Exploration of endogenous novel ligands for glutamate receptors with a high sub-type specificities

在这项研究中，我们对中枢氨基酸信号系统的机制有两个发现：具有立体选择性的谷氨酸转运体在小脑中的特异性表达--脑组织中依赖Na+的、高亲和力的L-谷氨酸转运体(GLUT)已成为一个重要的研究热点，特别是因为已经发现GLUT的异常可能与严重的神经疾病有关。我们用定量放射自显影技术研究了具有底物识别/结合位点特征的放射性配基在GLUT上的分布和药理学。我们测定了非放射性对L和D-天冬氨酸结合的抑制IC_(50)值。这两个放射性配体在与前脑中的结合部位的相互作用方面没有明显的不同，与该区域的所有依赖于Na+的GLUT结合部位没有…的立体选择性一致更多或天冬氨酸对映体。然而，在小脑皮质，数据表明存在过剩的结合位点垫，更倾向于L-而不是D-天冬氨酸。这些发现与之前许多关于小脑皮质的研究结果形成了鲜明对比。存在一种具有谷氨酸转运体性质的未知分子的可能性是值得考虑的。一种新的L-丝氨酸转运体在中枢神经系统中被报道，L-丝氨酸(Serine，Ser)可诱导突触后抑制电位，但其神经传递机制尚不清楚。我们在大鼠脑内发现了一种新的高亲和力摄取L-丝氨酸的活性。其中一半不依赖于Na+浓度，它由两个以上不同的转运蛋白系统组成。D-天冬氨酸和L-丝氨酸具有不同于已知氨基酸转运体的药理特征。根据这些发现和本研究的其他结果，我们强烈地认为D-天冬氨酸和L-丝氨酸在经典的神经活性氨基酸之外还具有神经递质的作用。较少

In this research project we obtained two findings on the mechanism of central amino acids-signaling system as follows:Expression specifically in cerebellum of glutamate transporters with stereo-selectivity - The Na^+-dependent, "high-affinity" transport of L-glutamate (GluT) in brain tissue has become a significant focus of interest, particularly since it has been revealed that abnormalities of GluT may be associated with serious neurological disorders. Using quantitative autaradiography, we have studied the distribution and pharmacology of radioligand binding to sites with characteristics of the substrate-recognition/binding locus on GluT. We have determined IC_<50> values for the inhibition of [^3H]L- and [^3H]D-Asp binding by their non-radioactive counterparts. The two radioligands did not appreciably differ from each other in then interactions with the binding sites in the forebrain, consistent with all Na^+-dependent GluT binding sites in that region having no stereo-selectivity f … More or aspartate enantiomers. In the cerebellar cortex, however, the data indicated the presence of a GluT binding site mat preferred L- over D-aspartate. These findings contrast with many previous in cerebellar cortex. A possibility of an existence of hitherto unknown molecules with properties of a glutamate transporter should be considered.A novel L-serine transporters in central nervous system-It was reported that L-serine (Ser) induces postsynaptic inhibitory potentials; however, little is elucidated about the mechanism of its neuro-transmission. We found here a novel high affinity uptake activity for L-Ser in rat brain. A half of that is not dependent on Na^+ concentration and it was composed by more than two different transporters systems. Pharmacological characteristics of that was distinct from known amino acid transportersAccording to these findings and other results in this research project, it is strongly suggested that D-Asp and L-Ser play a role for neuronal transmission beside classical neuroactive amino acids. Less