Exposure of cells to acidic conditions outside the cell activates chloride-conducting channels that influence physiological and pathological processes. Yang et al. used an unbiased RNA interference screen to identify the channel protein that allows such proton-activated ion conductance. The protein, called PAC for proton-activated channel, has two predicted transmembrane domains and is unlike any previously identified channel. Identification of the channel should advance studies of its physiological roles, which range from tissue injury after stroke to adaptation of Tibetan natives to a high-altitude environment.
