Pessin M, Adler R
J Neurosci Res. 1985;14(3):317-28. doi: 10.1002/jnr.490140304.
We report here that high-affinity uptake mechanisms for two or three putative neurotransmitter molecules coexist in many of the neurons present in glia-free, purified neuronal monolayers from chick embryo retina. Replicate cultures were incubated with the tritiated forms of the amino acids gamma-aminobutyric acid (GABA), taurine (TAU) and aspartate (ASP) either individually or in binary or tertiary combinations. Incubation conditions were those typically used to analyze high-affinity uptake mechanisms. At the end of the incubation period the cultures were either lysed in water for measurement of intracellular radioactivity by liquid scintillation counting, or fixed in glutaraldehyde and prepared for autoradiography. Our results indicate that there is coexistence of uptake mechanisms for putative neurotransmitters in retinal cells. Biochemical measurements showed that, at the concentrations used in these experiments, two or more radioactive amino acids could be taken up simultaneously by the cultured populations without extensive inhibition. Moreover, the percentage of cells that appeared autoradiographically labeled in cultures exposed to two or more radioactive amino acid was less than the sum of the percentages of labeled cells when each amino acid was applied individually. Numerical analysis of the autoradiographs was carried out to determine the percentage of cells that could take up only one, only two, or the three putative amino acid neurotransmitters under investigation. This analysis showed that approximately 20% of the neurons have only the mechanism for TAU, whereas very few if any neurons have high-affinity uptake mechanisms for GABA alone or ASP alone. Our experiments have identified populations of cells that take up GABA and TAU (but not ASP) or ASP and TAU (but not GABA). Interestingly, we have not seen any neurons that can take up ASP and GABA and cannot take up TAU, although as many as 50% of the neurons can take up ASP, GABA, and TAU simultaneously. By showing simultaneous uptake of different putative neurotransmitters within individual neurons, our results emphasize the concept that the presence in a given neuron of a high-affinity uptake mechanism for a particular molecule is not a sufficient criterion to assign a neurotransmitter function to that molecule in that neuron.
我们在此报告，在来自鸡胚视网膜的无胶质、纯化的神经元单层中存在的许多神经元里，两种或三种假定神经递质分子的高亲和力摄取机制共存。将复制培养物分别与氨基酸γ-氨基丁酸（GABA）、牛磺酸（TAU）和天冬氨酸（ASP）的氚化形式孵育，或者以二元或三元组合形式孵育。孵育条件是通常用于分析高亲和力摄取机制的条件。在孵育期结束时，培养物要么在水中裂解，通过液体闪烁计数测量细胞内放射性，要么用戊二醛固定并制备用于放射自显影。我们的结果表明视网膜细胞中存在假定神经递质的摄取机制共存。生化测量表明，在这些实验中使用的浓度下，两种或更多种放射性氨基酸可以被培养群体同时摄取而没有广泛的抑制。此外，在暴露于两种或更多种放射性氨基酸的培养物中，放射自显影标记的细胞百分比低于每种氨基酸单独应用时标记细胞百分比的总和。对放射自显影片进行数值分析，以确定能够摄取仅一种、仅两种或所研究的三种假定氨基酸神经递质的细胞百分比。该分析表明，大约20%的神经元仅具有摄取TAU的机制，而几乎没有神经元仅具有摄取GABA或仅摄取ASP的高亲和力摄取机制。我们的实验确定了摄取GABA和TAU（但不摄取ASP）或ASP和TAU（但不摄取GABA）的细胞群体。有趣的是，我们没有看到任何能够摄取ASP和GABA但不能摄取TAU的神经元，尽管多达50%的神经元可以同时摄取ASP、GABA和TAU。通过显示单个神经元内不同假定神经递质的同时摄取，我们的结果强调了这样一个概念，即给定神经元中存在针对特定分子的高亲和力摄取机制，并不是将该分子在该神经元中的神经递质功能赋予该分子的充分标准。
