Theories of Drug Action

Question 1

What are the common characteristics of receptors?

Answer 1

.Selective binding site for endogenous messengers
.Act as molecular switches - inactive and active states
.Signal is amplified

Question 2

List the four main superfamilies

Answer 2

From fast to slow 
Ligand gated ion channels
G protein coupled receptors
Catalytic receptors
Nuclear Receptors

Question 3

Describe the difference in pharmacology between [enzymes, transporters, ion channels] and receptors

Answer 3

[enzymes, transporters, ion channels] effected by one type of drug - inhibitors. Receptors have at least two - agonists and antagonists

Question 4

Define affinity

Answer 4

The ability of a drug to bind its receptor

Question 5

Define efficacy

Answer 5

The ability of a drug, once bound, to activate the receptor by a conformational change

Question 6

True or False? A receptor agonist binds and activates the target, it has both affinity and efficacy

Answer 6

TRUE!

Question 7

True or False? A receptor antagonist binds and blocks messenger responses, it has both affinity and efficacy

Answer 7

False! It only has affinity

Question 8

How do we obtain numbers that estimate affinity?

Answer 8

Rates of binding are proportional to CONCENTRATION
Forward rate = kON[D][R]
kON = association constant
Reverse rate = kOFF[DR]
kOFF = dissociation rate constant
At dynamic equilibrium
kD = [D][R]/[DR] as forward rate=reverse rate
kD - concentration of drug needed to occupy 50% of receptors i.e. a measure of its binding affinity