Role of taurine in neural cell volume regulation

Release of taurine and other amino acids was monitored from cultured astrocytes and neurons under isosmotic and hyposmotic conditions as well as during exposure of the cells to 56 mM KCl. The release was correlated with swelling, as determined by the 3-O-methylglucose method. It was shown that release of taurine from astrocytes cultured from cerebral cortex and cerebellum of rats and mice regardless of the stimulating agent is a consequence of cell swelling. The release is unrelated to depolarization. This conclusion is also valid regarding release of taurine from cerebellar granule neurons. Comparison of release of different amino acids showed that not only taurine but also to some extent glutamate, aspartate, and glycine are released during cell swelling. On the other hand, glutamine is not released under these conditions. Studies of uptake of taurine under isosmotic and hyposmotic conditions as well as the dependency of the release on sodium and temperature strongly suggest that the release process is mediated by diffusional forces and not by a reversal of the high-affinity carrier. It is proposed that taurine may play an important role as an osmotically active substance in the brain involved in cell volume regulation.