Institute for Physiology and Cell Biology, University of Veterinary Medicine Hannover, 30173 Hannover, Germany.
Int J Mol Sci. 2021 Jan 16;22(2):866. doi: 10.3390/ijms22020866.
The intestinal absorption of phosphate (P) takes place transcellularly through the active NaPi-cotransporters type IIb (NaPiIIb) and III (PiT1 and PiT2) and paracellularly by diffusion through tight junction (TJ) proteins. The localisation along the intestines and the regulation of P absorption differ between species and are not fully understood. It is known that 1,25-dihydroxy-vitamin D (1,25-(OH)D) and phosphorus (P) depletion modulate intestinal P absorption in vertebrates in different ways. In addition to the apical uptake into the enterocytes, there are uncertainties regarding the basolateral excretion of P. Functional ex vivo experiments in Ussing chambers and molecular studies of small intestinal epithelia were carried out on P-deficient goats in order to elucidate the transepithelial P route in the intestine as well as the underlying mechanisms of its regulation and the proteins, which may be involved. The dietary P reduction had no effect on the duodenal and ileal P transport rate in growing goats. The ileal PiT1 and PiT2 mRNA expressions increased significantly, while the ileal PiT1 protein expression, the mid jejunal claudin-2 mRNA expression and the serum 1,25-(OH)D levels were significantly reduced. These results advance the state of knowledge concerning the complex mechanisms of the P homeostasis in vertebrates.
肠对磷酸盐（P）的吸收是通过主动 NaPi 共转运蛋白 IIb（NaPiIIb）和 III（PiT1 和 PiT2）经细胞途径进行的，通过紧密连接（TJ）蛋白经细胞旁扩散进行。P 吸收在不同物种中的局部定位和调节方式不同，目前尚未完全了解。已知 1,25-二羟维生素 D（1,25-(OH)D）和磷（P）耗竭以不同的方式调节脊椎动物的肠道 P 吸收。除了顶端进入肠细胞外，P 的基底外侧排泄也存在不确定性。在 P 缺乏的山羊中进行 Ussing 室的功能离体实验和小肠上皮的分子研究，以阐明肠上皮细胞的跨上皮 P 途径及其调节的潜在机制以及可能涉及的蛋白质。在生长山羊中，饮食 P 减少对空肠和回肠 P 转运速率没有影响。回肠 PiT1 和 PiT2 mRNA 表达显著增加，而回肠 PiT1 蛋白表达、中肠闭合蛋白-2 mRNA 表达和血清 1,25-(OH)D 水平显著降低。这些结果推进了关于脊椎动物 P 动态平衡的复杂机制的知识状态。
