Session 8

Question 0

What is affinity?

Answer 0

Ability to bind to the receptor

Question 1

How do you calculate molarity?

Answer 1

g/L/molecular weight

Question 2

Define efficacy

Answer 2

How good a compound is at responding (efficacy is the maximum effect that a drug can produce).
It includes the intrinsic efficacy and the cell/tissue dependent factors

Question 3

What is drug action governed by?

Answer 3

Affinity and intrinsic efficacy

Question 4

Describe agonists and antagonists in terms of affinity and intrinsic efficacy

Answer 4

Agonists - have both affinity and intrinsic efficacy

Antagonists - have only affinity

Question 5

How can drug-receptor interactions when binding be measured?

Answer 5

Binding of a radioligand to cells or membranes are prepared from cells. Low [ligand] = low binding
High [ligand] = high binding

Question 6

What is the B max?

What information can we glean from this value?

Answer 6

B max is the binding capacity of the compound. Tells us about the receptor number.

Question 7

What is Kd?

Answer 7

The dissociation constant –> a lower Kd means higher affinity
Concentration needed to occupy 50% of receptors

Question 8

Define concentration and dose

Answer 8

Concentration = conc of drug as site of action e.g. in cells/tissues
Dose = conc of drug at site of action unknown e.g. to patient in mg or mg/kg

Question 9

What is EC50?

Answer 9

The effective concentration giving 50% of the maximal response. It’s a measure of agonist potency and depends on both intrinsic efficacy and affinity.

Question 10

Define selectivity

Answer 10

The tendency of the drug to have effects other than it’s intended effect.

Question 11

What is IC50?

Answer 11

Inhibitory concentration that gives 50% of the maximum inhibition

Question 12

What is the use of a receptor reserve?

Answer 12

It makes the cell/tissue more sensitive to the stimulant, allowing for a response at smaller concentrations

Question 13

What does changing the number of receptors on a cell do?

Answer 13

Alters the potency

Question 14

What is a partial agonist?

Answer 14

A compound that does not produce a maximal response even if all the receptors are being used.
The EC50 of a partial agonist = it’s Kd

Question 15

Give an example of partial agonists

Answer 15

Opiods - used for pain relief/recreationally but can lead to respiratory depression (bit not good)

Question 16

Can partial agonists become agonists?

Answer 16

Yes. If there is an increase in the number of receptors then although there is low efficacy there will be sufficient bindings to ensure a full response

Question 17

What does maximal response indicate?

Answer 17

Intrinsic activity

Question 18

What are reversible competitive antagonists?

Answer 18

Reversible competitive antagonism (commonest and most important in therapeutics) - depends on dynamic equilibrium between ligands and receptors. The inhibition is surmountable (overcome) by addition of more agonist.

Question 19

What is irreversible competitive antagonism?

Answer 19

Irreversible competitive antagonism – occurs when the antagonist dissociates very slowly or not at all (e.g. because of a covalent bond between ligand and receptor). The inhibition is non- surmountable.

Question 20

What is non-competitive antagonism?

Answer 20

Non-competitive antagonism - generally a post-receptor or allosteric event.

Question 21

What effect does a reversible competitive antagonist have on an agonist concentration-response curve?

Answer 21

Reversible competitive antagonists cause a parallel shift to the right of the agonist concentration-response curve

Question 22

What effect does an irreversible competitive antagonist have on an agonist concentration-response curve?

Answer 22

Irreversible competitive antagonists cause a parallel shift to the right of the agonist concentration-response curve (at higher concentrations suppress the maximal response).

Question 23

Define potency

Answer 23

Potency is the amount of a drug needed for it to have the maximum effect. This is a combination of both affinity and efficacy

Question 24

What is homologous desensitisation?

Answer 24

Homologous desensitisation – the process by which only the signal from the stimulated receptor is reduced.

Question 25

What is heterologous desensitisation?

Answer 25

Heterologous desensitisation – the process when receptors for other agonists become less effective even when only one has been continuously stimulated.