The functions and roles of the extracellular Ca2+-sensing receptor along the gastrointestinal tract.

Digestion of food and normal salt and water homeostasis in the body require a functional digestive tract. Recently an increasing number of studies have demonstrated a role for the calcium-sensing receptor along the entire gastrointestinal tract and its role in normal gut physiology. Detailed studies have been performed on colonic fluid transport and gastric acid secretion. We have now demonstrated that the receptor can modulate fluid secretion and absorption along the intestine and can thereby be a potent target to prevent secretory diarrhea. Recent studies have demonstrated that organic nutrients such as polyamines and l-amino acids can act as agonists by allosterically modifying the receptor. Thus, the receptor may detect nutrient availability to epithelial cells along the gastrointestinal tract and may be involved in the coordinated rapid turnover of the intestinal epithelium. Furthermore, the receptor has been suggested as a link for the mechanisms leading to calcium uptake by the colon and may thus reduce the risk for colon cancer.