Lesson 4

G Protein Overview

• Three isoforms of G protein alpha subunits: Gs, Gi, Gq.

Functions of G Protein Isoforms

• Gs: Stimulates adenylate cyclase, increasing cAMP levels.
• Gi: Inhibits adenylate cyclase, decreasing cAMP levels.
• Gq: Activates phospholipase C, increasing IP3, DAG, and intracellular Ca$^{2+}$.

Receptor and Second Messenger Relationships

• Receptor Types:
  • Alpha 1, V1: Gq → Phospholipase C → IP3, DAG, Ca$^{2+}$.
  • Beta 1, Beta 2, Beta 3, M2,4, D1, D2, V2, H2: Gs → Adenylate cyclase → cAMP.
  • M1,3,5, V1, H1: Gq → Phospholipase C → IP3, DAG, Ca$^{2+}$.
  • M2,4, D2: Gi → Inhibition of adenylate cyclase → Decrease in cAMP.

Second Messenger Effects

• Cellular responses to second messengers (IP3, DAG, cAMP) are tissue-specific.
• Recall the specific receptors and their respective second messenger pathways as they are key in physiological functions.