THE DIVERSITY OF VOLUME REGULATORY MECHANISMS

Mammalian cells utilize a wide variety of cell volume regulatory mecha nisms. For rapid adjustment of cell volume cells release or accumulate ions through respective channels and transport systems across the cel l membrane. The most widely used mechanisms of cell volume regulatory ion release include ion channels and KCI symport. Ion uptake is most f requently mediated by Na+ channels, Na+, K+, 2Cl(-) cotransport, and N a+/H+ exchange. Chronic adjustment of cell osmolarity is accomplished by the formation or accumulation of organic osmolytes, molecules speci fically designed to create intracellular osmolarity without interferin g with cellular function. The most widely occurring osmolytes are sorb itol, inositol, glycerophosphorylcholine, betaine, taurine, and amino acids. The osmolytes are either synthesized by or transported into shr unken cells. During cell swelling osmolytes can be rapidly degraded or released. Any given cell may utilize several volume-regulatory mechan isms. Moreover, different mechanisms are utilized in different tissues . The diversity of cell volume regulatory mechanisms allows the cells to defend the constancy of cell volume against a myriad of challenges with relatively little impairment of cellular function.