Lectures 3 and 4

Question 1

Agonist

Answer 1

Drug that binds to and activates receptor

Can be full, partial or inverse

Question 2

Allosteric modulator

Answer 2

Drug that binds to receptor at a site distinct from the active site. Induces a conformational change in the receptor, which alters the affinity of the receptor for the endogenous ligand.

Question 3

Antagonist

Answer 3

A drug that attenuates the effect of an agonist

Can be competitive or non-competitive, each of which can be reversible or irreversible

Question 4

Bmax

Answer 4

The maximum amount of drug or radioligand, usually expressed as picomoles per mg protein, which can specifically bind to receptors in a membrane preparation

Question 5

Cheng-Prusoff equation

Answer 5

Used to determine the Ki value from an IC50 value measured in a competition radioligand binding assay

Question 6

Desensitisation

Answer 6

A reduction in response to an agonist while it is continuously present at the receptor

Question 7

EC50

Answer 7

The molecular concentration of an agonist that produces 50% of the maximum possible response for that agonist

Question 8

ED50

Answer 8

Dose of drug that produces 50% of its maximum response or effect

Question 9

Efficacy

Answer 9

The way that agonists vary in the response they produce when they occupy the same number of receptors

High efficacy agonists produce their maximal response while occupying a relatively low proportion of the total receptor population

Lower efficacy agonists do not activate receptors to the same degree and may not be able to produce the maximal response

Question 10

Half life

Answer 10

Important pharmacokinetic measurement

Time taken for a drug’s concentration in plasma to decline to half its original level

Question 11

IC50

Answer 11

Concentration of an agonist or antagonist which produces 50% of its maximum possible inhibition

Question 12

ID50

Answer 12

Dose of a drug needed to cause 50% of the maximum possible inhibition of that drug

Question 13

Kd

Answer 13

The dissociation constant for a radio labelled drug determined by saturation analysis

It is the molar concentration of radioligand which, at equilibrium, occupies 50% of the receptors

Question 14

Ki

Answer 14

The inhibition constant for a ligand, which donates the affinity of the ligand for a receptor

Question 15

Non-specific binding

Answer 15

The proportion of radioligand that is not displaced by other competitive ligands specific for the receptor

Question 16

pA2

Answer 16

Measure of potency of antagonist

It is the negative logarithm of the molar concentration of an antagonist that would produce a 2-fold shift in the concentration response curve for an agonist

Question 17

p before abbreviation

Answer 17

Negative logarithm

Question 18

Specific binding

Answer 18

The proportion of radioligand that can be displaced by competitive ligands specific to the receptor

Question 19

LGIC

Answer 19

Ionotrophic
Typically at site where fast NTs act
Eg. GABA, nAchR, Glu

Question 20

Structure of LGIC

Answer 20

Homo or hetero

3-5 subunits around central pore

Question 21

Families of LGIC

Answer 21

Cys loop type- pentamers eg nAchR

NMDA type- tetramers

P2X type- trainers
Eg P2XR

Question 22

Why is the gut useful in pharmacology?

Answer 22

Contains many receptors that are the same as those in the brain

Question 23

Propanalol is an example of

Answer 23

Reversible competitive antagonist

Competes with isoprenaline