Intestinal and renal adaptation to a low-Pi diet of type II NaPi cotransporters in vitamin D receptor- and 1alphaOHase-deficient mice |
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Authors: | Capuano Paola Radanovic Tamara Wagner Carsten A Bacic Desa Kato Shigeaki Uchiyama Yasushi St-Arnoud René Murer Heini Biber Jürg |
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Institution: | Institute of Physiology, University of Zurich, Zurich, Switzerland. |
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Abstract: | Intake of a low-phosphate diet stimulates transepithelial transport of Pi in small intestine as well as in renal proximal tubules. In both organs, this is paralleled by a change in the abundance of the apically localized NaPi cotransporters NaPi type IIa (NaPi-IIa) and NaPi type IIb (NaPi-IIb), respectively. Low-Pi diet, via stimulation of the activity of the renal 25-hydroxyvitamin-D3-1 -hydroxylase (1 OHase), leads to an increase in the level of 1,25-dihydroxy-vitamin D3 1,25(OH)2D]. Regulation of the intestinal absorption of Pi and the abundance of NaPi-IIb by 1,25(OH)2D has been supposed to involve the vitamin D receptor (VDR). In this study, we investigated the adaptation to a low-Pi diet of NaPi-IIb in small intestine as well as NaPi-IIa in kidneys of either VDR- or 1 OHase-deficient mice. In both mouse models, upregulation by a low-Pi diet of the NaPi cotransporters NaPi-IIa and NaPi-IIb was normal, i.e., similar to that observed in the wild types. Also, in small intestines of VDR- and 1 OHase-deficient mice, the same changes in NaPi-IIb mRNA found in wild-type mice were observed. On the basis of the results, we conclude that the regulation of NaPi cotransport in small intestine (via NaPi-IIb) and kidney (via NaPi-IIa) by low dietary intake of Pi cannot be explained by the 1,25(OH)2D-VDR axis. NaPi type IIb; vitamin D3 |
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