Chambard J-M, Ashmore J F
Department of Physiology, University College London, UK.
J Physiol. 2003 Aug 1;550(Pt 3):667-77. doi: 10.1113/jphysiol.2003.039321.
The mammalian cochlea contains a population of outer hair cells (OHCs) whose electromotility depends on an assembly of 'motor' molecules in the basolateral membrane of the cell. Named 'prestin', the molecule is a member of the SLC26 anion transporter superfamily. We show both directly and indirectly that SLC26A5, rat prestin, takes up hexoses when expressed in several cell lines. Direct measurements of labelled fructose transport into COS-7 cells expressing prestin are reported here. Indirect measurements, using imaging techniques, show that transfected HEK-293 or CHO-Ki cells undergo reversible volume changes when exposed to isosmotic glucose-fructose exchange. The observations are consistent with the sugar transport. A similar transport was observed using a C-terminal green fluorescent protein (GFP)-tagged pendrin (SLC26A4) construct. Cells transfected with GFP alone did not respond to sugars. The data are consistent with fructose being transported by prestin with an apparent Km=24 nm. From the voltage-dependent capacitance of transfected cells, we estimate that 250,000 prestin molecules were present and hence that the single transport rate is not more than 3000 fructose molecules s(-1). Comparison of the transfected cell swelling rates induced by fructose and by osmotic steps indicates that water was co-transported with sugar. We suggest that the structure of SLC26 family members allows them to act as neutral substrate transporters and may explain observed properties of cochlear hair cells.
哺乳动物的耳蜗含有一群外毛细胞（OHC），其电运动性取决于细胞基底外侧膜中“马达”分子的组装。该分子名为“prestin”，是SLC26阴离子转运体超家族的成员。我们直接和间接表明，大鼠prestin即SLC26A5，在几种细胞系中表达时能摄取己糖。本文报道了对标记果糖转运到表达prestin的COS-7细胞中的直接测量。使用成像技术的间接测量表明，转染的HEK-293或CHO-Ki细胞在暴露于等渗葡萄糖-果糖交换时会发生可逆的体积变化。这些观察结果与糖转运一致。使用C端绿色荧光蛋白（GFP）标记的pendrin（SLC26A4）构建体也观察到了类似的转运。仅转染GFP的细胞对糖无反应。数据表明果糖由prestin转运，其表观Km = 24 nm。根据转染细胞的电压依赖性电容，我们估计存在250,000个prestin分子，因此单次转运速率不超过3000个果糖分子·秒⁻¹。比较果糖和渗透步骤诱导的转染细胞肿胀速率表明水与糖共转运。我们认为SLC26家族成员的结构使其能够作为中性底物转运体，并可能解释耳蜗毛细胞的观察特性。
