PROPERTIES AND GLIAL ORIGIN OF OSMOTIC-DEPENDENT RELEASE OF TAURINE FROM THE RAT SUPRAOPTIC NUCLEUS

1. Taurine, prominently concentrated in glial cells in tile supraoptic nucleus (SON), is probably involved in the inhibition of SON vasopres sin neurones by peripheral hypotonic stimulus, via activation of neuro nal glycine receptors. We report here the properties and origin of the osmolarity-dependent release of preloaded [H-3]taurine from isolated whole SO nuclei. 2. Hyposmotic medium induced a rapid, reversible and dose-dependent increase in taurine release. Release showed a high sens itivity to osmotic change, with a significant enhancement with less th an a 5 % decrease in osmolarity. Hyperosmotic stimulus decreased basal release. 3. Evoked release was independent of extracellular Ca2+ and Na+, and was blocked by the Cl- channel blockers DIDS (4,4'-diisothioc yanatostilbene-2,2'-disulphonic acid) and DPC (N-phenylanthranilic aci d), suggesting a diffusion process through volume-sensitive Cl- channe ls. 4. Evoked release was transient for large osmotic reductions (grea ter than or equal to 15%), probably reflecting regulatory volume decre ase (RVD). However, it was sustained for smaller changes, suggesting t hat taurine release induced by physiological variations in osmolarity is not linked to RVD. 5. Basal and evoked release were strongly inhibi ted by an incubation of the tissue with the glia-specific toxin fluoro citrate, but were unaffected by a neurotoxic treatment with NMDA, demo nstrating the glial origin of the release of taurine in the SON. 6. Th e high osmosensitivity of taurine release suggests an important role i n the osmoregulation of the SON function. These results strengthen the notion of an implication of taurine and glial cells in the regulation of the whole-body fluid balance through the modulation of vasopressin release.