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Hyposmolarity‐induced taurine release in cerebellar granule cells is associated with diffusion and not with high‐affinity transport
Author(s) -
Schousboe A.,
Olea R. Sánchez,
Morán J.,
PasantesMorales H.
Publication year - 1991
Publication title -
journal of neuroscience research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.72
H-Index - 160
eISSN - 1097-4547
pISSN - 0360-4012
DOI - 10.1002/jnr.490300409
Subject(s) - taurine , dids , chemistry , biophysics , efflux , osmotic concentration , granule (geology) , divalent , biochemistry , biology , amino acid , membrane , paleontology , organic chemistry
Abstract 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 ++ (5mM) inhibited by 25% and 41%, respectively, the release of taurine observed in 30% hyposmolar media. DIDS (100 μM) inhibited this release by 46%. Taurine efflux 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 high‐affinity carrier‐mediated component plus a nonsaturable diffusion component. The kinetic constants (K m and V max ) 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 × 10 −4 in isosmotic media to 4.6 × 10 −4 ml × min −1 mg −1 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 μM DIDS or 5 mM Mn ++ . 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.