Which example illustrates the integrative effect of receptors?

Which example illustrates the integrative effect of receptors?

• A. Receptors with identical G-proteins produce the same effect
• B. Two identical receptors with different G-proteins produce opposite effects on cAMP
• C. Desensitization mechanisms
• D. Receptor downregulation

Answer: (B)

The idea being tested is how signaling from receptors can be integrated when different downstream pathways influence the same second messenger in opposing directions. In this example, two identical receptors couple to different G proteins. One pathway activates adenylyl cyclase through a Gs protein, raising cAMP, while the other pathway inhibits adenylyl cyclase via a Gi protein, lowering cAMP. When both receptors are activated, their signals converge on the same target (cAMP) but push it in opposite directions, so the cell’s final response is a result of this integration and balance between the two effects. Desensitization and downregulation are regulatory processes that reduce receptor responsiveness or receptor numbers, not the integration of signals at the level of second messengers. If identical receptors coupled to the same G protein were activated, you’d still get a consistent effect rather than opposing inputs, which wouldn’t illustrate integration in the same way.

The idea being tested is how signaling from receptors can be integrated when different downstream pathways influence the same second messenger in opposing directions. In this example, two identical receptors couple to different G proteins. One pathway activates adenylyl cyclase through a Gs protein, raising cAMP, while the other pathway inhibits adenylyl cyclase via a Gi protein, lowering cAMP. When both receptors are activated, their signals converge on the same target (cAMP) but push it in opposite directions, so the cell’s final response is a result of this integration and balance between the two effects.

Desensitization and downregulation are regulatory processes that reduce receptor responsiveness or receptor numbers, not the integration of signals at the level of second messengers. If identical receptors coupled to the same G protein were activated, you’d still get a consistent effect rather than opposing inputs, which wouldn’t illustrate integration in the same way.