Walker J J, Yan T S, Quamme G A
Am J Physiol. 1987 Feb;252(2 Pt 2):F226-31. doi: 10.1152/ajprenal.1987.252.2.F226.
Renal brush-border membrane phosphate transport was studied in early and late segments of the pig proximal tubule. Vesicles were prepared from early proximal tubules (outer cortical tissue) and late proximal tubules (outer medullary tissue). Sodium-dependent phosphate uptake into brush-border membrane vesicles was determined using voltage clamp at 5-6 s, 21 degrees C. Sodium-dependent D-glucose uptake was determined to verify the cortical and medullary tissue cuts. At pH 8.0 (pHi = pHo), two sodium-dependent phosphate transport systems were evident in the early proximal tubule: a high-affinity system [Km, 0.06 +/- 0.01 mM; maximal transport activity (Vmax), 3.6 +/- 1.1 nmol X mg protein-1 X min-1] and a low-affinity system (Km, 4.11 +/- 0.02 mM; Vmax, 9.7 +/- 0.7 nmol X mg protein-1 X min-1). In the late proximal tubule at pH 8.0, only a single high-affinity transport process (Km, 0.19 +/- 0.7 mM; Vmax, 3.4 +/- 0.5 nmol X mg protein-1 X min-1) was evident. D-Glucose kinetics at pH 7.0 revealed both a high-affinity (Km, 0.55 +/- 0.09 mM) and a low-affinity (Km, 20.09 +/- 1.39 mM) system in the early proximal segment and a single high-affinity (Km, 1.27 +/- 0.36 mM) process in the late segment. These data suggest that two systems, distinct in their affinities and capacities, are involved in both D-glucose and phosphate transport across the brush-border membrane of the early proximal tubule, but that only a single high-affinity system is present in the late segment.
在猪近端小管的早期和晚期节段研究了肾刷状缘膜磷酸盐转运。囊泡取自早期近端小管（皮质外层组织）和晚期近端小管（髓质外层组织）。在5 - 6秒、21摄氏度下使用电压钳测定刷状缘膜囊泡中钠依赖性磷酸盐摄取。测定钠依赖性D - 葡萄糖摄取以验证皮质和髓质组织切片。在pH 8.0（细胞内pH = 细胞外pH）时，早期近端小管中有两个钠依赖性磷酸盐转运系统明显可见：一个高亲和力系统[米氏常数（Km），0.06±0.01 mM；最大转运活性（Vmax），3.6±1.1 nmol·mg蛋白⁻¹·min⁻¹]和一个低亲和力系统（Km，4.11±0.02 mM；Vmax，9.7±0.7 nmol·mg蛋白⁻¹·min⁻¹）。在pH 8.0时的晚期近端小管中，仅一个单一的高亲和力转运过程（Km，0.19±0.7 mM；Vmax，3.4±0.5 nmol·mg蛋白⁻¹·min⁻¹）明显可见。pH 7.0时D - 葡萄糖动力学显示，早期近端节段既有一个高亲和力（Km，0.55±0.09 mM）系统又有一个低亲和力（Km，20.09±1.39 mM）系统，而晚期节段只有一个单一的高亲和力（Km，1.27±0.36 mM）过程。这些数据表明，在早期近端小管的刷状缘膜上，D - 葡萄糖和磷酸盐转运涉及两个亲和力和容量不同的系统，但晚期节段仅存在一个单一的高亲和力系统。
