Which receptor types are Gq protein-coupled?

• A. M1 receptor type
• B. M2 receptor type
• C. M3 receptor type
• D. M1 and M3 receptor types

Answer: (D)

Receptors that couple to Gq activate phospholipase C through the Gq protein, which then splits PIP2 into IP3 and DAG, leading to a rise in intracellular calcium and PKC activation. Among muscarinic receptors, the M1 and M3 types use this Gq pathway, while the M2 type signals through Gi/o and lowers cAMP. Because the question asks which receptor types are Gq-coupled, M1 and M3 together cover the receptors that use this pathway. (M5 is also Gq-coupled, but it’s not listed here.)