The sour taste of a proton current

Sour taste can be agreeable in moderation. However, most people respond to drinking lemon juice with a violent contortion of their faces that clearly signals to everybody around that a mouth free of acid is greatly preferred. Such a strong aversive response must be based on a reliable acid-detection system on the tongue. Emily Liman's Laboratory of Sensory Neurobiology at the University of Southern California has discovered that specialized sour-taste cells on the tongue are equipped with proton channels. In PNAS (1), strong evidence is presented for the idea that H+ ions, resulting from the dissociation of food acids, enter sour-specific taste cells that inform the brain about the offensive material. The brain can then decide what to do—often to pull a “sour face.”