A researcher studies how the hormone epinephrine activates glycogen breakdown in liver cells. She incubates liver slices with: (1) epinephrine, (2) cAMP analog (membrane-permeable), (3) epinephrine + protein kinase A inhibitor, (4) buffer only. Glucose released into the medium is measured after 15 minutes.
Which result would most strongly support the hypothesis that epinephrine acts through a cAMP/PKA pathway?
- A
Only 3 increases glucose
- Bcheck_circle
1 and 2 increase glucose; 3 does not
- C
All four increase glucose equally
- D
Only 4 increases glucose
Explanation
If epinephrine signals through cAMP-activated PKA, then both epinephrine (which raises cAMP) and a cAMP analog should release glucose. Adding a PKA inhibitor with epinephrine should block release, confirming PKA's role in the pathway.