Slayman C L, Slayman C W
Proc Natl Acad Sci U S A. 1974 May;71(5):1935-9. doi: 10.1073/pnas.71.5.1935.
Intracellular microelectrodes were used to measure the effects of glucose transport on membrane voltage and membrane resistance in Neurospora crassa. Sudden activation of glucose uptake, via the high-affinity, derepressible system II, results in a very large depolarization of the plasma membrane. At saturating concentrations of glucose, the depolarization averages 120 mV; it is diphasic in time, with an initial shift at rates of 100-200 mV/sec followed by a slow, spontaneous, partial repolarization. Changes in intracellular ATP concentration are small and could account for only 10 mV of the initial depolarization, while the rest appears to depend upon the transport process itself. A plot of peak depolarization against the extracellular glucose concentration gives a saturation curve which is half-maximal at 42 muM, in good agreement with the K(1/2) reported for glucose transport via system II. The nonmetabolized analogue 3-O-methyl-D-glucose also causes depolarization, and in addition leads to a pulsed alkalinization of the medium occurring at approximately the same rate as 3-O-methyl-D-glucose uptake. The membrane resistance falls only slightly during glucose depolarization, a fact which requires the transport system itself to have a high internal resistance, or the membrane current-voltage relationship in glucose-starved cells to be quite nonlinear. All of the data support Mitchell's notion that sugar and hydrogen ions are contransported under the influence of the membrane potential, and lead to values for H(+):glucose stoichiometry of 0.8 to 1.4.
利用细胞内微电极来测量葡萄糖转运对粗糙脉孢菌细胞膜电压和膜电阻的影响。通过高亲和力、可去阻遏的转运系统II突然激活葡萄糖摄取，会导致质膜发生非常大的去极化。在葡萄糖饱和浓度下，去极化平均为120 mV；其在时间上呈双相性，初始变化速率为100 - 200 mV/秒，随后是缓慢的、自发的部分复极化。细胞内ATP浓度的变化很小，仅能解释初始去极化的10 mV，而其余部分似乎取决于转运过程本身。将峰值去极化与细胞外葡萄糖浓度作图得到一条饱和曲线，其在42 μM时达到半最大值，这与报道的通过转运系统II进行葡萄糖转运的K(1/2)值非常一致。非代谢类似物3 - O - 甲基 - D - 葡萄糖也会引起去极化，此外还会导致培养基以与3 - O - 甲基 - D - 葡萄糖摄取大致相同的速率发生脉冲式碱化。在葡萄糖去极化过程中膜电阻仅略有下降，这一事实要求转运系统本身具有高内阻，或者葡萄糖饥饿细胞中的膜电流 - 电压关系相当非线性。所有数据都支持米切尔的观点，即糖和氢离子在膜电位的影响下协同转运，并且得出H(+)：葡萄糖化学计量比为0.8至1.4。
