Cholera toxin acts by –
**Core Concept**
Cholera toxin is an exotoxin produced by *Vibrio cholerae*, causing the disease cholera. It acts on the intestinal epithelial cells, leading to a profound secretory diarrhea. The toxin's mechanism involves altering signaling pathways in these cells.
**Why the Correct Answer is Right**
Although the exact correct answer choice is not provided, the mechanism of cholera toxin typically involves the activation of **adenylate cyclase** via the toxin's A subunit, which in turn increases the levels of **cyclic AMP (cAMP)** within the intestinal epithelial cells. This increase in cAMP leads to the secretion of chloride and bicarbonate into the intestinal lumen, followed by the movement of sodium and water, resulting in the characteristic watery diarrhea of cholera.
**Why Each Wrong Option is Incorrect**
**Option A:** Would be incorrect if it suggested a mechanism not involving the increase of cAMP or direct action on the intestinal epithelium.
**Option B:** Might be incorrect if it proposed a different signaling molecule or pathway not primarily involved in cholera toxin's action.
**Option C:** Could be wrong if it implied a direct effect on the intestinal musculature or a different cellular target.
**Option D:** Would be incorrect if it described an immune-mediated response rather than a direct toxic effect on intestinal cells.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that cholera toxin's action can be treated with oral rehydration therapy, focusing on replacing lost fluids and electrolytes. The toxin itself does not cause inflammation or damage to the intestinal lining, making rehydration highly effective.
**Correct Answer:** D. Increasing cAMP.