The physiological effects of epinephrine should in principle be mimicked by addi

Question

The physiological effects of epinephrine should in principle be mimicked by addition of cAMP to the target cells. In practice, addition of cAMP to intact target cells elicits only a minimal physiological response. Why? Write within the box. Anything outside the box will not be graded nor will anything that is illegible or ungrammatical. When the structurally related compound dibutyryl cAMP shown below is added instead, the expected physiological response is readily apparent. Explain the basis for the difference in cellular response to these two substances. Dibutyryl cAMP is widely used in studies of cAMP function. Write within the box. Anything outside the box will not be graded nor will anything that is illegible or ungrammatical.

Explanation / Answer

The concept behind both the questions is the passage of cAMP across the plasma membrane. cAMP cannot enter readily in the intact target cells. cAMP is the second messenger and mimics the action of hormone epinephrine. So theoretically it is alright to assume that it will exhibit similar response as epinephrine. But practically you will observe minimal physiological response because cAMP could not readily cross the plasma membrane as epinephrine.

When you compare the rate of transfer (across the plasma membrane) between the structurally related derivative of cAMP i.e. dibutyryl cAMP and cAMP, it is observed that dibutyryl cAMP can cross the plasma membrane more readily than cAMP. Inside the cell, the butyryl group of dibutyryl cAMP is separated and cAMP generated. Hence, we can observe the physiological response more readily than the addition of cAMP. But the use of dibutyryl cAMP results in accumulation of butyric acid in the cell.

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