Binding sites for L-[3H]glutamate on hippocampal synaptic membranes: three populations differentially affected by chloride and calcium ions.
Binding sites for L-[3H]glutamate on hippocampal synaptic membranes: three populations differentially affected by chloride and calcium ions.
复制标题
海马突触膜上 L-[3H]谷氨酸的结合位点：三个群体受氯离子和钙离子的影响不同。
DOI：
10.1111/j.1471-4159.1985.tb07170.x
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发表时间：
1985
影响因子：
4.7
通讯作者：
Werling,LL
中科院分区：
文献类型：
--
作者：
Nadler,JV;Wang,A;Werling,LL
研究了Cl−和Ca 2+对l-[3 H]谷氨酸与大鼠海马突触膜上多个位点特异性结合的影响。使用使君子酸盐（5 μM）或dl-2-氨基-4-膦酰基丁酸盐（2-APB）（300 μM）区分两类先前鉴定的结合位点。在不同离子条件下构建的饱和等温线和位移曲线表明，Cl−和Ca 2+的影响可以通过假设该制剂中存在三个主要结合位点群体而不是两个来最好地解释。L-谷氨酸与Glu A位点的结合表现出对Cl-的绝对依赖性，Ca 2+显著增加了这些位点的最大密度。Glu A位点以相对高的亲和力结合使君子酸和2-APB。Cl−（47 μM）使Glu B位点的最大密度增加了一倍多，但Ca 2+似乎没有影响。Glu B位点可通过其对使君子酸和2-AP B的相对低亲和力与其他类别区分开。有理由认为Glu B群体是异质的。通过将2-APB-敏感性结合位点暴露于含Ca 2+的Tris-HOAc缓冲液中的放射性配体，可以几乎选择性地标记新型Glu C群体。l-[3 H]谷氨酸与这些位点的结合被Cl−和Ca 2+增强，但不需要任何离子。Ca 2+似乎增加了Glu C位点对l-谷氨酸的亲和力及其最大结合位点密度。在Ca 2+和Cl−存在下，Glu C位点以微摩尔亲和力（KD> 2 μM）和高容量（Bmax> 160 pmol/mg蛋白）结合放射性配体。这些结合位点的结构特异性与Glu A位点的结构特异性非常相似，但这些位点以约一个数量级的低亲和力结合兴奋剂。Glu C结合位点表现出与海马结构中的突触受体功能相容的特征。
The effects of Cl−and Ca2+were studied on the specific binding ofl‐[3H]glutamate to multiple sites on rat hippocampal synaptic membranes. Quisqualate (5 μM) ordl‐2‐amino‐4‐phosphonobutyrate (2‐APB) (300 μM) was used to discriminate two previously identified classes of binding sites. Saturation isotherms and displacement curves constructed under different ionic conditions suggested that the effects of Cl−and Ca2+could best be explained by postulating the existence of three major binding site populations in this preparation rather than two. The binding ofl‐glutamate to Glu A sites exhibits an absolute dependence on Cl−, and Ca2+markedly increases the maximum density of these sites. Glu A sites bind quisqualate and 2‐APB with relatively high affinity. Cl−(47 μM) more than doubles the maximum density of Glu B sites, but Ca2+appears to have no effect. Glu B sites can be discriminated from the other classes by their relatively low affinity for quisqualate and 2‐APB. There is reason to think that the Glu B population is heterogeneous. The novel Glu C population can be virtually selectively labeled by exposing 2‐APB‐sensitive binding sites to radioligand in Tris‐HOAc buffer with Ca2+. Binding ofl‐[3H]glutamate to these sites is enhanced by both Cl−and Ca2+, but requires neither ion. Ca2+appears to increase both the affinity of Glu C sites forl‐glutamate and their maximum binding site density. In the presence of Ca2+and Cl−, Glu C sites bind the radioligand with micromolar affinity (KD> 2 μM) and high capacity (Bmax> 160 pmol/mg protein). The structural specificity of these binding sites closely resembles that of Glu A sites, but these sites bind excitants with about an order of magnitude lower affinity. The Glu C binding sites exhibit characteristics compatible with a synaptic receptor function in the hippocampal formation.