Which mechanism best describes how metabotropic receptors produce slower, longer-lasting effects?

• A. They form ion channels directly.
• B. They activate G proteins and second messenger cascades.
• C. They are fast ligand-gated channels.
• D. They cause immediate depolarization through Na+ influx.

Answer: (B)

Metabotropic receptors produce slower, longer-lasting effects because they work through intracellular signaling rather than forming an ion channel themselves. When a neurotransmitter binds, the receptor activates a G protein, which then triggers second messenger cascades such as cAMP or IP3/DAG. These messengers modulate enzymes, open or close ion channels indirectly, and can alter gene expression, leading to effects that develop over seconds to minutes and can last longer. This contrasts with ionotropic receptors, which are ligand-gated ion channels that open quickly to produce fast depolarizing or hyperpolarizing currents. So the best description is the activation of G proteins and second messenger cascades.