Taste, as one of the most fundamental animal sensations, enables animals to select for appetitive food that normally contains nutrients and to avoid potentially toxic or rotten food. Among sweet, bitter, umami, salty and sour, the basic five mammalian taste modalities, sour is the least understood currently with its primary receptor not being identified. Sour taste is usually triggered by acids, which when dissolved are able to release protons. It has been discovered that an apically-localized proton current drives the action potential firing in dissociated sour taste cells that may mediate the acid sensation, but very little is known about its distribution and biophysical properties. Here in my research, I found that the proton current is present in sour taste cells isolated from all taste fields, but absent in non-sour taste cells, which confirms its specificity in sour taste. Meanwhile, the biophysical properties such as the inward rectification, the pH-dependence of Zn 2+ sensitivity, and the opening at very mild acidic pH may provide clues for the molecular identification of this channel.