Chen M L, King R S, Armbrecht H J
Veterans Administration Medical Center, St. Louis, Missouri 63125.
J Cell Physiol. 1990 Jun;143(3):488-93. doi: 10.1002/jcp.1041430313.
The transport of phosphate by primary cultures of renal cells from young (5-6 weeks) and adult (10-12 months) rats was studied. Renal tubule cells isolated from young and adult groups exhibited typical epithelial morphology and similar growth rates. The Na-dependent phosphate uptake was saturable with a Km of 5-7 microM over a substrate range of 1-500 microM. A decrease in Na-dependent phosphate uptake in adult cells (30%) was found compared to that of young cells. The Na-independent component of phosphate uptake did not vary with age. In addition, the inhibition of phosphate uptake by a variety of compounds (ouabain, gramicidin, 2,4-dinitrophenol, KCN, and arsenate) were similar in both age groups. Kinetic analysis showed that a significant reduction in Vmax (4.4 +/- 0.4 vs. 3.1 +/- 0.2 nmol Pi/mg protein/10 min in young and adult cells, respectively), but not Km, resulted in this decreased uptake of phosphate in adult groups. There was no difference in the efflux of phosphate from both age groups. When cells were preincubated in a phosphate-free medium for 24 hours, the uptake of phosphate was increased to 46% and 24% of their corresponding controls in young and adult cells, respectively. The decreased phosphate uptake and limited adaptation to a phosphate-free medium by the adult renal cells may account for the hypophosphatemia and phosphaturia seen in adult and old animals in vivo.
研究了幼年（5 - 6周）和成年（10 - 12个月）大鼠肾细胞原代培养物对磷酸盐的转运。从幼年组和成年组分离出的肾小管细胞呈现典型的上皮形态且生长速率相似。在1 - 500微摩尔的底物范围内，钠依赖性磷酸盐摄取具有饱和性，其米氏常数（Km）为5 - 7微摩尔。与幼年细胞相比，发现成年细胞中钠依赖性磷酸盐摄取减少了30%。磷酸盐摄取的非钠依赖性成分不随年龄变化。此外，在两个年龄组中，多种化合物（哇巴因、短杆菌肽、2,4 - 二硝基苯酚、氰化钾和砷酸盐）对磷酸盐摄取的抑制作用相似。动力学分析表明，成年组磷酸盐摄取减少是由于最大反应速度（Vmax）显著降低（幼年和成年细胞分别为4.4±0.4和3.1±0.2纳摩尔磷酸根/毫克蛋白质/10分钟），而米氏常数（Km）没有变化。两个年龄组的磷酸盐流出没有差异。当细胞在无磷酸盐培养基中预孵育24小时时，幼年和成年细胞中磷酸盐摄取分别增加到其相应对照组的46%和24%。成年肾细胞中磷酸盐摄取减少以及对无磷酸盐培养基的适应性有限，可能是成年和老年动物体内低磷血症和磷尿症的原因。
