Chloride Channels: Often Enigmatic, Rarely Predictable

Until recently, anion (Cl-) channels have received considerably less attention than cation channels. One reason for this may be that many Cl- channels perform functions that might be considered cell-biological, like fluid secretion and cell volume regulation, whereas cation channels have historically been associated with cellular excitability, which typically happens more rapidly. In this review, we discuss the recent explosion of interest in Cl- channels, with special emphasis on new and often surprising developments over the past five years. This is exemplified by the findings that more than half of the ClC family members are antiporters, and not channels, as was previously thought, and that bestrophins, previously prime candidates for Ca2+-activated Cl- channels, have been supplanted by the newly discovered anoctamins and now hold a tenuous position in the Cl- channel world.