Heterologous desensitization

• A. Adding an antagonist for receptor B desensizes receptor A
• B. Adding an agonist for receptor A, desensizes receptor B
• C. It only occurs in in vitro conditions
• D. It increases sensitivity of receptor B to its ligand

Answer: (B)

Heterologous desensitization occurs when activating one receptor type (receptor A) reduces the responsiveness of a different receptor type (receptor B) through shared intracellular signaling pathways. When receptor A is stimulated by its agonist, its signaling activates kinases such as GRKs and downstream effectors like PKA or PKC. These kinases can phosphorylate receptor B or otherwise disrupt its signaling machinery, making receptor B less responsive to its own ligand. This cross-talk happens in living systems as well as in controlled settings, so it’s not limited to in vitro conditions. The best description is that activating receptor A desensitizes receptor B, not that antagonizing B or increasing B’s sensitivity would produce this effect.