CELLULAR AND MOLECULAR PHYSIOLOGY OF VOLUME-SENSITIVE ANION CHANNELS

Maintenance of a constant cell volume in the face of osmotic stress is an evolutionarily ancient homeostatic process. Over the last two deca des physiologists have gained an impressive understanding of the ''vol ume-sensitive'' channels, cotransporters, exchangers, metabolic pathwa ys, and genes that are responsible for modulating intracellular solute content and cell volume. This review focuses on one part of this stor y, the characteristics and osmoregulatory functions of volume-sensitiv e anion channels. Three distinct types of swelling-activated anion cha nnels have been observed and studied extensively in animal cells. Thes e channels include 1) CIC-2, which is a member of the CIC family of vo ltage-gated anion channels, 2) an outwardly rectifying intermediate co nductance channel, and 3) a large-conductance or ''maxi'' channel. In addition to these three channels, several other less well-characterize d anion channels have been observed. This review discusses the electro physiological and molecular biological characteristics and regulation of these channels. The possible roles different types of anion channel s might play in cell volume homeostasis are also discussed.