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PHAY0003 > Receptors > Flashcards

Receptors Flashcards

1
Q

What are receptors?

A

Highly specialised proteins embedded in cell membranes that possess structurally defined binding sites

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2
Q

What is a drug receptor?

A

A macromolecule that a drug or molecule binds to cause a response

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3
Q

What are the 5 pieces of evidence for the existence of receptors?

A 
Potency
Unique actions
Specificity
Antagonism
Cloned receptors work the same as native receptors
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4
Q

What does high potency mean?

A

Only small quantities are required to produce a response

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5
Q

What are the 4 main classes of receptors?

A

Ligand-gated ion channels
Ionotropic receptors
Metabotropic receptors
Enzyme-linked and intracellular receptors

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6
Q

Which type of receptors produce the fastest response?

A

Ionotropic receptors (milliseconds)

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7
Q

What happens when a drug binds to ionotropic receptors?

A

The ion channel opens resulting in a rapid exchange of ions and a very rapid response

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8
Q

What are G protein-coupled receptors

A

Receptors that are associated with G-proteins, when activated they activate a cascade of intracellular signalling molecules leading to an effect in milliseconds to seconds

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9
Q

Which receptors are the slowest?

A

Enzyme-linked receptors

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10
Q

What is the equation for drug-receptor binding?

A

D+RDR–>Response

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11
Q

Why is the formation of a DR complex reversible?

A

The bonds formed during binding are relatively weak (H-bonding or van der Waals)

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12
Q

What is Ka? (Koff/Kon)

A

A measure of the affinity of the drug for a receptor and can be used as a measure of drug potency

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13
Q

What does it mean for a drug to have high affinity?

A

Smaller amounts of the drug are required to occupy more receptors

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14
Q

What is the units for Ka?

A

Moles L-1

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15
Q

What does a high value for Ka mean?

A

Low affinity, since it is Koff/Kon a high affinity means the DR complex isn’t favoured

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16
Q

What is Kd?

A

Dissociation constant

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17
Q

What is the relationship between Ka and Kd?

A

Kd is the reciprocal of Ka, Kd=1/Ka

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18
Q

What are the 2 conformational states of drug-receptor complexes?

A

Active and inactive

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19
Q

What is the equation for active and inactive DR states?

A

D+RDRDR*

* = active state

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20
Q

What is an agonist?

A

A drug that binds to a receptor that elicits a response

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21
Q

What is an antagonist?

A

A drug that binds to receptor but doesn’t initiate a repsonse

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22
Q

What are the 3 types of agonist?

A

Full, partial and inverse

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23
Q

What is a full agonist

A

An agonist that when bound to a receptor is able to elicit a maximal response

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24
Q

What is a partial agonist?

A

An agonist that when bound to a receptor is incapable of eliciting a maximal response

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25
Q

Why are full agonists able to elicit a maximal response?

A

They stabilise the R* (active state)

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26
Q

Why can partial agonists not elicit a maximal response?

A

They stabilise both the active and inactive state of the receptor and so even though there is full occupancy of the receptors, a maximal response is not reached

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27
Q

What are inverse agonists and how do they work?

A

They reduce the response mediated by full agonists by stabilising the inactive form of the receptor, essentially reduce the normal response percentage as if the drug wasn’t present

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28
Q

What is the most common measurement used to determine whether a drug is a full, partial or inverse agonist?

A

Determining the drugs impact on contraction of ileum in smooth muscle

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29
Q

How do you know from a chart that maximal response has been reached?

A

When 2 or more concentrations of an agonist is added and the response doesn’t increase

30
Q

What is plotted for a concentration-response curve?

A

Agonist concentration against response (log)

31
Q

What is the Emax?

A

Maximum response

32
Q

What is EC50?

A

The agonist concentration that produces half the maximum response

33
Q

Besides EC50, what can also be determined from concentration-response curves indirectly?

A

Efficacy and potency from the receptor occupancy and agonist affinity

34
Q

What effect on the concentration-response curve would a more potent full agonist have?

A

Shifted left

35
Q

Does a more potent drug increase or decrease EC5?

A

Decrease

36
Q

What effect does a partial agonist have on a concentration-response curve?

A

Lower and shifted right, a maximum response is not reached and the potency is reduced

37
Q

What effect does an inverse agonist have on the concentration-response curve?

