U.S., German scientists find sixth taste besides "sweet, bitter and salty": "water taste"

Original title: U.S. and German scientists found in addition to "sweet and bitter salty fresh" the sixth taste: "water taste"
water in the end has no taste? This problem has plagued philosophers and scientists for thousands of years. A conventional view is that taste buds can distinguish between salty, sour, sweet, bitter, fresh tastes, while water is the benchmark of taste, like zero points in coordinates, tasteless. But scientists from the United States and Germany have come up with a new answer: Water does have a "taste" that can be identified by mammalian "sour" taste cells.
May 29, local time, researchers at the California Institute of Technology and the University of Essen in Duisburg, Germany, published a paper, "Mammal taste systems find the cellular mechanisms of water." They experimented with genetic knock-out techniques and photogenetic tools to prove that taste buds, previously thought to be responsible for feeling acid, also have the function of feeling "watery".
past, it was generally accepted that water was the zero point of taste, just as darkness was the zero point of vision. However, many people will have this experience in life: after eating sour food or savoury food immediately drink water, will feel that the water is a little sweet. Therefore, there is also a view that the taste of water is the "aftertaste" of food.
modern science has shown that insects and amphibians can taste water. Fruit flies, for example, can sense the taste of water by connecting the hair of their wings, thighs and kisses to a group of neurons. Mammals also have similar neurons. Brain imaging shows that there is an area of the cerebral cortical that reacts specificly to water.
, how does water feel in the mouth? What neural paths do the perceived signals pass to the brain? Scientists know almost nothing. Such neural paths should exist because animals know to drink enough water before blood and internal organs detect water replenishment, thus stopping drinking water.
team found the starting point for this neural path, the taste receptor that senses the "smell of water." It is well known that those small protrusions that are dense on the tongue are taste receptors, taste buds, which contain taste cells. Previously, people only knew that they could perceive salty, sour, sweet, bitter, fresh five basic flavors, which taste buds can perceive "water taste"? The researchers used genetic knocks to "silence" different taste cells in mice, even if they could not sense the taste they could otherwise perceive, and then filled the rat's mouth with water to see how the cells reacted. Experiments have shown that "sour" taste cells become unusually active when exposed to water.
addition, "sour" taste cells are silenced by mice, which take longer to distinguish between water and a colorless, odorless silicone oil.
to further test the role of acid-flavored cells in the perception of "water-smelling" neural pathps, the researchers used optogenetics tools. Photogenetics tools have been a star technology in biology in recent years, with the core content of implanting a special plant gene into the organism that reacts differently to different bands of light to express the proteins researchers need. This time, the researchers set out that a blue light activates "sour" taste cells to express specific proteins.
sure enough, the mice, which had been cut off for two days by the researchers, began licking the blue light source and acting as if they had drunk water. This "drink-up" behavior was persistent, with some thirsty mice "drinking" 2,000 mouthfuls in 10 minutes. This confirms that "sour" taste cells are indeed sensors that provide a "drink to water" signal, and on the other hand suggests that "sour" taste cells do not provide a signal to "drink enough water".
Yuki Oka of the California Institute of Technology, one of the authors of the study, speculates that water dilutes saliva and alters the acidity and alkalinity of saliva, activating "acidic" taste cells.