Membrane receptors

Question 1

4 main types of receptor

Answer 1

ligand-gated ion channels
tyrosine kinase receptors
guanylate cyclase receptors
G protein-coupled receptors

Question 2

Which receptors typically mediate fast responses?

Examples include nicotinic acetylcholine, GABA-A & GABA-C, glutamate receptors

Answer 2

Ligand-gated ion channel receptors

Question 3

Two types of tyrosine Kinase receptor

Answer 3

1. receptor tyrosine kinase
   > insulin, insulin-like growth factor (IGF), epidermal growth factor (EGF)
2. non-receptor tyrosine kinase
   > PIGG(L)ET: Prolactin, Immunomodulators (cytokines IL-2, Il-6, IFN), GH, G-CSF, Erythropoietin and Thromobopoietin

Question 4

contain intrinsic enzyme activity
e.g. atrial natriuretic factor, brain natriuretic peptide

Answer 4

guanylate cyclase receptors

Question 5

• mediate slow transmission and affect metabolic processes
• activated by variety of extracellular signals e.g. Peptide hormones, adrenaline, lipophilic hormones, light
• 7-helix membrane-spanning domains
• 3 main subunits: alpha, beta and gamma

Answer 5

G protein coupled receptor

Question 6

G proteins are named according to the alpha subunit (Gs, Gi, Gq)
Describe the function of each

Answer 6

Gs - STIMULATES adenylyl cyclase

Gi - INHIBITS adenylyl cyclase

Gq - Activates phospholipase C

Question 7

Mechanism of action of Gs receptor

Answer 7

Stimulates adenylate cyclase → increases cAMP → activates protein kinase A

Question 8

Mechanism of action of Gi receptor

Answer 8

Inhibits adenylate cyclase → decreases cAMP → inhibits protein kinase A

Question 9

Mechanism of action of Gq receptor

Answer 9

Activates phospholipase C → splits PIP2 to IP3 & DAG → activates protein kinase C

Question 10

Give examples of Gs receptors

Answer 10

• Beta-1 receptors (epinephrine, norepinephrine, dobutamine)
• Beta-2 receptors (epinephrine, salbuterol)
• H2 receptors (histamine)
• D1 receptors (dopamine)
• V2 receptors (vasopressin)
• Receptors for ACTH, LH, FSH, glucagon, PTH, calcitonin, prostaglandins

Question 11

Give examples of Gi receptors

Answer 11

• M2 receptors (acetylcholine)
• Alpha-2 receptors (epinephrine, norephinephrine)
• D2 receptors (dopamine)
• GABA-B receptor

Question 12

Give examples of Gq receptors

Answer 12

• Alpha-1 receptors (epinephrine, norepinephrine)
• H1 receptors (histamine)
• V1 receptors (vasopressin)
• M1, M3 receptors (acetylcholine)