Cholera toxin irreversibly stimulates the cAMP-dependent pump in intestinal cells resulting in
**Core Concept**
Cholera toxin acts by ADP-ribosylating the alpha subunit of the Gs protein, which is a component of the G-protein coupled receptor signaling pathway. This leads to the activation of adenylate cyclase, resulting in an increase in intracellular cyclic adenosine monophosphate (cAMP) levels.
**Why the Correct Answer is Right**
The cholera toxin irreversibly stimulates the cAMP-dependent pump in intestinal cells by activating the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel. This is due to the increased levels of cAMP, which activate protein kinase A (PKA). PKA then phosphorylates and activates CFTR, leading to an increase in chloride secretion into the intestinal lumen. This results in a massive efflux of water and electrolytes from the intestinal cells, leading to the characteristic symptoms of cholera.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because cholera toxin does not stimulate the Na+/K+ ATPase pump. The Na+/K+ ATPase pump is a sodium-potassium pump that helps maintain the resting membrane potential and is not directly involved in the pathogenesis of cholera.
**Option B:** This option is incorrect because cholera toxin does not stimulate the paracellular pathway. The paracellular pathway refers to the movement of ions and water through the tight junctions between intestinal cells, which is not directly affected by cholera toxin.
**Option C:** This option is incorrect because cholera toxin does not inhibit the CFTR chloride channel. In fact, cholera toxin activates the CFTR chloride channel, leading to an increase in chloride secretion into the intestinal lumen.
**Clinical Pearl / High-Yield Fact**
It's worth noting that the effects of cholera toxin can be reversed with the use of antibiotics, such as doxycycline, which can help to eliminate the Vibrio cholerae bacteria from the gut. Additionally, the use of oral rehydration therapy is a critical component of cholera treatment, as it helps to replace lost fluids and electrolytes.
**Correct Answer: D. Chloride secretion into the intestinal lumen.**