KINETICS OF STEADY-STATE CURRENTS AND CHARGE MOVEMENTS ASSOCIATED WITH THE RAT NA+/GLUCOSE COTRANSPORTER
KINETICS OF STEADY-STATE CURRENTS AND CHARGE MOVEMENTS ASSOCIATED WITH THE RAT NA+/GLUCOSE COTRANSPORTER
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DOI：
10.1074/jbc.270.45.27099
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发表时间：
1995-11-10
影响因子：
4.8
通讯作者：
WRIGHT, EM
中科院分区：
文献类型：
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作者：
PANAYOTOVAHEIERMANN, M;LOO, DDF;WRIGHT, EM
大鼠Na+/葡萄糖协同转运蛋白（SGLT 1）在非洲爪蟾卵母细胞中表达，并使用双电极电压钳测量稳态和瞬态电流。葡萄糖诱导的最大钠依赖性内向电流约为300-500 nA。（α-甲基-D-吡喃葡萄糖苷; a千年发展目标）（K-0.5（α MDG））钠（K-0.5（Na））在-150 mV的膜电位下的浓度为0.2 mM和4 mM。（0.5）随着去极化电位在-30 mV达到40 mM而连续增加，K-0.5（α MDG）是急剧电压依赖性的，在-30 mV为0.46 mM，在-10 mV为1 mM。在所有测试的单价阳离子中，只有Li+可以取代Na+，但亲和力较低，相对底物特异性为D-葡萄糖> α MDG接近D-半乳糖> 3-O-Me-Glc远大于β-萘基-D-葡萄糖苷远大于尿苷，根皮苷（Pt），糖转运的特异性阻断剂，对大鼠协同转运蛋白显示出极高的亲和力，抑制剂常数（Ki（Pz））为12 nM。通过Boltzmann方程拟合不存在糖时的SGLT 1电荷移动，可移动电荷的表观价态类似于1，即50%最大电荷转移的电位（V-0.5）为-43 mV，最大电荷（Q（max））为9纳库仑，大鼠SGLT 1的表观转换数为30 s（-1），模型模拟表明，大鼠SGLT 1的动力学描述的六状态有序非快速平衡模型，和大鼠，兔和人的协同转运蛋白的动力学的比较表明，他们主要在其稳态前的动力学参数不同。
The rat Na+/glucose cotransporter (SGLT1) was expressed in Xenopus oocytes and steady-state and transient currents were measured using a two-electrode voltage clamp. The maximal glucose induced Na+-dependent inward current was similar to 300-500 nA, The apparent affinity constants for sugar (alpha-methyl-D-glucopyrano-side; alpha MDG) (K-0.5(alpha MDG)) sodium (K-0.5(Na)) at a membrane potential of -150 mV were 0.2 mM and 4 mM. The (Na)(0.5) increased continuously with depolarizing potentials reaching 40 mM at -30 mV, K-0.5(alpha MDG) was steeply voltage dependent, 0.46 mM at -30 mV and 1 mM at -10 mV. From all tested monovalent cations only Li+ could substitute for Na+ but with lower affinity, The relative substrate specificity was D-glucose > alpha MDG approximate to D-galactose > 3-O-Me-Glc much greater than beta-naphthyl-D-glucoside much greater than uridine, Phlorizin (Pt), the specific blocker of sugar transport, showed an extremely high affinity for the rat cotransporter with an inhibitor constant (K-i(Pz)) of 12 nM. SGLT1 charge movements in the absence of sugar were fitted by the Boltzmann equation with an apparent valence of the movable charge of similar to 1, a potential for 50% maximal charge transfer (V-0.5) of -43 mV, and a maximal charge (Q(max)) of 9 nanocoulombs, The apparent turnover number for the rat SGLT1 was 30 s(-1), Model simulations showed that the kinetics of the rat SGLT1 are described by a six-state ordered nonrapid equilibrium model, and comparison of the kinetics of the rat, rabbit and human cotransporters indicate that they differ mainly in their presteady-state kinetic parameters.