Cell Volume Regulation in Taurine Deficient Cultured Astrocytes

Abstract

A large variety of cells are able to regulate their cell volume under anisosmotic conditions. Cell volume regulation involves the activation of fluxes of osmotically active solutes, which have been classified as inorganic ions, Na⁺, K⁺ and Cl⁻, and organic molecules, such as polyols and amino acids. In the nervous system, taurine seems to be the most important organic osmolyte. Cultured astrocytes and neurons regulate cell volume under hyposmotic conditions (6,14). The induced release of taurine parallels this process, suggesting that taurine is involved in the regulatory mechanism (15,18). Moreover, substantial evidence supports a similar role for taurine in brain in vivo. Brain taurine levels decrease subsequent to plasma hyposmolarity during experimental chronic hyponatremia (22). Correspondingly, increases are observed in extracellular taurine concentrations, assessed by dialysis in brain, in response to a number of conditions that induce neural cell swelling such as seizure activity, excitotoxic agents and intracellular acidosis (1,8,9). This association of taurine and cell swelling has been directly demonstrated by showing a significant release of taurine after a direct reduction in the extracellular osmolarity (7). Numerous observations in systems in vitro, including brain slices, synaptosomes, isolated retina and cultured neurons and astrocytes, also document the increased efflux of taurine associated with cell swelling, suggesting its involvement in the processes of cell volume adjustment in nervous tissue (2,12,15,17,18).