Molecular mechanism of production and removal of neurotransmitters.

为了研究渗透压转运蛋白在中枢神经系统细胞渗透调节机制中的作用，我们利用ISH和Northern印迹技术分析了渗透压转运蛋白肌醇、甜菜碱、牛磺酸和谷氨酸转运蛋白在脱水动物模型中的脑定位和基因表达。肌醇转运蛋白在脑中的表达最高，其基因表达受血清渗透压梯度的调节。此外，在大鼠大脑中动脉阻塞和脑水肿模型中，肌醇转运蛋白的基因表达和转录水平不仅在病变部位增加，而且广泛延伸到病变周围。此外，在大鼠视网膜渗透压负荷模型中，急性压力负荷引起肌醇转运蛋白mRNA的表达增加，而慢性压力负荷则选择性地增加牛磺酸转运蛋白mRNA的表达。以上结果表明，渗透压转运蛋白的表达根据渗透刺激的种类和病变的不同而受到不同的调节。这一实验成功地分离了一种新的多肽组氨酸转运蛋白(PHT1)，并证明了其一级结构，该转运蛋白在神经系统中特异表达。最后，通过对非洲爪哇卵母细胞中多种表达的研究表明，肌肽、寡肽和组氨酸与新的转运蛋白具有高度的亲和力，并以质子依赖的方式运输。

To examine the types of osmolite transporters involved in cytophylactic mechanisms in response to osmotic changes in the CNS,we analyzed the cerebral localization and the genetic expression of a number of transporter molecules including Myoinositol, an osmolite transporter, Betaine, Taurine and Glutamic acid transporters in an animal model of dehydration using ISH and northern blotting techniques. Myoinositol transporter was found to be the most expressed in the brain and its genetic expression shown to be regulated by blood serum osmotic pressure gradient.Moreover, in rat middle cerebral artery obstruction and in cerebral edema models, the increase of both the genetic expression and the transcription of myoinositol transporter was noticed not only in the lesion site, but was also widely extended to the peri-lesional area. Further, in osmotic pressure load models in the rat retina, an acute pressure load induced an increase of myoinositol transporter mRNA while a while a chronic pressure load to the retina selectively increased Taurine transporter mRNA.It is suggested from the above findings that the expression of osmolite transporter is differently regulated according to the kind of osmotic stimulus and to the lesion topography.Next, an attempt was made to isolate a new transporter molecule bearing osmotic pressure response. This experience resulted in the successful isolation of the cDNA and the demonstration of the primary structure of a new Peptide Histidine Transporter (PHT1) which is specifically expressed in the nervous system.Finally, from the study of a variety of expressions in the Xenopus oocytes, it was shown that carnosine, oligopeptides and histidine are transported in high affinity with the new transporter and in a proton-depended way.