cDNA cloning of blood-brain barrier neurotransmitter transporter and analysis of its physiological function

本研究的目的是阐明神经递质在血脑屏障（BBB）上的转运机制。作为体外BBB模型，使用条件永生化脑毛细血管内皮细胞系。采用脑外排指数（BEI）法测定大鼠体内血脑屏障外排率。我们已经阐明，Na^+依赖的立体选择性天冬氨酸转运系统在血脑屏障发挥作用。ASCT可能是脑毛细血管内皮细胞选择性转运L-Asp的候选药物。γ-氨基丁酸（GABA）可通过血脑屏障（BBB）从脑转运至血液。GAT-2/BGT 1可能是GABA在血脑屏障的主要转运蛋白。有机阴离子转运多肽2（oatp 2）被认为是血脑屏障上脱氢表雄酮硫酸酯和雌酮-3-硫酸酯的负责转运蛋白。此外，我们还发现脑毛细血管内皮细胞中有肾上腺素和去甲肾上腺素转运蛋白。这些新发现提示，当脑间质液中神经递质含量过多时，血脑屏障可能对中枢神经系统起重要的生理拯救作用。这是血脑屏障研究中的一个新发现，对今后的研究具有重要的推动作用。

The purpose of the present study is to clarify the neurotransmitter transport mechanism at the blood-brain barrier (BBB). As in vitro BBB model, a conditionally immortalized brain capillary endothelial cell line was used. The Brain Efflux Index (BEI) method was used to determine the in vivo BBB efflux rate in rats. We have clarified that Na^+ dependent stereo-selective aspartic acid transport system was functioning at the BBB. ASCT was suggested for the potential candidate of the L-Asp selective transport in the brain capillary endothelial cells. It was demonstrated that γ-aminobutylic acid (GABA) was transported from the brain to the blood across the BBB. GAT-2/BGT1 was suggested for the responsible transporter protein of GABA at the BBB. Organic anion transporting polypeptide 2 (oatp2) was suggested for the responsible transporter of dehydroepiandrosterone sulfate and estrone-3-sulfate at the BBB. Moreover, we have found that the brain capillary endothelial cells have the serotonine and norepinephrine transpot proteins. These new findings suggested that the BBB would play an important physiological role of rescue system for the central nervous system when there would be excess amount of neuretransmitters in the brain interstitial fluid. This is a quite new finding in the blood-brain barrier research and will significantly stimulate the progress of the future research.