Drug Affinity Flashcards
What is a constant in drug receptor theory
affinity of drug for receptor
How can affinity of a drug be determined
ligand binding assays
What is affinity
how tightly the drug and receptor interact
What is the measurement of affinity
KD
When is KD measured
at equilibrium
Describe the relationship between KD and affinity
inverse relationship
Describe the affinity if the KD value is low
high affinity
What is KD
Concentration of drug required to occupy 50% of receptors
Why is the relationship between KD and affinity inverse
the better the drug is at binding the lower the conc to occupy receptors
What is the efficacy value for agonists
high
What type of drug has no response of efficacy
antagonists
What does efficacy govern
activation
What is EC50
effective concentration giving 50% of maximal response
What is the receptor reserve
spare receptors
What can efficacy of an agonist influence
size of response
What does ACh bind to (guinea-pig ileum)
GPCR muscarinic receptor
What happens when ACh binds to GPRC muscarinic receptors (guinea-pig ileum)
Gq proteins activate, generate a second messenger
What does the second messengers trigger (guinea-pig ileum)
rise in intracellular calcium
What does the rise in intracellular calcium trigger (guinea-pig ileum)
activation of contractile machinery - contraction
What is drug concentration to response curves plotted on
semi logarithmic scale
What does the sigmoidal curve hill equation fit to
concentration response curve
What value does the Hill slope tend to be
around 1
When would you have two agonists bind at once
nicotinic receptors
What does the hill slope value tend to be when two agonists bind
around 2
Describe the relationship between drug potency and EC50
low EC50 values are more potent
Describe the relationship between affinity and potency
as affinity increases potency increases
What factors determine potency
affinity, efficacy and spare receptors
What is the efficacy of partial agonists
partial agonists have an efficacy less than 1
What is KD value the same as for partial agonists
KD=EC50
What is the efficacy of full agonists
1
What is the efficacy a measure of
a single agonist receptor complex’s ability to generate a response
What properties determine the effect of a drug in a living system
specificity, affinity, efficacy
What can vary between different tissues
EC50
