In the below graph label the trace that shows CAMP concentra

In the below graph, label the trace that shows CAMP concentrations in (1) normal intestinal epithelial cells and (2) cholera toxin treated cells. Explain your reasoning

Solution

Answer:

1. Normal intestinal epithelial cells - Solid line

2. Cholera toxin treated cells - Dotted line

When cholera toxin penetrates the cell membrane and reaches the cytosol, it catalyzes addition of ADP-ribose moiety from intracellular NAD⁺ to Gs. ADP-ribosylated Gs-GTP can activate adenylyl cyclase but cannot hydrolyze GTP to GDP. So, Gs remains activated resulting in continuous activation of adenylyl cyclase.

This results in the increase of cAMP concentrations to more than 100 fold in intestinal cells which causes massive inflow of water from blood into the intestinal lumen.

In case of normal intestinal cells, the activation of adenylyl cyclase is limited, thus cAMP level comes down after some time.