A 24-year-old man returns from a flood relief camp with painless profuse rice-water diarrhoea. Stool culture grows Vibrio cholerae. The enterotoxin causes secretion by which mechanism on intestinal crypt cells?

• A Direct opening of tight junctions between enterocytes, causing paracellular leak
• B Blockade of the Na+-glucose cotransporter SGLT1 on villous enterocytes
• C ADP-ribosylation of the Gs alpha subunit, sustained cAMP rise, and activation of CFTR chloride channels ✓
• D Inhibition of the basolateral Na+/K+-ATPase, collapsing cellular ion gradients

Explanation

Cholera toxin ADP-ribosylates Gs-alpha, locking it in the active state, so adenylyl cyclase keeps generating cAMP. Protein kinase A then phosphorylates and opens apical CFTR channels, driving Cl- into the lumen; Na+ and water follow, producing secretory diarrhoea. SGLT1 remains intact, which is why oral rehydration with glucose works.

Reference: Guyton and Hall Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.