Researchers Enhance Scientific Understanding of Calcium Taste

Though calcium taste doesn’t fit into the five established tastes the tongue’s receptors can identify, humans describe it as slightly bitter and sour. According to a new study published in the journal Neuron, calcium taste also exists in fruit flies (Drosophila melanogaster).

Lee et al demonstrated that fruit flies are indifferent to low calcium (Ca²⁺) and averse to high levels. Image credit: Peter Allen.

Professor Craig Montell from the University of California, Santa Barbara, and co-authors uncovered a unique class of gustatory receptor neurons (GRNs) necessary for calcium taste in fruit flies.

“Our team wanted to understand the underlying mechanisms used to respond to the presence of calcium in food,” Professor Montell said.

“We not only identified the taste neurons but also found three receptor proteins that are important in sensing calcium.”

“In fact, eliminating any one of them allowed us to do an interesting survival experiment.”

The researchers used Petri dishes with one side containing solely sugar (fructose) and the other a mix of sugar and a high level of calcium.

Normal flies that rejected the high-calcium side and ate only pure fructose survived.

Mutant flies — those in which any one of the three GRNs was removed — were unable to distinguish the two halves of the Petri dish.

As a result, they consumed enough of the calcium to cause viability problems and, over time, died.

“It turns out that fruit flies don’t have a mechanism for sensing low calcium even though it’s good for them, but they are trying to guard against consuming too much calcium,” Professor Montell said.

“Surprisingly, we found that calcium avoidance occurred through two mechanisms: activation of a unique class of GRNs, distinct from those that sense bitter compounds and which cause a stop-feeding signal when activated.”

“In addition, calcium inhibits sugar-activated GRNs.”

“In humans, high calcium is associated with many diseases and can even be life threatening,” he said.

“Our results suggest that calcium taste might function primarily as a deterrent in wide range of animals, including humans.”

_____

Youngseok Lee et al. 2018. Calcium Taste Avoidance in Drosophila. Neuron 97 (1): 67-74; doi: 10.1016/j.neuron.2017.11.038