L7 - Receptor Theory - Agonist and Anatagonists

Question 1

Contraction of ileum tissue in the presence of ACh method

Answer 1

ACh binds to receptor sets off a chain of events

• Activation of G proteins
• Second messenger systems
• Rise in intracellular Ca
• Activation of contractile machinery
• Contraction

Efficacy of agonist may influence the size of the response

Question 2

Concentration effect curves

Answer 2

Response = max.[Xa]n
([Xa]n + [EC50]n)

Max = maximum response (amplitude of contraction)
n = slope factor

Question 3

Concentration effect curves can be used to calculate?

Answer 3

EC50

Question 4

What is EC50 a measure of?

Answer 4

Agonist potency
Concentration giving 50% maximal response
The EC50 of an agonist for a receptor will vary between tissues, the affinity will not

Question 5

Potency depends on?

Answer 5

Affinity
Efficacy
Spare receptors

Question 6

The line that lies most to the left on the graph is the most/least potent?

Answer 6

Most potent

Question 7

If EC50 is shifted to the left compared to Kd

Answer 7

Receptor reserve – not 100% of receptors occupied to give maximal response – amplification of signal
Therefore, probability of agonist binding to receptor is high

Question 8

What is efficacy?

Answer 8

Is a measure of a single agonist-receptor complex ability to generate a response

Question 9

Agonists with different efficacies will produce?

Answer 9

Different maximal responses

Can still have the same EC50 value

Question 10

Agonist with 100% response has an efficacy value of?

Answer 10

1 = full agonist

Question 11

3 properties determine the effect of a drug in a living system

Answer 11

Specificity - interaction with a structurally defined receptor
Affinity - ability to bind to a receptor
- KD
Efficacy - ability to activate a receptor
- Full agonist = 1
- Antagonist = 0