Heat-labile enterotoxin is a type of labile

Lability

Lability refers to something that is constantly undergoing change or something that is likely to undergo change.-Chemistry:The term is used to describe a relatively unstable and transient chemical species...

 toxin found in Escherichia coli

Escherichia coli

Escherichia coli is a Gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms . Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans, and are occasionally responsible for product recalls...

 that is inactivated at high temperatures.

It acts similarly to the cholera toxin

Cholera toxin

Cholera toxin is a protein complex secreted by the bacterium Vibrio cholerae. CTX is responsible for the massive, watery diarrhea characteristic of cholera infection.- Structure :...

 by raising cAMP levels through ADP-ribosylation

ADP-ribosylation

ADP-ribosylation is the addition of one or more ADP-ribose moieties to a protein. These reactions are involved in cell signaling and the control of many cell processes, including DNA repair and apoptosis.-ADP-ribosylation enzymes:...

 of the alpha-subunit of a Gs protein leading to the constitutive activation of adenylate cyclase

Adenylate cyclase

Adenylate cyclase is part of the G protein signalling cascade, which transmits chemical signals from outside the cell across the membrane to the inside of the cell ....

. Elevated cAMP levels stimulate secretion of Chloride

Chloride

The chloride ion is formed when the element chlorine, a halogen, picks up one electron to form an anion Cl−. The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides. The chloride ion, and its salts such as sodium chloride, are very soluble in water...

 ions and water from the enterocyte

Enterocyte

Enterocytes, or intestinal absorptive cells, are simple columnar epithelial cells found in the small intestines and colon. A glycocalyx surface coat contains digestive enzymes. Microvilli on the apical surface increase surface area for the digestion and transport of molecules from the intestinal...

 into the gut lumen

Lumen (anatomy)

A lumen in biology is the inside space of a tubular structure, such as an artery or intestine...

, thus causing watery diarrhea

Diarrhea

Diarrhea , also spelled diarrhoea, is the condition of having three or more loose or liquid bowel movements per day. It is a common cause of death in developing countries and the second most common cause of infant deaths worldwide. The loss of fluids through diarrhea can cause dehydration and...

.

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.