Heat-Labile Enterotoxin

Heat-labile enterotoxin is a type of labile toxin found in Escherichia coli and Bacillus cereus. The heat-labile enterotoxin is inactivated at high temperatures. It acts similarly to the cholera toxin by raising cAMP levels through ADP-ribosylation of the alpha-subunit of a Gs protein leading to the constitutive activation of adenylate cyclase. Elevated cAMP levels stimulate the activation of the CFTR channel thus stimulating secretion of chloride ions and water from the enterocyte into the gut lumen. This ionic imbalance causes watery diarrhea. In addition to its effects on chloride secretion, which involve the same steps as the effects of cholera toxin, heat-labile enterotoxin binds additional substrates: lipopolysaccharide on the surface of E. coli cells and A-type blood antigens. The importance of these binding events is not yet known.