L5 - measurement of drug activity at receptors

Question 1

what is the problem with the curve of bound radioactivity vs concentration of labeled drug for radioligand binding assay

Answer 1

no rectangular hyperbola shape. the curve doesn’t plateau as receptors are occupied

Question 2

why is the radioligand binding assay curve different for first tube

Answer 2

there is no sign of saturation because we are measuring a mix of specific and non-specific binding. this is called total binding

Question 3

what is the second set of tubes for in radioligand binding assays

Answer 3

to reduce the amount of non-specific binding that is prominent in the first set of tubes.
second set is prepared with radiolabled and non-radioactive (cold) drug.

Question 4

what is the purpose of using cold drug during radioligand binding assay

Answer 4

gives a plot of non-specific binding against concentration because the cold drug has taken up all the receptor spaces

Question 5

how do we get a measure of specific binding in radioligsand binding assay

Answer 5

subtract non-specific binding from total binding

Question 6

what is the dose ratio

Answer 6

ratio of the concentration of agonist producing the same sized response in the presence and absence of the antagonist.

Question 7

what is the pA2

Answer 7

negative log of the molar concentration of antagonist that produces a dose ratio of 2.
the affinity of a reversible competitive antagonist.

Question 8

what is the schild equation

Answer 8

log (dose ratio-1) = log (antagonist concentration) - logKb

Question 9

what is Kb

Answer 9

equilibrium dissociation constant for an antagonist
pA2 = pKb

Question 10

what must the gradient of the schild plot be

Answer 10

1