Sweet, salty, sour, bitter, umami.. And now a 6th taste discovered!

We all are familiar with the taste of sweet, salty, sour, bitter, and umami. But In a surprising twist in the world of taste sensations, researchers have unveiled a previously unknown taste and the mechanism behind its detection. The researchers identified the role of a proton-selective ion channel known as OTOP1. This channel, found in our sour taste receptor cells, has been identified as the key player in how we detect ammonium chloride (NH4Cl), the chemical responsible for the unique taste of ammonium.

Ammonium, a breakdown product of amino acids, can be toxic in high quantities, and its detection is essential for the survival of various organisms, from tiny nematode worms to humans. While ammonium's taste has long been the subject of scientific curiosity, its underlying mechanisms have remained elusive.

In a groundbreaking study, scientists have uncovered the remarkable connection between OTOP1 and our ability to taste ammonium chloride. When exposed to extracellular NH4Cl, this proton-selective ion channel triggers significant inward currents in cells. These currents are not only dose-dependent but also correlated with the channel's ability to alkalinize the cell cytosol—a critical aspect of the tasting process.

To validate their findings, the team conducted experiments on Type III taste receptor cells and gustatory nerves. The results were nothing short of astonishing—taste responses to NH4Cl were significantly dampened or even completely eliminated in mice lacking the OTOP1 gene (Otop1−/−). Furthermore, behavioral aversion to NH4Cl, a response observed in mice, was notably diminished in mice without Type II taste receptor cells (Skn-1a−/−).

Reference: “The proton channel OTOP1 is a sensor for the taste of ammonium chloride” by Ziyu Liang, Courtney E. Wilson, Bochuan Teng, Sue C. Kinnamon and Emily R. Liman, 5 October 2023, Nature Communications. DOI: 10.1038/s41467-023-41637-4