Receptor theory 3 Flashcards
What is suggested if a saturation point is not reached in a ligand binding assay
Non specific binding is occurring
What shape does specific binding show on a logarithmically scaled ligand binding assay graph
Sigmoidal curve - non specific remains level until very high concentrations where it rises exponentially
What is the drug concentration that occupies 50% of the receptors equal to?
Kd
What is on the Y axis of the scatchard plot
Bound radioligand/ free radioligand
What is on the X axis of the scatchard plot
Bound radioligand
What does the X intercept define
Bmax - Maximum amount of drug
What is the slope of the line equal to
-1/Kd
What happens to the occupancy - concentration graph if the affinity is high
Shifted to the right
Give two examples example for when measuring affinity can indicate differences between receptors for the same ligand
Morphine side effect of constipation - Gut opiate receptors that control motility- Opiate receptors in the brain and spinal cord for pain - Different receptors due to different affinity for morphine
Muscarinic receptors - The differing affinity of sympathetic ganglia and sublinguinal gland mAchRs have differing affinities to pirenzepine - pirenzepine shows selectivity for sympathetic ganglion receptors
What is EC50
The concentration of drug needed to give 50% of the maximal response
How is possible to get an EC50 at a lower drug concentration than needed to occupy 50% of the receptors
Because there is a receptor reserve - more receptors present than needed to produce a maximal response
Common in the gut - need to occupy 5% to elicit maximum response
How is potency used to compare agonists
Concentration response graphs show the drug with the curve furthest to the left has the highest potency
What is suggested if an agonist has the same EC50 as another but cannot elicit a maximal response
It is a partial agonist - they have a lower efficacy than a full agonist
