New role of taurine as an osmomediator between glial cells and neurons in the rat supraoptic nucleus.

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Taurine has an established function as an osmolyte in the nervous system. Present inside cells at high concentration, it is released upon cell swelling induced by a decrease in extracellular tonicity. The loss of taurine is believed to contribute in a major way to the subsequent regulatory volume decrease (RVD) undergone by both neurons and astrocytes25. However, some observations indicate that the osmoregulatory role of taurine in the nervous system may be more complicated than sometimes thought. First, the distribution of taurine is not homogenous, as it is concentrated in selected sets of cells in various brain areas. For instance, it is found almost exclusively in Purkinje neurons in the cerebellum24, primarily in neurons in hippocampal and cortical formations, but prominently in astrocytes in the hypothalamus and brain stem18,32. While volume regulation of all brain cells should be critical for proper neuronal function, the uneven distribution of taurine suggests a differential use of this amino acid by the various cell populations. Second, taurine is not an inactive compound as it would be expected for an “ideal” osmolyte. Taurine is an agonist of the inhibitory ligand-gated channels glycine and GABAA receptors , binds to the metahtropic GABAB receptor14,17, and alters the electrical activity of neurons and other excitable cells to various extents9,31. Therefore, release of taurine from brain cells under hypotonic stress may well serve other function 4,9,11,36