Scientists have discovered that the tongue can detect ammonium chloride as a sixth primary taste.
In addition, the tongue senses sweet, sour, salty, bitter and other basic tastes.
Research published Thursday in the journal Nature Communications shows that protein receptors on the tongue that help detect sour tastes also sense the taste of ammonium chloride, a popular ingredient in Scandinavian candies.
“If you live in a Scandinavian country, you’re familiar with the flavor and probably like it,” says Emily Lemon, a neuroscientist at the University of Southern California and co-author of the study. ‘
Salt licorice has been a popular candy in some northern European countries since at least the early 20th century and contains salicylic salt or ammonium chloride as an ingredient.
Although scientists know that the tongue responds in some way to tasting ammonium chloride, the specific protein receptors on the tongue that elicit this response have remained elusive despite decades of extensive research.
This situation became clearer when recent research revealed a protein that detects sour taste through a tongue protein receptor called OTOP-1.
This protein is found inside the cell membranes in the tongue and creates a pathway for hydrogen ions. Hydrogen ions are the main component of acidic foods that reach the cells of the tongue through this route.
OTOP One, lemon water is rich in citric and ascorbic acid and plays an important role in other tart drinks such as vinegar. Thus, when such food reaches the tongue, the tongue feels sour.
Since ammonium chloride also affects the concentration of hydrogen ions in the cell, the researchers wondered if it also activates OTOP-1.
To test this, the scientists inserted the gene behind the OTOP1 receptor into lab-grown human cells to make the cells produce the OTOP1 receptor.
The researchers then exposed these cells to acid or ammonium chloride and tested the response.
‘We found that ammonium chloride activates the OTOP-1 channel in a really robust way,’ Dr Lemmon said. It activates it as well or better than acid.’
A small amount of ammonia was found to be transported into the cell from ammonium chloride.
Since ammonia is alkaline, it raises the pH (acid or base concentration) which reduces hydrogen ions.
This pH difference causes hydrogen ions to travel through the OTOP one, which can be detected by measuring changes in electrical conductivity in the channel, the scientists say.
To measure this, the scientists used taste-sensing cells in normal mice and genetically modified mice that do not produce OTOP-1.
They measured how well the taste cells produced electrical responses when ammonium chloride was administered.
The study showed that although OTOP-1 is important for the taste cells of normal mice to respond to salty substances such as ammonium chloride, the taste cells of mice without OTOP-1 were unable to taste salty tastes. The latter failed to send the correct signals to the brain.
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This confirms that OTOP one reacts with ammonium chloride.
The scientists also discovered that mice with an active OTOP-1 protein found the taste of ammonium chloride unattractive and did not drink the salted water. Whereas mice lacking this protein had no objection to high-salt solutions.
According to Dr Lemmon: ‘It was a really big deal. This suggests that the presence of the OTOP one channel is essential for behavioral responses in response to ammonium.’
The researchers also found that the OTOP one channel appears to be more sensitive to ammonium chloride in some species than in others.
The researchers believe that ammonium chloride’s ability to taste may have helped prevent organisms from eating harmful organic matter that was high in ammonium.
“Ammonium is found in the waste material,” explains Dr. Lemon. Consider fertilizers that are somewhat toxic. So it makes sense that our taste system evolved to detect it.’ However, he added that more research is needed to understand the differences between species in this regard.
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