Receptor Interaction Flashcards
What is an agonist vs an antagonist
Agonist - activates
Antagonist - blocks action
What’s forward rate ? What does it depend on?
Depends upon concs of D and R in system
What is backwards rate? What does it depend on?
Depends mainly upon the affinity of D for R
What is Ka ?
Acid dissociation constant
What is the formula for Ka?
Ka= [D] [R] / [DR]
The lower the Ka the higher the affinity, units:moles
What is the occupancy formula ?
[number of receptors occupied]/[total number of receptors]
Ka is numerically equal to what
Equal to the concentration of drug at which half receptors are occupied
- axis might be a log plot so calc antilog
Where is a low Ka to a high Ka ?
Low shifts to left and high shifts to right
Give a system to determine Drug and receptor relationships
Organ bath
Describe a dose response curve
- used to plot extent of response vs drug
- look like occupancy curve (plateau)
What can you tell from a dose response curve ?
- cannot determine Ka from curve
- cant assume = to occupancy
- can determine estimate EC50
Draw a graph for a full and partial agonist
Describe an antagonist (competitive) (5)
- bind to receptor like agonist
- compete for same receptors as cognate antagonist
- dont activate receptor
- prevent agonist from occupying receptor
- intrinsic efficacy of 0
What is intrinsic efficacy ?
Capacity of a drug to activate or inactivate a receptor
What do competitive anatagonists do to DR curves ?
Shift curves to right
How is the potentcy of a drug calculated?
-comparative D/R data
- Schlid plot and pA2 values
- compares shifts in EC50 values
What is the definition of pA2
-log10 (molar concentration id an antagonist which reduces the effect of a double dose of an agonist to that of a single dose
What does a schild plot tell us about?
- straight line with a slope of -1 = competitive antagonism
- pA2 measures antagonist potentcy
What does an irreversible competitive antagonist do ?
Compete for same R as agonist
Doe not dissociate from R
Reduces R therefore reduces maximal response to agonist (Emax)
What is an IC50 value ?
Concentration of an inhibitor that reduces a response or bio. Process by 50% of the maximum
What does acetylcholine do ?
Reduces HR in dose dependent manner
By stimulating muscarinic receptors in the heart
What does phenalzine do ?
Inhibits enzyme that breaks down adrenaline
What does propranolol do ?
Reduces HR in dose dependent manner by blocking beta-adrenoceptors in the heart
What can IC50 values be compared to ?
EC50 to compare drug potentcies
