Beetsch J W, Olson J E
Department of Emergency Medicine, Wright State University School of Medicine, Dayton, OH 45401.
Brain Res. 1993 Jun 4;613(1):10-5. doi: 10.1016/0006-8993(93)90447-u.
[3H]Taurine uptake and release was characterized in astrocytes from rat cerebral cortex grown in normal and hyperosmotic culture conditions to investigate mechanisms of cell volume regulation and adaptation to states of altered osmolality. In high concentrations of taurine (1 mM), uptake was linear in both osmotic conditions for at least 30 min. The uptake rate in 1 mM taurine was not affected by exposure to hyperosmotic conditions. The mean +/- S.E.M. apparent binding constant for carrier-mediated taurine transport, Km, was not altered by hyperosmotic conditions (22.8 +/- 5.1 microM in iso-osmotic media, 21.3 +/- 11.9 microM in hyperosmotic media). However, maximal velocity of uptake, Vmax (mean +/- S.E.M.), of taurine was significantly lower in hyperosmotically treated astrocytes (0.175 +/- 0.035 nmol/mg protein.min) compared with the Vmax of iso-osmotically treated astrocytes (0.299 +/- 0.026 nmol/mg protein.min). The diffusional transport rate, Kdiff, was not affected by growth in hyperosmotic conditions (0.221 +/- 0.033 microliter/mg protein.min in iso-osmotic media, 0.295 +/- 0.043 microliter/mg protein.min in hyperosmotic media). Taurine release rate, expressed as a percent of the total cell content, was not affected by hyperosmotic exposure. However, astrocytes grown in hyperosmotic conditions contain nearly 60% more taurine than control cells. Thus, the absolute rate of taurine release (mean +/- S.E.M.) was significantly larger (P < 0.05) in hyperosmotic cells (0.1592 +/- 0.0082 nmol/mg protein.min) compared with control cells (0.0943 +/- 0.0096 nmol/mg protein.min). Quantitative analysis of these data indicate that maintenance of elevated taurine contents by cultured cerebral astrocytes exposed to hyperosmotic conditions is not due to alterations in rates of transport.
研究细胞体积调节机制以及适应渗透压改变状态的机制时，对在正常和高渗培养条件下生长的大鼠大脑皮质星形胶质细胞中的[3H]牛磺酸摄取和释放进行了表征。在高浓度牛磺酸（1 mM）下，两种渗透压条件下的摄取在至少30分钟内呈线性。1 mM牛磺酸的摄取速率不受高渗条件暴露的影响。载体介导的牛磺酸转运的平均±标准误表观结合常数Km，不受高渗条件影响（等渗培养基中为22.8±5.1 microM，高渗培养基中为21.3±11.9 microM）。然而，与等渗处理的星形胶质细胞的Vmax（0.299±0.026 nmol/mg蛋白质·分钟）相比，高渗处理的星形胶质细胞中牛磺酸的摄取最大速度Vmax（平均±标准误）显著更低（0.175±0.035 nmol/mg蛋白质·分钟）。扩散转运速率Kdiff不受高渗条件下生长的影响（等渗培养基中为0.221±0.033微升/mg蛋白质·分钟，高渗培养基中为0.295±0.043微升/mg蛋白质·分钟）。以总细胞含量的百分比表示的牛磺酸释放速率不受高渗暴露的影响。然而，在高渗条件下生长的星形胶质细胞所含牛磺酸比对照细胞多近60%。因此，与对照细胞（0.0943±0.0096 nmol/mg蛋白质·分钟）相比，高渗细胞中牛磺酸的绝对释放速率（平均±标准误）显著更大（P<0.05）（0.1592±0.0082 nmol/mg蛋白质·分钟）。对这些数据的定量分析表明，暴露于高渗条件下的培养大脑星形胶质细胞维持较高牛磺酸含量并非由于转运速率的改变。
