What is the primary effect of down-regulation on receptors?

• A. Increases the cell's sensitivity to signals.
• B. Decreases the number of active signals received.
• C. Enhances cell proliferation.
• D. Facilitates faster signal transduction.

Answer: (B)

Down-regulation of receptors primarily results in a decrease in sensitivity to signals, which can lead to a reduction in the number of active signals that the cell receives. This process typically occurs when a cell is exposed to high levels of a signaling molecule over time. As a compensatory mechanism, the cell may reduce the number of receptors available on its surface, thereby decreasing the overall responsiveness to that signaling molecule. This adaptation helps prevent overreaction to persistent stimuli and maintains cellular homeostasis.

In this context, if the receptor numbers are reduced, there will inherently be fewer opportunities for those receptors to bind their ligands, resulting in decreased overall signaling activity. This is a normal cellular response to chronic stimulation and is important for regulating various physiological processes.