L5: Measuring of drug action

Question 1

What are radioligand binding assays?

Answer 1

Used to measure the ligand binding to the receptor

Question 2

First step of measuring affinity

Answer 2

Emulsify a brain & divide equally between 2 set of test tubes

Question 3

Second step of measuring affinity

Answer 3

Incubate samples in 1st set of test tubes with varying concentrations of radio labelled RELAXIN

Question 4

Third step of measuring affinity

Answer 4

Filter & wash samples to leave behind relaxin bound to brain tissue

Question 5

Last step of measuring affinity

Answer 5

Measure amount of radioactivity (bound relaxin) per sample

Question 6

What is the total binding mixture?

Answer 6

Mix of specific binding (receptors) & non-specific binding (brain homogenates)

Question 7

1st step to only achieve specific binding

Answer 7

Incubate samples in 2nd set of tubes with same conc of relaxin PLUS large excess of non-radioactive “cold” relaxin

Question 8

How to measure specific binding?

Answer 8

Total binding - nonspecific binding

Question 9

Define Bmax

Answer 9

Max no. of receptors per tissue

Question 10

Define KD

Answer 10

Affinity of the radiolabelled drug

Question 11

Function of reversible competitive antagonists

Answer 11

Inhibits effects of a neurotransmitter/hormone

Question 12

How can effects of the reversible competitive antagonists be overcome?

Answer 12

Increasing the concentration of the antagonist

Question 13

Define dose-ratio

Answer 13

How many times you increase the agonist concentration to overcome blockage

Question 14

How should the dose-ratio increase in terms of reversible competitive antagonist?

Answer 14

Increase in direct proportion to the concentration of antagonist

Question 15

What is pA2 a measure of ?

Answer 15

A measure of the affinity of a competitive antagonist for its receptor

Question 16

Define pA2

Answer 16

Negative log of the molar conc of antagonist that produces a dose ratio 2

Question 17

How to obtain the pA2?

Answer 17

Constructing log conc-response curves for agonist in presence of several concs of antagonists- to allow pA2 to be calculated by ‘Schilds Analysis’

Question 18

What is the Schild equation?

Answer 18

log (dose ratio -1) = log (antagonist conc) - log KB

Question 19

Is pKB equal to pA2?

Answer 19

Yes

Question 20

Step 1 to producing a Schild plot

Answer 20

Construct (log) conc-response curves to agonist in presence of several concs of antagonist- then read log EC50 values for agonist, and calculate them in the absence & presence of different concs of antagonists

Question 21

Equation for dose ratio

Answer 21

Presence of antagonist / Presence of agonist