Jiang Zheng, Li Baoqin, Jursky Frantisek, Shen Wen
Department of Biomedical Science, Florida Atlantic University, Boca Raton, Florida 33431, USA.
Vis Neurosci. 2007 Mar-Apr;24(2):157-68. doi: 10.1017/S0952523807070186.
Amphibian retinas are commonly used for electrophysiological studies on neural function and transduction because they share the same general properties as higher vertebrate retinas. Glycinergic synapses have been well described in amphibian retinas. However, the role of glycine transporters in the synapses is largely unknown. We studied the distribution and function of glycine transporters in the retinas from tiger salamanders, mudpuppies, and leopard frogs by immunofluorescence labeling and whole-cell recording methods. Our results indicated that GlyT1- and GlyT2-like transporters were present in Müller cells and neurons, respectively. GlyT1 labeling was present in Müller glial cells and co-localized with Glial fibrillary acidic protein (GFAP), a Müller cell marker, whereas the GlyT2 immunoreactivity was present in the somas of amacrine cells (ACs) and processes in the inner plexiform layer (IPL) and the outer plexiform layer (OPL). Because the axon processes of glycinergic interplexiform cells (IPCs) are the only source of glycine input in the OPL, GlyT2 staining revealed a spatial pattern of the axon processes of IPCs in the OPL. The function of GlyT2 in the IPCs was studied in tiger salamander retinal horizontal cells (HCs) by whole-cell gramicidin perforated recording. The results demonstrated that inhibition of GlyT2 by a specific inhibitor, amoxapine, increased a tonic glycine input to HCs. Thus, the GlyT2 transporter is responsible for uptake of synaptic glycine in the outer retina. We also compared the distribution of glycine transporters in other amphibian species: salamander, mudpuppy, and frog. The results are consistent with the general pattern that GlyT1-like transporters are present in Müller cells and GlyT2-like transporters in neurons in amphibian retinas.
两栖动物的视网膜常用于神经功能和转导的电生理研究，因为它们与高等脊椎动物的视网膜具有相同的一般特性。甘氨酸能突触在两栖动物视网膜中已有充分描述。然而，甘氨酸转运体在突触中的作用在很大程度上尚不清楚。我们通过免疫荧光标记和全细胞记录方法研究了虎螈、泥螈和豹蛙视网膜中甘氨酸转运体的分布和功能。我们的结果表明，GlyT1样和GlyT2样转运体分别存在于米勒细胞和神经元中。GlyT1标记存在于米勒胶质细胞中，并与米勒细胞标志物胶质纤维酸性蛋白（GFAP）共定位，而GlyT2免疫反应性存在于无长突细胞（ACs）的胞体以及内网状层（IPL）和外网状层（OPL）的突起中。由于甘氨酸能网间细胞（IPCs）的轴突是OPL中甘氨酸输入的唯一来源，GlyT2染色揭示了IPCs在OPL中轴突的空间分布模式。通过全细胞膜片钳穿孔记录，在虎螈视网膜水平细胞（HCs）中研究了GlyT2在IPCs中的功能。结果表明，特异性抑制剂阿莫沙平对GlyT2的抑制增加了HCs的持续性甘氨酸输入。因此，GlyT2转运体负责外视网膜中突触甘氨酸的摄取。我们还比较了其他两栖动物物种（蝾螈、泥螈和青蛙）中甘氨酸转运体的分布。结果与两栖动物视网膜中GlyT1样转运体存在于米勒细胞中、GlyT2样转运体存在于神经元中的一般模式一致。
