lecture 5 - mechanisms of drug action

Question 1

describe 4 main sites of drug actions

Answer 1

• receptor
• ion channels
• enzymes
• transporters

Question 2

describe affinity

Answer 2

a measure of how tightly a drug binds to the receptor
if a drug doesnt bind well the action will be shorter

measured by using dissociation constant = Kd

Question 3

define Kd

Answer 3

conc of a drug when 50% of receptors are occupied

higher the Kd the lower the affinity of the drug (more drug it’ll take to bind to the receptors)

Question 4

describe potency

Answer 4

measure of how much drug is required in order to produce a particular effect
conc of drug required to produce 50% of maximal response = (EC50)

high potency = small amount required to induce large response e.g. lower EC50

Question 5

describe efficacy

Answer 5

ability of a drug to produce a response e.g. bind to a receptor and cause a change in receptor action

positive efficacy = agonist
negative efficacy = inverse agonist
no efficacy = antagonist, prevents agonist effect

Question 6

describe angonists

Answer 6

agonist are described as having affinity and efficacy, partial agonists are drugs which bind with affinity, but don’t produce maximal response (even at 100% occupancy)

Question 7

describe antagonist

Answer 7

drugs which have no intrinsic efficacy - they can bind to receptors (affinity) but dont induce a conformational change in the receptor. Produce their effects by preventing agonist from binding.

Question 8

describe ligand-gated ion channels

Answer 8

• fast synaptic signalling
• binding of neurotransmitters to this receptor causes immediate conformational change that opens channel portion of protein

Question 9

describe G protein-coupled receptors

Answer 9

• slow synaptic signalling
• time course slower e.g. regulation of heart rate, requires a slower neurotransmission
• longer signalling pathway

Question 10

describe carrier/transport molecules and give an example

Answer 10

• transportation of polar molecules across lipid membranes often requires carrier protein
• drug target often blocks this transporter

example: SSRIs for depression

Question 11

describe ion channels and give an example

Answer 11

• protein molecules that span the cell membrane, and can switch between open and closed states, allowing the controlled entry and exit of specific ions across the cell membrane.
• highly selective

example: local anaesthetics are a class of drugs that block pain pathways by blocking voltage gated sodium channels and therefore preventing AP that carry pain signals