Yang C Y, Brecha N C, Tsao E
Department of Neurobiology and Behavior, State University of New York at Stony Brook, 11794-5230, USA.
J Comp Neurol. 1997 Dec 8;389(1):117-26. doi: 10.1002/(sici)1096-9861(19971208)389:1<117::aid-cne8>3.0.co;2-5.
Gamma-aminobutyric acid (GABA) plasma membrane transporters (GATs) play an important role in regulating GABA neurotransmission in the nervous system. The distribution of two GATs, GAT 1 and GAT 3, in salamander retina was investigated by using affinity-purified polyclonal antisera directed to the predicted C-terminals of rat GAT 1 and rat GAT 3. GAT 1-immunoreactivity (-IR) was found in type IB and IIB orthotopic bipolar cells (BCs) located in the distal and middle of the inner nuclear layer (INL), respectively; in type IIA and IA amacrine cells (ACs) located in the middle and proximal INL, respectively; and in interplexiform cells and cells in the ganglion cell layer (GCL). No detectable staining was found in horizontal cells (HCs) or in structures resembling Müller cells. GAT 1-immunoreactive fibers were present in the outer plexiform layer (OPL) and inner plexiform layer (IPL) in three bands corresponding to the three bands previously reported to be GABA-IR. GAT 3 antibodies labeled fewer cells and cell types than GAT 1 antibodies. GAT 3-IR was localized to type IIA and IA ACs and cells in the GCL, but not to BCs, HCs, or Müller cell-like structures. There was weak labeling of the OPL and stronger labeling of the IPL, with three distinct bands at the same depth as observed with GAT 1-IR. Double-labeling showed that the majority of GAT 1-IR BCs (88%), ACs (88%), and cells in the GCL (78%) colocalized with GABA-IR. The present study provides the first direct evidence of the expression of two GAT subtypes in neurons of nonmammalian retinas. These transporters could regulate GABA neurotransmission by reuptake and termination of GABA's action and, perhaps, by GABA release mechanisms. The presence of GAT 1-IR/GABA-IR bipolar cells further supports our earlier observations that a subgroup of orthotopic bipolar cells are likely to be GABAergic.
γ-氨基丁酸（GABA）质膜转运体（GATs）在调节神经系统中的GABA神经传递方面发挥着重要作用。利用针对大鼠GAT 1和大鼠GAT 3预测C端的亲和纯化多克隆抗血清，研究了两种GATs（GAT 1和GAT 3）在蝾螈视网膜中的分布。GAT 1免疫反应性（-IR）分别在位于内核层（INL）远端和中部的IB型和IIB型原位双极细胞（BCs）中发现；分别在位于INL中部和近端的IIA型和IA型无长突细胞（ACs）中发现；以及在网间细胞和神经节细胞层（GCL）中的细胞中发现。在水平细胞（HCs）或类似米勒细胞的结构中未发现可检测到的染色。GAT 1免疫反应性纤维存在于外网状层（OPL）和内网状层（IPL）中，呈三条带，与先前报道的三条GABA-IR带相对应。GAT 3抗体标记的细胞和细胞类型比GAT 1抗体少。GAT 3-IR定位于IIA型和IA型ACs以及GCL中的细胞，但不定位于BCs、HCs或类似米勒细胞的结构。OPL有较弱的标记，IPL有较强的标记，在与GAT 1-IR观察到的相同深度处有三条明显的带。双重标记显示，大多数GAT 1-IR BCs（88%）、ACs（88%）和GCL中的细胞（78%）与GABA-IR共定位。本研究提供了非哺乳动物视网膜神经元中两种GAT亚型表达的首个直接证据。这些转运体可通过GABA的再摄取和作用终止，或许还通过GABA释放机制来调节GABA神经传递。GAT 1-IR/GABA-IR双极细胞的存在进一步支持了我们早期的观察结果，即原位双极细胞的一个亚群可能是GABA能的。
