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Ionic Currents in the Human Serotonin Transporter Reveal Inconsistencies in the Alternating Access Hypothesis

机译:人类血清素转运蛋白中的离子流揭示了交替访问假设中的不一致之处。

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摘要

We have investigated the conduction states of human serotonin transporter (hSERT) using the voltage clamp, cut-open frog oocyte method under different internal and external ionic conditions. Our data indicate discrepancies in the alternating access model of cotransport, which cannot consistently explain substrate transport and electrophysiological data. We are able simultaneously to isolate distinct external and internal binding sites for substrate, which exert different effects upon currents conducted by hSERT, in contradiction to the alternating access model. External binding sites of coupled Na ions are likewise simultaneously accessible from the internal and external face. Although Na and Cl are putatively cotransported, they have opposite effects on the internal face of the transporter. Finally, the internal K ion does not compete with internal 5-hydroxytryptamine for empty transporters. These data can be explained more readily in the language of ion channels, rather than carrier models distinguished by alternating access mechanisms: in a channel model of coupled transport, the currents represent different states of the same permeation path through hSERT and coupling occurs in a common pore.
机译:我们已经研究了使用电压钳,切开青蛙卵母细胞方法在不同的内部和外部离子条件下人类血清素转运蛋白(hSERT)的传导状态。我们的数据表明共运输的交替访问模型中的差异,不能始终如一地解释底物运输和电生理数据。我们能够同时分离出不同的底物内部和外部结合位点,这对hSERT传导的电流产生了不同的影响,这与交替访问模型相反。耦合的Na离子的外部结合位点同样可以从内表面和外表面同时访问。尽管推测Na和Cl是共转运的,但它们对转运蛋白的内表面有相反的影响。最后,内部的K离子不会与内部的5-羟色胺竞争空的转运蛋白。这些数据可以用离子通道的语言更容易地解释,而不是通过交替访问机制来区分的载体模型:在耦合传输的通道模型中,电流代表通过hSERT的同一渗透路径的不同状态,并且耦合发生在共同点毛孔。

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