The Sixth Sense: An Exploration into How Ammonium Chloride Stimulates the Sour Receptor of the Tongue

Monday - October 9 2023, 07:16 UTC - 1 year ago

This study explores the sixth taste known as ammonium chloride, which activates the protein OTOP1 to stimulate the sour receptor on the tongue. It also modulates behaviour in mice with the OTOP1 receptor. Different species have shown varying levels of sensitivity to the salt, likely due to different dietary habits and ecological niches.

You may have heard of the five basic tastes: sweet, sour, salty, bitter, and umami. But did you know that there is a sixth one? Scientists have discovered that ammonium chloride, a salt used in some Scandinavian candies, can stimulate the same receptor that detects sourness on the tongue. The study, published in Nature Communications on Thursday, reveals how ammonium chloride interacts with a protein called OTOP1, which is responsible for sensing acidic foods like lemonade and vinegar .

The researchers found that ammonium chloride not only activates OTOP1 but also alters the pH inside the taste cells, causing more hydrogen ions to flow through the receptor. The study's lead author, Dr. Emily Liman from the University of Southern California, said that ammonium chloride is a very potent stimulator of OTOP1. "It activates as well or better than acids," she said. "If you live in a Scandinavian country, you will be familiar with and may like this taste .

" Ammonium chloride is the main ingredient of salt licorice, a popular candy in some northern European countries. The salt has a distinctive flavor that some people find pleasant, and others find repulsive. Dr. Liman said she did not like it but was curious about how it affects the taste buds. To investigate this, the researchers used lab-grown human cells that expressed OTOP1 and exposed them to acid or ammonium chloride .

They measured the electrical responses of the cells and found that both stimuli activated OTOP1. They also used mouse taste cells that either had or lacked OTOP1 and gauged their reactions to ammonium chloride. They found that only the cells with OTOP1 responded to the salt, confirming that it is the critical receptor for this taste. The researchers also tested how mice behaved when given water with or without ammonium chloride .

They found that mice with OTOP1 avoided drinking the water with the salt, while mice without OTOP1 did not show any preference. This suggests that OTOP1 is essential for the aversive response to ammonium chloride. Dr. Liman said that this finding was surprising because it shows that OTOP1 is not only involved in detecting sourness but also in modulating the behavior of animals. She said this may have been an evolutionary adaptation to help animals avoid eating harmful substances containing high ammonium levels .

The researchers also found that different species have different sensitivities to ammonium chloride. They compared the responses of human, mouse, and frog cells and found that frog cells were more sensitive than human and mouse cells. Dr. Liman said that this may reflect these animals' different dietary habits and ecological niches. The study sheds new light on how taste works and influences our food choices .

It also opens up new possibilities for exploring other tastes beyond the six basic ones.