Villanueva S, Orrego F
Department of Physiology and Biophysics, Faculty of Medicine, Universidad de Chile, Santiago.
Brain Res. 1988 Feb 9;440(2):363-5. doi: 10.1016/0006-8993(88)91008-6.
The presence in highly purified rat brain cortex synaptic vesicles of endogenous ligands for rat brain quisqualate receptors was investigated. The vesicles were extracted, and their contents fractionated by high voltage electrophoresis. Endogenous ligands were detected by a radioreceptor assay in which such ligands competed with 50 nM L-[3H]glutamate for binding to quisqualate receptors present in rat brain postsynaptic densities (PSDs). Binding of L-[3H]glutamate to N-methyl-D-aspartate (NMDA) receptors, also present in PSDs, was blocked by 100 microM NMDA. We found that the endogenous ligands present in brain cortex synaptic vesicles for quisqualate receptors, were glutamate and aspartate, in a molar ratio of about two to one. The quisqualate receptor had an affinity 130-fold higher for glutamate (Kd 0.3 microM) than for aspartate, and the latter amino acid also showed a marked negative cooperative for binding (Hill number 0.29, against 0.67 for glutamate). These findings suggest that glutamate is the natural transmitter that activates quisqualate receptors at some central excitatory synapses, and also that aspartate may be a classical transmitter, the receptor for which still remains to be shown.
研究了高纯度大鼠脑皮质突触小泡中是否存在大鼠脑 quisqualate 受体的内源性配体。提取突触小泡，并通过高压电泳对其内容物进行分级分离。通过放射性受体测定法检测内源性配体，在该测定中，此类配体与 50 nM L-[3H]谷氨酸竞争结合大鼠脑突触后致密物（PSD）中存在的 quisqualate 受体。100 μM NMDA 可阻断 L-[3H]谷氨酸与 PSD 中也存在的 N-甲基-D-天冬氨酸（NMDA）受体的结合。我们发现，脑皮质突触小泡中存在的 quisqualate 受体内源性配体为谷氨酸和天冬氨酸，摩尔比约为二比一。quisqualate 受体对谷氨酸（Kd 0.3 μM）的亲和力比对天冬氨酸高 130 倍，并且后者氨基酸在结合时也表现出明显的负协同性（希尔系数为 0.29，而谷氨酸为 0.67）。这些发现表明，谷氨酸是在某些中枢兴奋性突触处激活 quisqualate 受体的天然递质，并且天冬氨酸可能也是一种经典递质，其受体仍有待确定。
