Hyposmolarity-induced taurine release in cerebellar granule cells is associated with diffusion and not with high-affinity transport
✍ Scribed by A. Schousboe; R. Sánchez Olea; J. Morán; Dr. H. Pasantes-Morales
- Publisher
- John Wiley and Sons
- Year
- 1991
- Tongue
- English
- Weight
- 532 KB
- Volume
- 30
- Category
- Article
- ISSN
- 0360-4012
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✦ Synopsis
The effects of hyposmotic conditions on taurine uptake and release were studied in mice cultured cerebellar granule cells. The effect of DIDS (4,4'diisothiocyanatostilbene-2,2'-disulfonate) and of the divalent cations Mg+ + and Mn+ + on the hyposmolarity-induced changes in these parameters was investigated. Mg+ + (20 mM) and Mn+ + (5 mM) inhibited by 25 % and 41 % , respectively, the release of taurine observed in 30% hyposmolar media. DIDS (100 pM) inhibited this release by 46%. Taurine eMux evoked by 50% hyposmolar solutions was reduced about 40% by Mg+ + and 55% by Mn+ +. Taurine uptake into the granule cells could be resolved into a highaffinity carrier-mediated component plus a nonsaturable diffusion component. The kinetic constants (K, and V,,,) for the high-affinity uptake were unaffected by a 50% decrease in the osmolarity. The diffusion constant for the nonsaturable taurine uptake was increased from 1.5 X in isosmotic media to 4.6 x ml X min-' X mg-' in hyposmotic (50%) media. This increase in the diffusional component of taurine uptake elicited by the hyposmotic condition was inhibited approximately 25% by either 100 pM DIDS or 5 mM M n + + . These results strongly suggest that the increase in taurine release induced by swelling under hyposmotic conditions is mediated by a diffusional process and not by a reversal of the high-affinity taurine carrier.