Receptor Theory

Question 1

Define efficacy

Answer 1

The likelihood of activation of a receptor and stimulation of cellular response.
This is dependent on intrinsic efficacy and cell dependent factors.

Question 2

Since intrinsic efficacy

Answer 2

The ability of a ligand to activate a receptor

Question 3

What is Kd? Measure of?

Answer 3

Kd is the dissociation constant.
Concentration of ligand at which half of all of the available receptors are bound.
Measure of affinity.
Lower Kd = greater affinity

Question 4

What is EC50?

Answer 4

The effective concentration of drug required to give 50% of the maximum response.
It is a measure of potency.
Lower EC50 = greater potency

Question 5

Define potency.

Answer 5

A measure of the amount drug required to produce an effect of give magnitude.

Question 6

What is Athsma

Answer 6

Reversible airflow obstruction caused by bronchoconstriction

Question 7

What are two drugs used to treat asthma

Answer 7

Salbutamol salmeterol

Beta2 agonists

Question 8

How does salbutamol target beta 2

Answer 8

Kd low for beta 2, high for beta1
Route of administration - oral spray
Beta 2 selective efficacy

Question 9

How does salmeterol target beta2

Answer 9

Much higher affinity for beta 2 than 1

Question 10

What do spare receptors result in? EC50 and Kd

Answer 10

Less that 100% receptor occupancy results in 100% response

EC50

Question 11

What is the relationship between receptor occupancy and response

Answer 11

Transduction system and amplification by second messenger
The level if endogenous agonist
Number of receptors
Properties of the tissue

Question 12

What is the consequence of having more receptors than requires

Answer 12

Increased sensitivity, allowing for response at low agonist concentration.

Question 13

How does number of spare receptors affect potency?

Answer 13

Increasing number of receptors increases potency.

EC50 gets

Question 14

How does the plot of dose response look for a partial agonist.

Answer 14

Plateaus at a lower Emax than full agonist

May have higher potency.

Question 15

Describe a clinical use for a partial agonist.

Answer 15

Opiod receptor partial agonists allow adequate pain control with less respiratory depression and allow withdrawal from full agonist morphine.

Question 16

Give 3 types of antagonist

Answer 16

Reversible competitive
Irreversible competitive
Non competitive

Question 17

How does the presence of an reversible competitive antagonist shit the dose response cure?

Answer 17

Shift to the right.

Still reaches Emax eventually

Question 18

Describe how irreversible competitive antagonist shifts the dose response curve.

Answer 18

Shifts to the right
Can reach Emax at low antagonist concentration
Reaches a lower Emax at higher antagonist concentrations as spare receptors are filled.

Question 19

Describe the changes in the presence of a non competitive antagonist.

Answer 19

Binds to allosteric site.
Shifts dose response curve to the right.
Lowers Emax
Similar to irreversible, differentiated by tests

Question 20

Describe except or desensitisation

Answer 20

Repeated stimulation may lead to changes in responsiveness.
Prevent damage from excess stimulation
May occur in response to phosphorylation
May occur in response to reversible internalisation.

Question 21

Describe homologous desensitisation

Answer 21

Repeated stimulation of single receptor population reduced the response from that receptor population

Question 22

Describe heterologous desensitisation

Answer 22

Occurs when a single receptor has been continuously stimulated resulting in responses from other agonists becoming blunted.

Question 23

Define affinity

Answer 23

The degree to which a ligand binds to its receptor