Dose-dependent, K+-stimulated efflux of endogenous taurine from primary astrocyte cultures is Ca2+-dependent.
The K+-stimulated efflux of endogenous taurine from primary rat cerebellar astrocyte cultures prepared from 7-9-day-old rats was studied at 16-18 days in vitro using HPLC analysis. Taurine efflux was dose-dependent at K+ concentrations between 10 mM and 80 mM, with an EC50 of approximately 50 mM. Maximum stimulation of efflux above basal levels ranged from 56% at 10 mM K+ (204 pmol/min/mg protein) to 470% at 80 mM K+ (960 pmol/min/mg protein). Removal of Ca2+ from the buffer and the addition of either 1 mM EGTA or 10 mM Mg2+ abolished K+-stimulated efflux. Taurine efflux peaked and fell in parallel with the K+ concentration, but with an approximate lag of 3-5 min. The time course and amount of preloaded [3H]taurine released did not differ significantly from that seen for endogenous efflux. Basal taurine efflux varied inversely with the extracellular concentration of Ca2+ over the concentration range 0-5.0 mM. The observed Ca2+ dependence is consistent with a role for Ca2+ in the regulation of taurine release. Furthermore, taurine release from astrocytes in response to elevated K+ may reflect a neuromodulatory role for this amino acid in the CNS.
D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology*; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology*; D002851:Chromatography, High Pressure Liquid; D004305:Dose-Response Relationship, Drug; D004533:Egtazic Acid / Q000494:pharmacology; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D018377:Neurotransmitter Agents / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology*; D051381:Rats; D013654:Taurine / Q000378:metabolism*; D014701:Veratridine / Q000494:pharmacology
D018377:Neurotransmitter Agents; D013654:Taurine; D004533:Egtazic Acid; D014701:Veratridine; D008274:Magnesium; D011188:Potassium; D002118:Calcium