NEW YORK - German researchers have isolated the cellular structures--known as receptors--that enable the tongue to detect certain, potentially deadly bitter-tasting substances.

Apparently, humans have the family of TAS2R receptors to thank for telling us when particular bitter compounds are in our mouths--an ability that lets us detect when we are mistakenly ingesting toxic substances.

Study author Dr. Wolfgang Meyerhof of the German Institute of Human Nutrition in Potsdam-Rehbrucke told Reuters Health that the particular receptors isolated in the study help tongues pick out amygdalin, a component of bitter almonds. Unlike the sweet almonds available in supermarkets, bitter almonds contain traces of a toxic substance when raw. Although cooking destroys the toxin, the nuts are illegal in the US.

"Five bitter almonds are said to kill a child," Meyerhof remarked.

Identifying the body processes that enable taste perception is important for other reasons, as well: taste also has a strong influence on food choices and the amount of food we eat, Meyerhof said, and a good, flavorful meal can have a very strong effect on your mood.

"Understanding taste may in the long term help to fight obesity," Meyerhof noted. "Loss of taste is loss of weight."

Meyerhof and his colleagues report their findings in the online advance edition of the journal Nature Genetics.

The researchers discovered the receptors by scanning human genetic material for a DNA sequence that matched genes that are believed to encode for receptors in the tongues of rats. They discovered that humans have genetic material that encodes for the group of receptors called TAS2R, which detect bitter substances.

In an interview, Meyerhof explained that the TAS2R receptors are located on the surface of taste receptor cells, where they bind to and are activated by bitter compounds. This results in biochemical reactions inside the cells that lead to the release of chemicals that excite nerves, ultimately sending nerve impulses from the tongue to the brain.

For example, receptor TAS2R16 detects salicin, a substance present in willow bark that has been used for more than 3,000 years to reduce pain and fever, Meyerhof noted. A new version of the treatment is called acetylsalicylic acid--otherwise known as aspirin.

People who lack this group of receptors would be unable to taste salicin or amygdalin, as well as the other bitter substances that activate the TAS2R receptors, the researcher added.

SOURCE: Nature Genetics 15 October 2002;doi;10.1038/ng1014.