Cholera toxin causes massive secretory diarrhoea. The intracellular sequence responsible for the fluid loss is:

• A Inhibition of phosphodiesterase, raised cGMP, activation of basolateral Na+/K+-ATPase in villous cells
• B ADP-ribosylation of Gs alpha, sustained adenylyl cyclase activation, raised cAMP, opening of apical CFTR chloride channels in crypt cells ✓
• C Direct binding to the SGLT1 transporter, blocking coupled glucose-sodium absorption in villous cells
• D ADP-ribosylation of Gi alpha, reduced cAMP, opening of paracellular water channels

Explanation

The B subunit of cholera toxin ADP-ribosylates the stimulatory G protein alpha subunit, locking it in the GTP-bound state. Adenylyl cyclase stays activated, cAMP rises persistently, and crypt cells secrete chloride through apical CFTR channels; sodium and water follow passively, overwhelming absorptive capacity. SGLT1-mediated glucose-sodium uptake is spared, which is precisely why oral rehydration solution works, eliminating option C.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.