Explain the difference between ion channel receptors and G-protein coupled receptors in terms of signaling speed and mechanism.

• A. Ion channel receptors mediate rapid, direct ion flux changes; GPCRs activate second messenger cascades via G proteins, producing slower but amplified responses.
• B. Ion channels activate second messengers; GPCRs directly transport ions.
• C. Both types signal at the same speed through identical mechanisms.
• D. GPCRs open ion channels directly and instantaneously.

Answer: (A)