Substrates and temperature differentiate ion flux from serotonin flux in a serotonin transporter
Substrates and temperature differentiate ion flux from serotonin flux in a serotonin transporter
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DOI：
10.1016/s0028-3908(00)00191-x
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发表时间：
2001-03-01
影响因子：
4.7
通讯作者：
Quick, MW
中科院分区：
文献类型：
--
作者：
Beckman, ML;Quick, MW
神经递质转运蛋白将递质的转运与其浓度梯度耦合到也被转运的相关离子的电化学电势。最近的一些神经递质转运蛋白的研究表明，他们有传统的载体和底物依赖性离子通道的属性，在离子通量超过化学计量底物通量预测。这些特性是否对所有转运蛋白都具有可比性，这些渗透状态在多大程度上是独立的，以及这两种状态之间的关系是否可以调节，目前还不清楚。为了解决这些问题，我们表达了果蝇5-羟色胺（5-HT）转运蛋白（dSERT）在非洲爪蟾卵母细胞和测量两个底物引起的离子通量和SPIT通量在不同的温度和底物浓度。我们发现，传输过程的离子通量和SPIT通量分量具有显著的温度依赖性，这表明离子通量和发射通量来自涉及大的构象变化的类似的化学耦合过程（例如，门控）。这些数据与谷氨酸转运蛋白所示的数据相反，表明5 HT转运蛋白的渗透过程不同。离子通量和5 HT通量之间的关系是由氯离子和5 HT差异调节，这表明这些渗透状态是不同的。在介导离子通量和SPIT通量所需的半最大5 HT浓度的差异发生在亚微摩尔SPIT浓度下，这表明dSERT在离子通量和SPIT通量中的相对参与将由突触SPIT浓度决定。(C)2001爱思唯尔科技有限公司版权所有。
Neurotransmitter transporters couple the transport of transmitter against its concentration gradient to the electrochemical potential of associated ions which are also transported. Recent studies of some neurotransmitter transporters show them to have properties of both traditional carriers and substrate-dependent ion channels, in that ion fluxes are in excess of that predicted from stoichiometric substrate fluxes. Whether these properties are comparable for all transporters, the extent to which these permeation states are independent, and whether the relationship between these two states can be regulated are not well understood. To address these questions, we expressed the Drosophila serotonin (5HT) transporter (dSERT) in Xenopus oocytes and measured both substrate-elicited ion flux and SPIT flux at various temperatures and substrate concentrations. We find that the ion flux and SPIT flux components of the transport process have a significant temperature dependence suggesting that ion flux and transmitter flux arise from a similar thermodynamically-coupled process involving large conformational changes (e.g., gating). These data are in contrast to those shown for glutamate transporters, suggesting a different permeation process for 5HT transporters. The relationship between ion flux and 5HT flux is differentially regulated by chloride and 5HT, suggesting that these permeation states are distinct. The difference in half-maximal 5HT concentration necessary to mediate ion flux and SPIT flux occurs at submicromolar SPIT concentrations suggesting that the relative participation of dSERT in ion flux and SPIT flux will be determined by the synaptic SPIT concentration. (C) 2001 Elsevier Science Ltd. All rights reserved.