Receptors and Membrane Signalling

Question 1

What is the law of mass action?

Answer 1

A+R = AR
Kd = [A][R] / [AR]    Kd is the dissociation constant and defines the point of equilibrium 
Units = mols/litre

If there is a fixed number of receptors
[Rt] = [R] + [RA]
p means occupancy
p= [AR]/[Rt] = A/ Kd + [A]

Question 2

What different drug receptors are there?

Answer 2

Enzymes
Ion channels
Transporters (pumps)
“Physiological” receptors (receptors for hormones, neurotransmitters, etc).

Question 3

What are the ways of regulating cell function?

Answer 3

1. Altered membrane potential
2. Altered enzyme activity
3. Altered gene expression
   Most drugs affect these cell functions via (physiological) receptors

Question 4

How are receptors classified?

Answer 4

Receptors are classified on the basis of the selective action of drugs.
They are named according the transmitter or hormones with which they interact.
Most hormones interact with more than one type of receptor.

Question 5

What are the receptor “superfamilies”

Answer 5

1. Integral ion channel
2. Integral tyrosine kinases
3. Steroid receptors
4. G protein coupled receptors
5. Cytokine receptors

Question 6

What is the effect on the number of spare receptors with highly efficacious agonists?

Answer 6

Some highly efficacious agonists can produce a maximal response from the cell without binding to all available receptors.

Question 7

What is the effect on the cell when a partial agonist binds to its receptors?

Answer 7

Partial agonists have a low efficacy. It cannot produce the cell’s maximal response, even when they have bound to all of the available receptors.