L5 - Quantitative receptor pharmacology pt2

Question 2

SPIKES binding analysis

Answer 2

a stepwise approach for
analysing competition binding
curves and determining which
receptors are present in a cell.
Shape of curve, Position of curve, IC50, Ki, Elimination, Summation

Question 3

S

Answer 3

If the curve is steep sigmoidal: Ligand A is binding to receptors for which it has similar affinity

If the curve is shallow sigmoidal or biphasic: Ligand A is binding to
receptors for which its affinities are
NOT all the same

Question 4

PIK - Steep sigmoidal

Answer 4

IC50 is clear
Ki value can be calculated from IC50

Question 5

PIK - biphashal

Answer 5

IC50 values can be generated for
each phase (high & low affinity)

If each phase is STEEP sigmoidal
then each IC50 value can be used to calculate a Ki value

Question 6

PIK - Shallow sigmoidal

Answer 6

a single IC50 value can be
generated by eye, it cannot be used to calculate the multiple Ki values

must fit data to 2-site binding model to derive 2 Ki values, that can be
used for elimination & summation

Question 7

E

Answer 7

Elimination
If the calculated –log Ki value is
>1 unit different from the known–log Ki value of the ligand for any receptor then that receptor is deemed unlikely to be expressed by the cell

Question 8

S