The five basic tastes are sensed on the tongue by different sets of cells, but the acidic taste of sour has long defied molecular analysis. Now researchers have genetically engineered mice in which they can fluorescently tag sour-taste cells (pictured), and have pinpointed the changes that acid triggers in the cells.

Credit: NATL ACAD. SCI.

Isolating the cellular mechanisms associated with sour-taste recognition has been challenging because many ion channels in cell membranes respond to acid, whether or not they are involved in sour sensing. Emily Liman and her team at the University of Southern California in Los Angeles tagged not only the sour-taste cells but also those for bitter, sweet and umami, and compared the responses of these cells to acid. They found that the sour-taste cells fired alone when protons were transported across the membrane — but all cells reacted to sodium ions, which were previously thought to mediate sour sensing.

Proc. Natl Acad. Sci. USA doi:10.1073/pnas.1013664107 (2010)