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Cell Sensors That Warn Us about Danger

Since their discovery, TRP channels have clarified a mysterious mechanism of human bodies that was not previously known to us. Let's start with the secret of the TRP channels as temperature sensors that warn us about danger.
Illustration: Emi Ozaki

A long-time mystery: Why do human beings feel hot or cold?

We feel "hot" or "cold" using our five senses? You may have such a vague idea. This is not true. We detect a temperature by using the TRP channel family of "cell sensors."
It was discovered in 1997, some 20 years ago. Until then, we did not know for a long time how we felt hot and cold, though human beings, animals and all other living beings on the earth have adapted themselves to their environment. The mystery of temperature sensing was solved by the TRP channel family, which was the discovery of the century*1.

TRP channels are located in cells across the body and send information about "external enemies" and "changes" to the brain. There are 27 kinds of TRP channels, each with a different role. Eleven temperature-sensitive TRP channels include TRPV1, which detects a high temperature of 43℃ or more, and TRPM8, which detects a low temperature of about 26℃ or less.

Illustration: Emi Ozaki

Our body cannot detect danger without TRP channels

The TRP channels are cell receptors that detect a temperature and send signals of "heat" or "cold" to the brain. Detecting "heat," TRPV1 directs sweating to lower the body temperature. We take some action, for example, taking off a jacket. Detecting "cold," TRPM8 makes blood vessels constrict to help conserve body heat. We warm the body by putting on a jacket. In the Aesop's Fables, "The North Wind and the Sun," the sun is stronger than the north wind, because the sun is successful in activating TRPV1, instead of TRPM8.

If our body did not have TRP channels, what would happen? Suppose you go to the Antarctic Continent. You would not feel "cold." You might wear a T-shirt and shorts and walk in bare feet only to get frostbite. If you did not feel "hot," you might bathe in boiling water only to get burnt. Without the temperature-sensitive TRP channels, we would always be exposed to danger.
We feel "pain" touching something extremely hot or cold, which tells us a possible danger. By giving us "pain," the TRP channels protect our body from changes or dangers in the environment.

*1 TRPV1 was discovered as temperature-sensitive receptor by a research group of Doctor David Julius, Professor at the University of California and Doctor Makoto Tominaga (Professor, (present) Exploratory Research Center on Life and Living Systems, National Institute of Natural Sciences) in 1997.

Independent research: Feel the TRP channels (1)

Pour a few drops of peppermint oil in a bathtub before taking a bath on a hot day! Why does bathtub water feel cooler than usual?

Answer: Menthol activates TRPM8 to trick your brain into feeling cooler.

The reason why you feel cool and refreshed in a bathtub or sense that bathtub water is cooler than usual is because menthol activates TRPM8 to send signals of cold to the brain. While feeling cool and refreshed after taking a bath, you can benefit from bathing, including warming the body. Try it!

Why do you feel cool?