Department of Nutrition, Food Science and Physiology, University of Navarra, Pamplona, Spain.
J Physiol Biochem. 2013 Sep;69(3):507-12. doi: 10.1007/s13105-013-0239-6. Epub 2013 Jan 30.
Leptin is secreted by gastric mucosa and is able to reach the intestinal lumen where its receptors are located in the apical membrane of the enterocytes. We have previously demonstrated that apical leptin inhibits sugar and amino acids uptake in vitro and glucose absorption in vivo. Since leptin receptors are also expressed in the basolateral membrane of the enterocytes, the aim of the present work was to investigate whether leptin acting from the basolateral side could also regulate amino acid uptake. Tritiated Gln and β-Ala were used to measure uptake into Caco-2 cells grown on filters, in the presence of basal leptin at short incubation times (5 and 30 min) and after 6 h of preincubation with the hormone. In order to compare apical and basal leptin effect, Gln and β-Ala uptake was measured in the presence of leptin acting from the apical membrane also in cells grown on filters. Basal leptin (8 mM) inhibited by ~15-30% the uptake of 0.1 mM Gln and 1 mM β-Ala quickly, after 5 min exposure, and the effect was maintained after long preincubation periods. Apical leptin had the same effect. Moreover, the inhibition was rapidly and completely reversed when leptin was removed from the apical or basolateral medium. These results extend our previous findings and contribute to the vision of leptin as an important hormonal signal for the regulation of intestinal absorption of nutrients.
瘦素由胃黏膜分泌，能够到达肠道腔，其受体位于肠上皮细胞的顶膜上。我们之前已经证明，顶膜上的瘦素抑制体外糖和氨基酸的摄取以及体内葡萄糖的吸收。由于瘦素受体也在肠上皮细胞的基底外侧膜上表达，因此本研究的目的是研究从基底外侧作用的瘦素是否也可以调节氨基酸摄取。氚标记的 Gln 和 β-Ala 用于测量在存在基础瘦素的情况下，在短孵育时间（5 和 30 分钟）和用激素预孵育 6 小时后，在滤器上生长的 Caco-2 细胞中的摄取。为了比较顶膜和基底膜上瘦素的作用，还在滤器上生长的细胞中测量了从顶膜作用的瘦素对 Gln 和 β-Ala 摄取的影响。基础瘦素（8 mM）在 5 分钟暴露后迅速抑制 0.1 mM Gln 和 1 mM β-Ala 的摄取约 15-30％，并且在长时间预孵育后仍保持该作用。顶膜上的瘦素也有相同的作用。此外，当从顶膜或基底外侧介质中去除瘦素时，抑制作用迅速而完全逆转。这些结果扩展了我们之前的发现，并有助于将瘦素视为调节肠道营养吸收的重要激素信号。
