Metabotropic receptors are associated with what signaling proteins?

• A. Ion channels
• B. G-protein coupled receptors
• C. Enzymes
• D. G-proteins

Answer: (D)

Metabotropic receptors transmit signals through intracellular G-proteins. When a ligand binds, the receptor—being a G-protein-coupled receptor—activates a heterotrimeric G-protein. The G-protein’s alpha subunit exchanges GDP for GTP and dissociates from the beta-gamma complex, then both portions regulate downstream effectors such as adenylyl cyclase or phospholipase C, generating second messengers like cAMP, IP3, and DAG. This indirect pathway contrasts with ion channels that are directly gated by ionotropic receptors. Therefore, the signaling proteins most closely associated with metabotropic receptors are G-proteins, which coordinate the intracellular cascade leading to diverse cellular responses.