A

A drug combines with another to form an inactive product

31
Q

What happens in pharmacokinetic antagonism?

A

Decrease another drug’s concentration at the site of action

32
Q

What happens in physiological antagonism?

A

2 drugs act to produce opposing effects, so they cancel each other out

33
Q

Which forms of antagonists does not act at the receptor?

A

Chemical, Pharmacokinetic and Physiological

34
Q

Which forms of antagonists act at the receptor?

A

Competitive & Non-Competitive

35
Q

What are competitive antagonists?

A

Compete with agonist for the same site on the receptor molecule, but don’t activate it

36
Q

What are non-competitive antagonists?

A

Act at a different site on the receptor closely associated with it

37
Q

What are reversible competitive antagonists?

A

Used to inhibit the effects of a neurotransmitter/hormone

38
Q

How can reversible competitive antagonists inhibitory effects be overcome?

A

Increasing concentration of the AGONIST

39
Q

What happens to the graph for reversible competitive antagonists?

A

Parallel shift to the right of the AGONIST

40
Q

What are x & y axis on the reversible competitive antagonists graph?

A

x: log concentration of (agonist)
y: response

41
Q

What happens to the line in the presence of an antagonist?

A

Shifts to the right

42
Q

What happens to the shift in a IRREVERSIBLE competitive antagonist graph?

A

Shift is not parallel, inhibition they produce is not overcome by increasing agonist concentration

Fundamentals of Pharmacology (11 decks)

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