Monell Chemical Senses Center researcher Yali Zhang and colleagues identified a previously unknown chloride ion channel, which they named alkaliphile (Alka), as a taste receptor for alkaline pH.
pH, the scale of how acidic or basic a substance is, plays an essential role for living organisms because many biological processes, such as breaking down food and enzymatic reactions, need the level of pH to be just right.
While we are familiar with sour taste, which is associated with acids and allows us to sense the acidic end of the pH scale, little is known about how animals perceive bases on the opposite end of the pH spectrum.
Detecting both acids and bases, which are commonly present in food sources, is important because they can significantly impact the nutritional properties of what animals consume.
Dr. Zhang and co-authors found that Alka is expressed in the gustatory receptor neurons (GRNs) of the fruit fly (Drosophila melanogaster) — the counterpart of taste receptor cells of mammals.
When facing neutral food versus alkaline food, wild-type flies normally choose neutral foods because of the toxicity of high pH.
In contrast, flies lacking Alka lose the ability to discriminate against alkaline food when presented with it.
If the pH of a food is too high, in humans it can be harmful and cause health concerns such as muscle spasms, nausea, and numbness.
Likewise, after fruit flies eat food with high pH, their lifespan can be shortened.
The authors demonstrated that Alka is critical for flies to stay away from harmful alkaline environments.
“Detecting the alkaline pH of food is an advantageous adaptation that helps animals avoid consuming toxic substances,” Dr. Zhang said.
To understand how Alka senses high pH, the team performed electrophysiological analyses and found that Alka forms a chloride ion (Cl–) channel that is directly activated by hydroxide ions (OH–).
Like olfactory sensory neurons in mammals, the concentration of Cl– inside the…
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