HYPOTONICITY-EVOKED RELEASE OF ORGANIC OSMOLYTES FROM DISTAL RENAL-CELLS - SYSTEMS, SIGNALS, AND SIDEDNESS

After a detailed description of early cellular, membrane and intracell ular events in rat renal medullary collecting duct cells when exposed to hypotonicity, a synopsis on organic osmolyte transport properties, possible trigger mechanisms, and the cellular location of transport pa thways is given. From the data currently available on renal and nonren al cells, it is concluded that hypotonicity-evoked efflux of all organ ic osmolytes appears to be mediated by transport proteins which share a variety of properties more typical for channels than for carriers. A large diversity seems to exist, however, for the signalling mechanism s. Such diversity allows the cells to regulate the intracellular conce ntration of different organic osmolytes independently of each other, g iving flexibility to the spectrum of osmotic responses. The site of re lease also varies from cell to cell; here conservation of organic osmo lytes for future reuptake or further metabolism appears to be the majo r determinant.