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首页> 外文期刊>American Journal of Physiology >Transition states of the high-affinity rabbit Na(+)/glucose cotransporter SGLT1 as determined from measurement and analysis of voltage-dependent charge movements.
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Transition states of the high-affinity rabbit Na(+)/glucose cotransporter SGLT1 as determined from measurement and analysis of voltage-dependent charge movements.

机译：高亲和力兔Na（+）/葡萄糖共转运体SGLT1的过渡态，由电压依赖性电荷运动的测量和分析确定。

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摘要

The charge-membrane voltage (Q-V) distribution of wild-type rabbit Na(+)/glucose transporter (rSGLT1) expressed in Xenopus oocytes was investigated in the absence of glucose, using the two-electrode voltage-clamp technique. Although this distribution is generally believed to be well represented by a two-state Boltzmann equation, we recently provided evidence for the existence of at least four states (Krofchick D and Silverman M. Biophys J 84: 3690-3702, 2003), confirming an earlier finding for human SGLT1 (Chen XZ, Coady MJ, and Lapointe JY. Biophys J 71: 2544-2552, 1996). We now extend our study of rSGLT1 pre-steady-state currents, employing high-resolution measurement and analysis of the Q-V distribution. A ramp, instead of a step, voltage change was used to prevent saturation of the apparatus in the first approximately 1 ms. Transient currents were integrated out to 150 ms, instead of the standard 50-100 ms. Measurements were taken every 10 mV instead of the standard 20 mV. The Q-V distribution was fit with a two-, three-, and four-state Boltzmann equation and was described best by the three-state equation. The three-state fit produced two valences of 0.45 and 1.1 at two V(0.5) values of -48 and -7.7, respectively. Our findings are critically compared with other published studies and the differences are discussed. An implication of the three-state fit is that the turnover rate of rSGLT1 is 34 s(-1), i.e., 54% greater than previously reported (22 s(-1)). Our new findings support the concept that the sugar-free model of SGLT1 is more complex than generally accepted, most likely involving a minimum of four transition states.
机译：在非洲爪蟾卵母细胞中表达的野生型兔Na（+）/葡萄糖转运蛋白（rSGLT1）的电荷膜电压（Q-V）分布是在没有葡萄糖的情况下使用两电极电压钳技术研究的。尽管通常认为该分布可以很好地由两个状态的Boltzmann方程表示，但我们最近提供了至少存在四个状态的证据（Krofchick D和Silverman M. Biophys J 84：3690-3702，2003），人SGLT1的早期发现（Chen XZ，Coady MJ和Lapointe JY.Biophys J 71：2544-2552，1996）。现在，我们通过高分辨率测量和Q-V分布分析，扩展对rSGLT1前稳态电流的研究。使用斜坡而不是阶跃电压变化来防止设备在大约最初的1 ms内饱和。瞬态电流累计到150 ms，而不是标准的50-100 ms。每10 mV而不是标准20 mV进行测量。 Q-V分布与二态，三态和四态Boltzmann方程拟合，并且最好用三态方程来描述。三态拟合在两个V（0.5）值分别为-48和-7.7时产生两个化合价分别为0.45和1.1。我们的发现与其他已发表的研究进行了严格的比较，并对差异进行了讨论。三态拟合的含义是rSGLT1的周转率是34 s（-1），即比以前报告的（22 s（-1））高54％。我们的新发现支持以下概念：SGLT1的无糖模型比普遍接受的模型更为复杂，最有可能涉及至少四个过渡状态。

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