Moran A, Handler J S, Turner R J
Am J Physiol. 1982 Nov;243(5):C293-8. doi: 10.1152/ajpcell.1982.243.5.C293.
Apical membrane vesicles were prepared from cultured epithelia formed by LLC-PK1 cells using a calcium precipitation technique. alpha-Methylglucoside uptake into this vesicle preparation was markedly stimulated by sodium and inhibited by phlorizin. In addition, a transient "overshoot" of intravesicular alpha-methylglucoside concentration above its equilibrium value was observed under initial sodium gradient conditions. The specificity of this sodium-dependent hexose transporter closely resembled that found in the mammalian kidney brush border membrane, e.g., alpha-methylglucoside, D-glucose, and D-galactose apparently share the transporter while 2-deoxy-D-glucose, mannose, and fructose do not. Kinetic analysis of the sodium-dependent component of alpha-methylglucoside flux into LLC-PK1 apical membrane vesicles indicates the existence of single transporter with Km congruent to 2 mM and Vmax congruent to 3 nmol.min-1.mg protein-1. Measurement of alpha-methylglucoside uptake as a function of sodium concentration is consistent with a sodium:sugar stoichiometry of approximately 2:1.l There is a good correlation over time between the development of the concentrating capacity of the intact epithelium for alpha-methylglucoside and the transport properties of the vesicle preparation.
采用钙沉淀技术从LLC - PK1细胞形成的培养上皮细胞中制备顶端膜囊泡。α - 甲基葡萄糖苷摄入该囊泡制剂的过程受到钠的显著刺激，并被根皮苷抑制。此外，在初始钠梯度条件下，观察到囊泡内α - 甲基葡萄糖苷浓度出现短暂的“过冲”，高于其平衡值。这种钠依赖性己糖转运体的特异性与在哺乳动物肾刷状缘膜中发现的特异性非常相似，例如，α - 甲基葡萄糖苷、D - 葡萄糖和D - 半乳糖显然共用该转运体，而2 - 脱氧 - D - 葡萄糖、甘露糖和果糖则不然。对α - 甲基葡萄糖苷流入LLC - PK1顶端膜囊泡的钠依赖性成分进行动力学分析表明，存在一种单一转运体，其Km约为2 mM，Vmax约为3 nmol·min⁻¹·mg蛋白⁻¹。将α - 甲基葡萄糖苷摄取量作为钠浓度的函数进行测量，结果与钠:糖化学计量比约为2:1一致。完整上皮细胞对α - 甲基葡萄糖苷的浓缩能力的发展与囊泡制剂的转运特性之间随时间存在良好的相关性。
