HomeScience and ResearchAnimal StudiesNew Taste Receptor Identified Helps Fruit Flies Avoid Alkaline Food

New Taste Receptor Identified Helps Fruit Flies Avoid Alkaline Food

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How do flies detect the taste of alkaline?

While taste is one of the first senses that come into contact with food, it has been unclear until now whether animals can taste alkaline substances and how they do it.

The Monell Chemical Senses Center team has uncovered the molecular mechanism behind the perception of alkaline taste. Through their study on fruit flies, they have shed light on how various species can recognize and avoid high-pH or alkaline foods.

Led by Yali Zhang, PhD, the researchers have identified a new taste receptor called alkaliphile (Alka), which is a chloride ion channel that responds to alkaline pH. The team’s findings were published in Nature Metabolism and highlighted in Nature.

This study is a continuation of their previous work on sour taste at the lower end of the pH scale in 2021.

The acidity or basicity of a substance, measured on the pH scale, is crucial for biological processes such as enzyme reactions and food digestion. The pH level must be appropriately balanced for these processes to occur. While we are familiar with sour taste, which corresponds to acidic substances and enables us to detect the low end of the pH scale, little is known about how animals perceive the opposite end of the pH spectrum associated with basic substances. Detecting both acids and bases, which are commonly found in food sources, is important as they can significantly affect the nutritional value of what animals consume.

According to Zhang’s team, the Alka taste receptor is present in the gustatory receptor neurons (GRNs) of fruit flies, which are similar to taste receptor cells in mammals. When presented with neutral or alkaline food options, wild-type fruit flies typically choose neutral foods due to the toxicity of high pH. However, when Alka is absent, the flies lose the ability to distinguish between alkaline and neutral foods. In humans, ingesting food with a high pH level can be harmful, leading to health issues such as muscle spasms, nausea, and numbness. Similarly, after consuming high-pH foods, fruit flies’ lifespan can be shortened.

The research team’s findings reveal that Alka plays a crucial role in enabling fruit flies to avoid potentially dangerous alkaline environments.

“Detecting the alkaline pH of food is an advantageous adaptation that helps animals avoid consuming toxic substances,” adds Zhang.

Zhang’s team conducted electrophysiological tests to better understand how Alka responds to high pH and discovered that Alka produces a chloride ion (Cl-) channel that is instantly activated by hydroxide ions (OH-). The concentration of Cl- within the fly’s GRN is normally greater than outside the nerve cell, similar to olfactory sensory neurons in humans. According to Zhang, when the fly is subjected to high-pH stimuli, the Alka channel opens, allowing negatively charged Cl- to flow from the fly’s GRN to the outside. The fly brain receives a signal that the meal is alkaline and should be avoided as a result of this outflow of Cl-, which activates the GRN.

This “work shows that Cl- and Cl- channels, which have been overlooked for a long time, have crucial functions in taste signaling to the brain,” adds Zhang.

Also, Zhang’s team used light-based optogenetic methods to investigate how flies recognize the taste of alkaline compounds. They discovered that the flies were no longer affected by the flavor of alkaline food when they switched off the alkaline GRNs. Conversely, they activated these alkaline GRNs by shining red light on them. It’s interesting to note that when these flies were simultaneously fed sweet food and exposed to red light, they no longer want to consume the sweet food. 

“Alkaline taste can make a big impact on what flies choose to eat,” remarks Zhang.

Over all, Zhang’s team has determined that Alka is a novel taste receptor specifically tuned to detect the alkaline pH of food. His team plans to investigate if animals have similar high-pH detectors in the future. 

“Our work has settled the argument about whether there is a taste for alkaline things,” adds Zhang. “There definitely is.”

Research on new tastes of animals, including humans, can help us learn more about eating habits and come up with ways to improve nutrition.

The Ambrose Monell Fund and the National Institute on Deafness and Other Communication Disorders provided funding for this study.

Image Credit: Yali Zhang, Monell Chemical Senses Center

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