Final answer:
The cholera toxin, produced by Vibrio cholerae, disrupts intestinal cell function and increases cAMP levels, leading to an alkaline environment in the intestinal lumen due to secretion of electrolytes and water.
Step-by-step explanation:
The cholera toxin, an AB exotoxin, creates an alkaline environment in the intestinal lumen when compared to the cytoplasm of the intestinal cells. Cholera toxin is an enterotoxin produced by the gram-negative bacterium Vibrio cholerae. The B subunits of the toxin bind to receptors on the intestinal cells and after entry, the A subunit activates adenyl cyclase, leading to an increased concentration of cyclic AMP (cAMP). This increase in cAMP levels causes the cells to secrete electrolytes and water into the lumen, creating an alkaline environment due to the outflow of chloride ions and accompanying water. This mechanism is responsible for the severe 'rice-water stool' diarrhea that is characteristic of cholera.