Hilden S, Sacktor B
Am J Physiol. 1982 Apr;242(4):F340-5. doi: 10.1152/ajprenal.1982.242.4.F340.
The uptake of D-glucose by renal brush border membrane vesicles was studied in the absence of Na+. Uptake of the sugar was membrane potential dependent (inside negative), inhibited by phlorizin, sugar and stereospecific, accelerated by exchange diffusion, saturable, and temperature dependent. The binding of phlorizin in the absence of Na+ was also increased by a membrane potential (inside negative). Thus, the properties of this membrane potential-dependent, Na+-independent sugar transport system resembled those described for the Na+-D-glucose cotransport system. In the absence of Na+ but in the presence of a valinomycin-induced K+ diffusion potential the apparent Km for D-glucose was 43 mM. This contrasted with an apparent Km of 1.8 mM for the Na+ chemical gradient system. Therefore, the Na+-independent uptake system represented a low-affinity transport mechanism. It is suggested that the same carrier mediated the Na+-independent and Na+-dependent transport systems. A hypothetical model for the membrane potential-dependent stimulation of D-glucose uptake in the absence of Na+ is proposed.
在无Na⁺的情况下研究了肾刷状缘膜囊泡对D-葡萄糖的摄取。糖的摄取依赖于膜电位（内膜为负），受根皮苷、糖抑制且具有立体特异性，通过交换扩散加速，具有饱和性且依赖于温度。在无Na⁺时根皮苷的结合也因膜电位（内膜为负）而增加。因此，这种依赖于膜电位、不依赖于Na⁺的糖转运系统的特性类似于描述的Na⁺-D-葡萄糖共转运系统。在无Na⁺但存在缬氨霉素诱导的K⁺扩散电位的情况下，D-葡萄糖的表观Km为43 mM。这与Na⁺化学梯度系统的表观Km 1.8 mM形成对比。因此，不依赖于Na⁺的摄取系统代表一种低亲和力转运机制。提示相同的载体介导不依赖于Na⁺和依赖于Na⁺的转运系统。提出了一个在无Na⁺情况下膜电位依赖性刺激D-葡萄糖摄取的假说模型。
