GI physiology: cholera toxin: practice question

A Physiology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Physiology · GI physiology: cholera toxin

Sample item

In cholera the enterocyte secretes large volumes of chloride-rich fluid. Which sequence correctly describes the molecular action of the toxin?

ACleavage of tight junction proteins, causing paracellular leakBADP-ribosylation of Gi protein, lowering cAMP and closing chloride channelsCInhibition of the sodium-potassium pump, causing cell swellingDADP-ribosylation of Gs protein, raising cAMP and opening the CFTR chloride channel

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. ADP-ribosylation of Gs protein, raising cAMP and opening the CFTR chloride channel

Vibrio cholerae toxin ADP-ribosylates the alpha subunit of the Gs protein so that adenylyl cyclase is permanently active. The resulting rise in cAMP activates protein kinase A, which opens CFTR chloride channels in the crypt cell apical membrane. Chloride, sodium and water are secreted into the lumen, causing rice-water stools.

Option by option

A. Cleavage of tight junction proteins, causing paracellular leak
Tight junction cleavage is not the main mechanism of cholera toxin; it acts through the cell's second messenger.
B. ADP-ribosylation of Gi protein, lowering cAMP and closing chloride channels
ADP-ribosylation of Gi is the action of pertussis toxin and it does not apply to cholera.
C. Inhibition of the sodium-potassium pump, causing cell swelling
Na/K pump inhibition is not the action of the toxin, and secretion is cAMP-driven.
D. ADP-ribosylation of Gs protein, raising cAMP and opening the CFTR chloride channel (correct)
Permanent Gs activation raises cAMP and opens CFTR.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is D, ADP-ribosylation of Gs protein, raising cAMP and opening the CFTR chloride channel. Vibrio cholerae toxin ADP-ribosylates the alpha subunit of the Gs protein so that adenylyl cyclase is permanently active.

Why is "Cleavage of tight junction proteins, causing paracellular leak" not the answer?

Tight junction cleavage is not the main mechanism of cholera toxin; it acts through the cell's second messenger.

Why is "ADP-ribosylation of Gi protein, lowering cAMP and closing chloride ch…" not the answer?

ADP-ribosylation of Gi is the action of pertussis toxin and it does not apply to cholera.

Why is "Inhibition of the sodium-potassium pump, causing cell swelling" not the answer?

Na/K pump inhibition is not the action of the toxin, and secretion is cAMP-driven.

What concept does this question test?

It tests GI physiology: cholera toxin in Physiology. The resulting rise in cAMP activates protein kinase A, which opens CFTR chloride channels in the crypt cell apical membrane. Chloride, sodium and water are secreted into the lumen, causing rice-water stools.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study GI physiology: cholera toxin?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.