Marc R E, Liu W L, Kalloniatis M, Raiguel S F, van Haesendonck E
University of Texas Graduate School of Biomedical Sciences, Sensory Sciences Center, Houston 77030.
J Neurosci. 1990 Dec;10(12):4006-34. doi: 10.1523/JNEUROSCI.10-12-04006.1990.
Postembedding silver-intensified immunogold procedures reveal high levels of glutamate immunoreactivity in "vertical" elements of the goldfish retina: (1) Red-sensitive and green-sensitive cones display strong glutamate immunoreactivity, especially in their synaptic terminals, but blue-sensitive cones are poorly immunoreactive. (2) All type Mb (on-center) and Ma (off-center) mixed rod-cone bipolar cells and all identifiable cone bipolar cells are highly glutamate immunoreactive. We find no evidence for bipolar cells that lack glutamate immunoreactivity. (3) The majority of the somas in the ganglion cell layer and certain large cells of the amacrine cell layer resembling displaced ganglion cells are strongly glutamate immunoreactive. (4) Despite their high affinity symport of acidic amino acids, the endogenous levels of glutamate in Müller's cells are among the lowest in the retina. (5) GABAergic neurons possess intermediate levels of glutamate immunoreactivity. Quantitative immunocytochemistry coupled with digital image analysis allows estimates of intracellular glutamate levels. Photoreceptors and bipolar and ganglion cells contain from 1 to 10 mM glutamate. The bipolar and ganglion cell populations maintain high intracellular glutamate concentrations, averaging about 5 mM, whereas red-sensitive and green-sensitive cones apparently maintain lower levels. Importantly, photoreceptor glutamate levels are extremely volatile, and in vitro maintenance is required to preserve cone glutamate immunoreactivity in the goldfish. GABAergic horizontal and amacrine cells contain about 0.3-0.7 mM glutamate, which matches the values predicted from the Km of glutamic acid decarboxylase. Müller's cells and non-GABAergic amacrine cells contain less than 0.1 mM glutamate. Though Müller's cells are known to possess potent glutamate symport, they clearly possess equally potent mechanisms for maintaining low intracellular glutamate concentrations.
包埋后银增强免疫金法显示，金鱼视网膜的“垂直”细胞成分中存在高水平的谷氨酸免疫反应性：（1）对红光敏感和对绿光敏感的视锥细胞显示出强烈的谷氨酸免疫反应性，尤其是在它们的突触终末，但对蓝光敏感的视锥细胞免疫反应性较弱。（2）所有Mb型（中心兴奋）和Ma型（中心抑制）混合视杆 - 视锥双极细胞以及所有可识别的视锥双极细胞都具有高度的谷氨酸免疫反应性。我们没有发现缺乏谷氨酸免疫反应性的双极细胞的证据。（3）神经节细胞层中的大多数细胞体以及无长突细胞层中某些类似于移位神经节细胞的大细胞具有强烈的谷氨酸免疫反应性。（4）尽管米勒细胞对酸性氨基酸具有高亲和力同向转运，但视网膜中米勒细胞内谷氨酸的内源性水平是最低的之一。（5）γ-氨基丁酸能神经元具有中等水平的谷氨酸免疫反应性。定量免疫细胞化学结合数字图像分析可以估计细胞内谷氨酸水平。光感受器、双极细胞和神经节细胞含有1至10 mM的谷氨酸。双极细胞和神经节细胞群体维持较高的细胞内谷氨酸浓度，平均约为5 mM，而对红光敏感和对绿光敏感的视锥细胞显然维持较低水平。重要的是，光感受器谷氨酸水平极易变化，在体外培养是保持金鱼视锥细胞谷氨酸免疫反应性所必需的。γ-氨基丁酸能水平细胞和无长突细胞含有约0.3 - 0.7 mM的谷氨酸，这与根据谷氨酸脱羧酶的米氏常数预测的值相符。米勒细胞和非γ-氨基丁酸能无长突细胞含有少于0.1 mM的谷氨酸。尽管已知米勒细胞具有强大的谷氨酸同向转运，但它们显然也具有同样强大的机制来维持低细胞内谷氨酸浓度。
