Chloride-dependent binding sites for L-[3H]glutamate on dendrodendritic synaptosomal membranes of rat olfactory bulb.
Chloride-dependent binding sites for L-[3H]glutamate on dendrodendritic synaptosomal membranes of rat olfactory bulb.
复制标题
大鼠嗅球树突突触体膜上 L-[3H]谷氨酸的氯依赖性结合位点。
DOI：
10.1002/jnr.490160208
复制
发表时间：
1986
影响因子：
4.2
通讯作者：
Spraguer,PA
中科院分区：
文献类型：
--
作者：
Quinn,MR;Spraguer,PA
树突触发生在嗅球内的颗粒细胞树突和二尖瓣细胞的次级树突之间，并可在亚细胞部分(DDS)中获得。由于二尖瓣细胞被认为利用兴奋性氨基酸作为神经递质，我们测定了在50 mM Tris-HCI，pH 7.1的条件下，不依赖Na+的L[~3H]谷氨酸与DDS新鲜膜结合的药理特异性。L-谷氨酸与DDS膜的结合具有特异性、CI-−依赖性和可饱和性。用计算机程序Ligand对Scatchard图进行了非线性回归分析，数据符合单点模型，KD值为0.56±0.04μM，表观Bmax为48±5pmol/mg蛋白。Hill图也表明只有一个位点存在，没有协同作用(NH=0.99±0.03)。然而，几种化合物抑制L-谷氨酸与DDS膜结合的相对有效性清楚地表明存在不止一个位点。电生理学研究表明，2-氨基-4-膦酸丁酸酯是模拟二尖瓣细胞轴突诱发反应的有效拮抗剂，喹乙醇是一种有效的激动剂，这两种化合物都是L谷氨酸与DDS膜结合的高效拮抗剂。用200 nM L-谷氨酸标记的tke位点，约有70%被置换，K1值为1.6μM，而对L-谷氨酸结合的准定量抑制产生一条曲线，并被分解成两个亲和力相对较高的位点(K1值分别为0.02和0.65μM)。其他几种化合物，包括N-甲基-D-天冬氨酸和红藻氨酸，是相对无效的抑制剂。尽管在该制剂中发现了少量CI−非依赖性的L-谷氨酸结合，但CI−依赖的结合位点占主导地位，并被clacium刺激。这些结果表明，L-谷氨酸，或一种密切相关的化合物，在嗅球的树-树突触中起着重要作用。
Dendrodendritic synapses occur between granule cell dendrites and secondary dendrites of mitral cells within the olfactory bulb and are attainable in a subcellular fraction (DDS). Since the mitral cells are thought to utilize an excitatory amino acid as a neurotransmitter, we determined the pharmacologic specificity of Na+‐independent L‐[3H]glutamate binding to fresh membrances of DDS in 50 mM Tris‐HCI, pH 7.1. Binding of L‐glutamate to membrances of DDS was specific, CI−dependent, and saturable. Scatchard plots were analyzed by nonlinear regression analysee using the computer program LIGAND, and the data was best‐fitted to a one‐site model with KDof 0.56 ± 0.04 μM and an apparent Bmaxof 48 ± 5 pmol/mg protein. Hill plots also indicated the presence of one site and no cooperativity (nH= 0.99 ± 0.03). However, the relative effictiveness of several compounds in inhibiting L‐glutamate binding to membranes of DDS clearly demonstrated the presence of more than one site. Electrophysiological studies suggest that 2‐amino‐4‐phosphonobutyrate (APB) is a potent antagonist of evoked responses elicited by simulation of mitral cell axons and that quisqualate is a potent agonist; both of these compounds were highly effective inhibitors of L‐glutamate binding to DDS membrances. APB displaced about 70% of tke sites labeled with 200 nM L‐glutamate with a K1of 1.6 μM, whereas quisqualate inhibition of L‐glutamate binding yielded a line that was curvilinear in the Scatchard plot and was resolved into two sites of relatively high affinity (K1values of 0.02 and 0.65 μM). Several other compounds, including N‐methyl‐D‐aspartate and kainate, were relatively ineffective inhibitors. Although a small amount of CI−‐independent L‐glutamate binding was demonstrable in the preparation, CI−‐dependent sites predominated and were stimulated by clacium. These results suggest an important role of L‐glutamate, or a closely related compound, at dendrodendritic synapses of the olfactory bulb.