Desensitization in receptor signaling results in

• A. Increased sensitivity
• B. Decreased responsiveness to persistent stimulation
• C. Upregulation of receptor numbers
• D. Immediate cell death

Answer: (B)

Desensitization in receptor signaling means the cell becomes less responsive after ongoing exposure to the ligand. Mechanistically, receptors—especially GPCRs—are often phosphorylated by kinases and bound by arrestins, which uncouple the receptor from G proteins and can promote receptor internalization. This uncoupling and internalization reduce the ability of the receptor to initiate signaling, so the response diminishes even though the ligand is still present. Over time, receptors may be recycled or degraded, but the key outcome of desensitization is decreased responsiveness to persistent stimulation. The other possibilities—increased sensitivity, upregulation of receptor numbers, or immediate cell death—do not describe what desensitization typically does to receptor signaling.