A 32 yr. old female is suffering from watery diarrhoea, hyponatremia and hypokalemia. Later it was diagnosed as cholera. The mechanism of action of heat labile toxin of Vibrio cholerae is
A 32 yr. old female is suffering from watery diarrhoea, hyponatremia and hypokalemia. Later it was diagnosed as cholera. The mechanism of action of heat labile toxin of Vibrio cholerae is
💡 Explanation
## **Core Concept**
The heat-labile toxin (LT) of *Vibrio cholerae* is a key virulence factor that causes the characteristic watery diarrhea of cholera. This toxin acts by stimulating the secretion of chloride and bicarbonate into the intestinal lumen, leading to a massive efflux of water and electrolytes. The mechanism involves the activation of adenylate cyclase in the intestinal epithelial cells.
## **Why the Correct Answer is Right**
The heat-labile toxin of *Vibrio cholerae* mimics the action of **choleragen**, which activates **Gs alpha subunit** of the G protein complex in the intestinal epithelial cells. This activation leads to an increase in **intracellular cyclic AMP (cAMP)** levels. Elevated cAMP levels stimulate the **chloride channels** (e.g., CFTR - cystic fibrosis transmembrane conductance regulator) to open, causing chloride to be secreted into the intestinal lumen. Water and sodium follow chloride passively, resulting in the characteristic watery diarrhea and leading to **hyponatremia** and **hypokalemia**. This matches option .
## **Why Each Wrong Option is Incorrect**
- **Option A:** This option suggests an inhibition of adenylate cyclase, which would decrease cAMP levels and is contrary to the action of the heat-labile toxin of *Vibrio cholerae*.
- **Option B:** This option refers to the action of the heat-stable toxin (ST) of *E. coli*, which increases **guanylate cyclase** activity and **cGMP** levels, not related to the mechanism of cholera toxin.
- **Option D:** This option suggests an increase in **phospholipase C** activity, which is involved in another signaling pathway that does not pertain to the action of cholera toxin.
## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the mainstay of treatment for cholera is **oral rehydration therapy (ORT)**, which replaces lost fluids and electrolytes. The effectiveness of ORT in treating cholera and similar diarrheal diseases has been a significant advancement in public health.