Question

Which of the following receptors is coupled to the stimulatory G protein (Gs)?

• A. M2 muscarinic receptor
• B. M1 muscarinic receptor
• C. Beta-adrenergic receptor
• D. Alpha-2-adrenergic receptor

Hint:

Which catecholamine receptor raises cAMP?

Answer 1

The Correct Option is C

Step 1: Recall G-protein coupling.
Gs (stimulatory) activates adenylyl cyclase and raises cyclic AMP. Gi (inhibitory) lowers cAMP. Gq activates phospholipase C, raising IP3/DAG and intracellular calcium.

Step 2: Classify each receptor.
Beta-adrenergic receptors (beta-1, beta-2, beta-3) are the classic Gs-coupled receptors, increasing cAMP. M2 muscarinic and alpha-2-adrenergic receptors are Gi-coupled (decrease cAMP). M1 (and M3/M5) muscarinic receptors are Gq-coupled.

Step 3: Choose the Gs receptor.
Only the beta-adrenergic receptor uses Gs.

Key fact: Beta-adrenergic = Gs; M2 and alpha-2 = Gi; M1 = Gq.