Think about these two facts: a) The alpha-subunit of the G-protein trimer has an intrinsic GTPase activity, which is important in terminating the action of G-protein coupled systems.  b) The CFTR is activated by cAMP.  Here’s the question: If you introduced a toxin into the intestinal cell that blocks the intrinsic GTPase activity of a stimulatory G-protein (Gs), what would be the most significant effect on intestinal function?  Briefly explain the mechanism underlying your answer, including the most important steps in the signal transduction pathway.