ONTOGENY OF INTESTINAL PHOSPHATE ABSORPTION IN RABBITS
ONTOGENY OF INTESTINAL PHOSPHATE ABSORPTION IN RABBITS
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DOI：
10.1152/ajpgi.1992.262.5.g847
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发表时间：
1992-05-01
影响因子：
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通讯作者：
GRANRUD, GS
中科院分区：
文献类型：
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作者：
BOROWITZ, SM;GRANRUD, GS
用2周龄、4周龄、6周龄和3个月龄兔制备的刷状缘膜囊泡，观察肠道磷酸盐转运的个体发育。在所有四个年龄段，从十二指肠制备的囊泡都显示出钠磷共转运，在钠梯度存在的情况下摄取明显大于在钾梯度存在的情况下摄取。虽然钠非依赖性磷酸盐摄取量在所有年龄段都是相似的，但钠-磷酸盐共转运在最年轻的动物中最大，并随着年龄的增长而下降。在2wk时，磷吸收峰值是平衡值的10倍，而成年人下降到平衡值的3倍。钠磷共转运的最大转运能力从2wk时的2292+/-161wk降至3mo时的286+/-12pmol.mg-1.10 S-1，而米氏常数在0.032~0.054 mm之间变化不大。在所有年龄段，摄取在30-50 mM钠之间达到一半最大刺激，Hill系数在1.5-2之间。在任何年龄段，内负扩散电位的产生并不显著地促进磷的吸收。这些数据表明，在整个发育过程中，每个磷酸盐分子通过兔十二指肠刷状缘膜的运输与两个钠分子的运输是耦合的。钠磷共转运在肠段的分布有明显的发育性变化。在2周龄的动物中，钠-磷酸共转运存在于十二指肠、近端和远端空肠以及近端回肠。在4周龄动物中，钠磷共转运存在于整个十二指肠以及近端和远端空肠中，而在6周和12周龄动物中，仅在十二指肠和近端空肠中观察到钠磷共转运。
The ontogeny of intestinal phosphate transport was examined in brush-border membrane vesicles prepared from 2-wk, 4-wk, 6-wk, and 3-mo-old rabbits. At all four ages, vesicles prepared from the duodenum demonstrated sodium-phosphate cotransport in that uptake in the presence of a sodium gradient was significantly greater than uptake in the presence of a potassium gradient. While sodium-independent phosphate uptake was comparable at all ages, sodium-phosphate cotransport was greatest in the youngest animals and declined with increasing age. Peak phosphate uptake was 10-fold the equilibrium value at 2 wk and declined to 3-fold in adults. Maximal transport capacity of sodium-phosphate cotransport fell from 2,292 +/- 161 at 2 wk to 286 +/- 12 pmol.mg-1.10 s-1 at 3 mo, whereas the Michaelis constant did not change with age, varying between 0.032 and 0.054 mM. At all ages, uptake was half-maximally stimulated between 30 and 50 mM sodium, and Hill coefficients were between 1.5 and 2. Generation of inside negative diffusion potentials did not significantly enhance phosphate uptake at any age. These data suggest that throughout development, the transport of each phosphate molecule across the rabbit duodenal brush-border membrane is coupled to the transport of two sodium molecules. There were distinct developmental changes in the distribution of the sodium-phosphate cotransport along the length of intestine. In 2-wk old animals, sodium-phosphate cotransport was present in the duodenum, proximal and distal jejunum, and proximal ileum. In 4-wk-old animals, sodium-phosphate cotransport was present throughout the duodenum and proximal and distal jejunum, and in 6-wk and 12-wk-old animals, sodium-phosphate cotransport was observed only in the duodenum and proximal jejunum.