Receptors and signaling for sour and salty: the ionic taste qualities.

This review focuses on the cellular and molecular mechanisms underlying sour and salty taste perception in mammals, emphasizing the roles of specific ion channels and taste cell types. Sour taste is mediated exclusively by type III taste cells through the proton-selective channel OTOP1, which allows protons to enter and depolarize the cell, with the inward-rectifying potassium channel Kir2.1 amplifying this response; type III cells then release serotonin to activate afferent nerves. Appetitive salt taste at low sodium concentrations is transduced by a subset of type II taste cells expressing the amiloride-sensitive epithelial sodium channel (ENaC), which depolarizes cells and triggers ATP release via CALHM1/3 channels to stimulate gustatory nerves. Aversive high salt taste involves both type II and type III cells, but the primary depolarizing receptor remains unidentified; however, the chloride channel TMC4 contributes to repolarization of taste cells during high salt stimulation. The review highlights unresolved questions regarding the molecular identity of detectors for amiloride-insensitive salts and the precise contributions of taste cell types in salt taste transduction.