Keep R F, Xiang J
Department of Surgery (Neurosurgery), University of Michigan, Ann Arbor 48109-0532, USA.
Brain Res. 1996 Apr 9;715(1-2):17-24. doi: 10.1016/0006-8993(95)01294-X.
The putative osmoregulatory agent, taurine, is lost from the brain during hypo-osmotic stress or ischemia, but the regulatory mechanisms involved in this loss have not been fully elucidated. In this study, we have examined taurine transport by the isolated rat choroid plexus, one element of the brain-blood interface, and examined how it may be regulated as part of brain volume regulation. Choroid plexus taurine uptake was Na- and Cl-dependent with a Vmax and Km of 6.5 +/- 0.3 pmol/mg/min and 232 +/- 33 microM. The latter is substantially greater than the normal CSF taurine concentration and this may be important in removing taurine released into the CSF during parenchymal cell swelling. Taurine uptake also appears calmodulin dependent as it was reduced by 84 and 91% in the presence of 25 microM trifluoperazine and 100 microM W-7, two calmodulin inhibitors. Taurine efflux from choroid plexus was stimulated by trifluoperazine, taurine, and hypo-osmotic stress. The latter two effects were reduced by niflumic acid, suggesting that taurine and hypo-osmotic stress act on the same pathway. The stimulation of efflux by hypo-osmotic stress decreased with time, whereas the effect of external taurine was sustained. If this efflux pathway is involved in the movement of taurine from choroid plexus to blood, these results suggest that changes in extracellular taurine may be more important than the direct effect of hypo-osmolality in the long-term loss of taurine from the brain.
假定的渗透调节因子牛磺酸，在低渗应激或缺血期间会从大脑中流失，但其流失所涉及的调节机制尚未完全阐明。在本研究中，我们检测了分离的大鼠脉络丛（脑血界面的一个组成部分）对牛磺酸的转运，并研究了其作为脑容量调节的一部分可能如何被调节。脉络丛对牛磺酸的摄取依赖于钠离子和氯离子，其最大转运速率（Vmax）和米氏常数（Km）分别为6.5±0.3皮摩尔/毫克/分钟和232±33微摩尔。后者显著高于正常脑脊液中牛磺酸的浓度，这对于清除实质细胞肿胀期间释放到脑脊液中的牛磺酸可能很重要。牛磺酸的摄取似乎也依赖于钙调蛋白，因为在存在25微摩尔三氟拉嗪和100微摩尔W-7（两种钙调蛋白抑制剂）的情况下，摄取量分别降低了84%和91%。三氟拉嗪、牛磺酸和低渗应激可刺激脉络丛中牛磺酸的流出。后两种作用可被氟尼酸减弱，这表明牛磺酸和低渗应激作用于同一路径。低渗应激对流出的刺激作用随时间减弱，而外源性牛磺酸的作用则持续存在。如果这种流出途径参与了牛磺酸从脉络丛向血液的转运，那么这些结果表明，细胞外牛磺酸的变化可能比低渗对牛磺酸从大脑长期流失的直接影响更为重要。
