VOLTAGE-CLAMP STUDIES OF THE NA+/GLUCOSE COTRANSPORTER CLONED FROM RABBIT SMALL-INTESTINE
VOLTAGE-CLAMP STUDIES OF THE NA+/GLUCOSE COTRANSPORTER CLONED FROM RABBIT SMALL-INTESTINE
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DOI：
10.1007/bf00370455
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发表时间：
1991-03-01
影响因子：
4.5
通讯作者：
WRIGHT, EM
中科院分区：
文献类型：
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作者：
BIRNIR, B;LOO, DDF;WRIGHT, EM
用双微电极电压钳方法研究了爪蟾卵母细胞表达的肠钠/葡萄糖协同转运蛋白的内向钠电流。 稳态电流/电压关系显示电压依赖性（V（m）从+20 mV到-75 mV）和相对电压无关性（V（m）从-75 mV到-150 mV）区域。 Na+和葡萄糖的表观I（max）随膜电位负移而增加，葡萄糖的表观K_（0.5）（K_（0.5）Glc）依赖于V（m）和[Na]_o。 将[Na]o从7增加到110 mmol/l，在将K0.5Glc从0.44降低到0.03 mmol/l方面具有与将V（m）从-40增加到-150 mV相同的效果。 在饱和条件下（20 mmol/l外部糖和110 mmol/l [Na]o），D-葡萄糖、D-半乳糖、α-甲基D-吡喃葡萄糖苷和3-O-甲基D-葡萄糖苷的I/V曲线相同。 对糖的特异性顺序为：D-葡萄糖、D-半乳糖、α-甲基D-吡喃葡萄糖苷> 3-O-甲基D-葡萄糖苷>> D-木糖> D-阿洛糖>> D-甘露糖。 根皮苷（几乎等于10 μ mol/l）的K（i）在饱和[Na]o时与V（m）无关。 我们的结论是，各种糖的运输由克隆的Na+/葡萄糖协同转运蛋白在相同的最大速率和膜电位影响的最大电流和表观K0.5的Na+和葡萄糖的协同转运蛋白。
Inward Na+ currents associated with the cloned intestinal Na+/glucose cotransporter expressed in Xenopus oocytes have been studied using the two-microeletrode voltage-clamp method. The steady-state current/voltage relations showed voltage-dependent (V(m) from +20 to -75 mV) and relatively voltage-independent (V(m) from -75 to -150 mV) regions. The apparent I(max) for Na+ and glucose increased with negative membrane potentials, and the apparent K0.5 for glucose (K0.5Glc) depended on V(m) and [Na]o. Increasing [Na]o from 7 to 110 mmol/l had the same effect in decreasing K0.5Glc from 0.44 to 0.03 mmol/l as increasing the V(m) from -40 to -150 mV. The I/V curves under saturating conditions (20 mmol/l external sugars and 110 mmol/l [Na]o) were identical for D-glucose, D-galactose, alpha-methyl D-glucopyranoside and 3-O-methyl D-glucoside. The specificity of the cotransporter for sugars was: D-glucose, D-galactose, alpha-methyl D-glucopyranoside > 3-O-methyl D-glucoside >> D-xylose > D-allose >> D-mannose. K(i) for phlorizin (almost-equal-to 10-mu-mol/l) was independent of V(m) at saturating [Na]o. We conclude that a variety of sugars are transported by the cloned Na+/glucose cotransporter at the same maximal rate and that membrane potential affects both the maximal current and the apparent K0.5 of the cotransporter for Na+ and glucose.