Receptor Mechanism I

Question 1

What are the 4 main families of receptors?

Answer 1

• ligand-gated ion channels
• G-protein coupled receptors
• kinase-linked receptors
• nuclear receptors

Question 2

Which is the fastest family of receptors?

Answer 2

The fastest are ligand-gated ion channels. their message is sent across in milliseconds.

Question 3

Name 4 ligand-gated ion channels and their agonists (what they’re stimulated by).

Answer 3

• Nicotinic Cholinoceptor (stimulates by Acetylcholine)
• 5HT3 (stimulated by 5-HT, serotonin)
• GABA(A) (stimulated by γ-amino butyric acid (GABA))
• Glycine receptor (stimulated by Glycine)

Question 4

For the 4 ligand-gated ion channels, list the ions involved and what their effect is on the membrane potential.

Answer 4

For the Nicotinic and 5HT3, the ions are Na/Ca, and it depolarises the cell.
For GABA(A) and Glycine, the ion is Cl, and it hyperpolarises the cell.

Question 5

Describe the structure of ligand-gated ion channel receptors.

Answer 5

One subunit consists of a large extracellular N-terminal domain (this is has the ACh binding site), four transmembrane segments (TM1-TM4) and a short extracellular C-terminal.
Five subunits make up a ligand-gated ion channel. TM2 forms the lining of the ion pore.

Question 6

How many acetylcholine molecules are needed to activate the nicotinic receptor?

Answer 6

Two.

Question 7

How are the subunits of the receptor stored (in the membrane)?

Answer 7

It’s stored in a way that the hydrophobic parts are within the membrane, while the hydrophillic parts are outside of the membrane.

Question 8

What are the different places that nicotine-type acetylcholine receptors are found (and what kind of receptors do they contain)?

Answer 8

They are found in the:

• Skeletal muscle (N1 or Nm)
• CNS (N2 or Nn)
• Autonomic ganglia (N2 or Nn)

Question 9

With N1 receptors, give two examples of their AChRs, including their subunits.

Answer 9

• muscle nicotinic AChRs (adult neuromuscular junction)
  α1 - ε - α1 - β1 - δ
• muscle nicotinic AChRs (foetal extrajunctional)
  α1 - γ - α1 - β1 - δ

The only difference in subunit structure between the adult and foetal AChR is the ε and the γ. However, this affects how they work. Foetal receptor activity is more sluggish and stays open longer. We will actually change the protein made as we get older, changing the subunit.

Question 10

Give an example of an N2 receptor.

Answer 10

• neuronal nicotinic AChRs

α2 - α8 and β2 - β4

Question 11

Give the name of the disease for when muscle nicotinic AChRs become degraded, and describe it.

Answer 11

The disease is called MYASTHENIA GRAVIS. It's an autoimmune disease that targets the α1 subunit in the receptors. This is why the neuronal nicotinic AChR is unaffected.
The symptoms are:
-droppy eyelids
-fatigue
-diffuculty swallowing/talking
-exertion is diffuclt

Question 12

What is the difference in stimulating the nicotinic-AChR and the GABA(A) receptor?

Answer 12

The stimulation of nicotinic-AChRs in skeletal muscle CONTRACTS the muscle quickly. The 2 acetylcholine molecules bind to the alpha binding sites each, causing a conformational change, opening up the ion pore, allowing Na+ ions inside, depolarising the cell.

The stimulation of GABA(A) receptors in neurones INHIBITS activity quickly. The inhibitory nerves release GABA or glycine, allowing the Cl- ions to enter, hyperpolarising the cell.

Question 13

What are MEPPS and how are they formed?

Answer 13

MEPPS are Miniture End Plate Potentials.

They come about when there are random collisions of ACh vessicles with the membrane.

Question 14

What are the 2 types of receptors ACh binds to and at what speed do you get a ar response?

Answer 14

• Nicotinic - Fast response, LGICR

- Muscarinic - slower response - GPCR