Question

Which intestinal membrane transporter is exploited in the therapeutic management (oral rehydration) of secretory diarrhea?

• A. CFTR chloride channel
• B. SGLT (sodium-glucose cotransporter)
• C. Na\(^+\)/K\(^+\) ATPase pump
• D. Aquaporin-2 water channel

Hint:

Why does ORS contain both salt AND glucose? The cotransporter that links them is the answer.

Answer 1

The Correct Option is B

Step 1: Understand the basis of oral rehydration therapy (ORT).
In secretory diarrhea (e.g. cholera), the toxin activates the CFTR chloride channel, driving massive secretion of Cl\(^-\), Na\(^+\) and water into the gut lumen. CFTR is the culprit, not the therapeutic target.

Step 2: Identify the channel used for treatment.
The cornerstone of treatment is oral rehydration solution (ORS), which works through the sodium-glucose cotransporter, SGLT1, in the brush border of enterocytes. SGLT1 absorbs Na\(^+\) coupled to glucose, and water follows osmotically.

Step 3: Why SGLT is the answer.
Crucially, SGLT1-mediated Na\(^+-glucose absorption remains intact even when cholera toxin is active. By supplying glucose and sodium together, ORS harnesses this surviving pathway to reabsorb Na\(^+\) and water, reversing dehydration. This coupling is the physiological rationale for adding glucose to ORS.

Step 4: Why the others are wrong.
• CFTR - mediates the secretion causing the diarrhea; we do not use it to treat.
• Na\(^+\)/K\(^+\) ATPase - a basolateral pump that maintains the Na\(^+\) gradient, but it is not the directly exploited luminal absorptive route in ORS.
• Aquaporin-2 - an ADH-regulated water channel in the renal collecting duct, irrelevant to intestinal ORT.

Key fact: ORS works by SGLT1-mediated Na\(^+\)-glucose coupled absorption, which stays functional in secretory diarrhea.