The balance of fluid and ions in the internal environment of the body is a prerequisite for mammalian homeostasis. Certain microbial enterotoxins, in particular the cholera toxin produced by Vibrio cholera, can disrupt this balance. Consideration of the molecular mechanisms of secretory diarrhea seems appropriate for several reasons:(i) this disease continues to have a significant impact on societies across many countries and continents (Butler, 2017), (ii) the pathomechanism involving the transcellular and paracellular pathways is cruicial for understanding the effect of cholera toxin on the redistribution of ions and water, and (iii) these mechanisms lay the foundation for further development of preventive and therapeutic strategies.
When discussing the contribution of paracellular pathway to secretory diarrhea induced by cholera toxin, two key aspects should be considered. First, net ion secretion into the intestinal lumen results from the balance between two processes: the absorption of ions from the chyme into the intercellular fluid and the secretion in the opposite direction during cholera toxin activity. While oral administration of rehydration solutions allows to effectively restore the volume of the internal environment of the body, they do not reduce the volume of stool (Butler, 2017), highlighting the molecular independence of these processes. Second, chloride and sodium ions cannot be considered as separate counterions, as their diffusion occurs in an equimolar ratio, driven by both concentration and electrical gradients.