A

The graph is below the x-axis since the normal response is opposed

38
Q

Give an example of an inverse agonist and its effect

A

Agonists of GABAa receptors give sedative effect, Ro15-4513 has a convulsive (shaking) effect

39
Q

What is the concept behind spare receptors?

A

Only a small amount of receptors need to be activated in order for a response to be made and so a large proportion of receptors are theoretically not needed

40
Q

Why is it useful that only a small amount of receptors are required to be activated in order for a response to be given?

A

Only a small amount of drug is required which helps to reduce the amount of adverse side effects

41
Q

In what situation can a partial agonist be considered as an antagonist?

A

When it is in the presence of a full agonist as it is occupying receptors whilst not eliciting an effect

42
Q

What are the 2 classes of antagonists?

A

Reversible competitive or non-competitive

43
Q

What is a competitive antagonist?

A

An antagonist that binds to the same site on the receptor that the agonist binds to and therefore competes for the binding site

44
Q

How can the effect of an antagonist be overcome?

A

By increasing the concentration of agonist

45
Q

Why do competitive agonists sometimes appear to be irreversible

A

If they dissociate from the receptor very slowly

46
Q

What does a competitive agonist do to the concentration response curve?

A

Shift to the right (more drug is required for response, maximum response can be reached if enough agonist is added)

47
Q

What does a non-competitive antagonist do to the concentration-response curve?

A

Lowers it (maximal response cannot be reached since it binds to a different binding site)

48
Q

What is the site called that a non-competitive antagonist binds to?

A

Allosteric site

49
Q

How can you reverse the effects of a non-competitive antagonist?

A

Wash out the antagonist

50
Q

What does it mean for competitive antagonists being surmountable?

A

Capable of being overcome

51
Q

What is dose ratio

A

The factor by which the concentration of the agonist has to be multiplied by to produce the same response in the presence of antagonist, helps to measure the potency of the antagonist

52
Q

How is the dose ratio worked out?

A

DR = EC50 with antagonist/ EC50 without antagonist

53
Q

Does the EC50 value increase or decrease in the presence of a competitive antagonist?

A

Increase

54
Q

What is plotted in a Schild plot?

A

log(DR-1) against log(antagonist concentration)

55
Q

What values can be determined from a Schild plot?

A

pA2 and Ka for the antagonist

56
Q

What should the gradient of a Schild plot be around for a competitive antagonist?

A

1

57
Q

What is the pA2 value?

A

The negative log of the molar concentration f antagonist that produces an agonist DR of 2. The negative sign and units are dropped

58
Q

How do you find the pA2 value from a Schild plot?

A

X intercept

59
Q

What is the relationship between pA2 and Ka?

A

pA2 = -log Ka

60
Q

How many subunits make up GABAa receptor and what are they?

A

5, 2 alpha, 2 beta and a gamma

61
Q

What type of receptor is GABAa receptor?

A

Ligand-gated ion channel receptor ionotropic

62
Q

What happens when the GABAa receptor is activated by GABA?

A

The Cl- pore opens allowing Cl- to flow into the cell depolarising the membrane (more negative), resulting in the neuron becoming less excitable and so GABA is an inhibitory neurotransmitter

63
Q

How many binding sites on GABAa are there for GABA?

A

2

64
Q

What is the other binding site on GABAa for other than for GABA and where is it?

A

Benzodiazepines, between the gamma and alpha subunit

65
Q

Give an example of a benzodiazepine and what is its drug use?

A

Valium, used to help treat anxiety

66
Q

Why are benzodiazepines positive allosteric modulators?

A

They potentiate the effect of GABA on GABAa receptors, help relax, by increasing the affinity of GABA on GABAa receptors

67
Q

What does synergistic mean?

A

Work in collaboration

68
Q

What does it mean by receptors being dynamic proteins?

A

The number of receptors and their functions on membranes are constantly changing

69
Q

When does receptor desensitisation occur?

A

When receptors are over activated by being exposed to high concentrations of agonist.
Repeated exposure of receptors to agonist with insufficient time intervals

70
Q

What happens in receptor desensitisation?

A

The response for a given concentration of agonist is reduced since receptors are removed from the membrane faster than being replaced resulting in not reaching maximal response

71
Q

When can receptor super sensitivity occur?

A

Long term use of receptor antagonist drugs as this can increase the number of receptors

72
Q

How can receptor super sensitivity be reduced when stopping taking a drug?

A

Slowly stopping the drug treatment by gradually reducing the dose to help prevent adverse side effects

PHAY0003 (22 decks)

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