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This Article Full Text Full Text (PDF) All Versions of this Article: 295/4/F1126    most recent 00353.2007v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Thumfart, J. Articles by Müller, D. Search for Related Content PubMed PubMed Citation Articles by Thumfart, J. Articles by Müller, D.

Magnesium stimulates renal phosphate reabsorption

¹Department of Pediatric Nephrology, Charité University Children's Hospital, Departments of ²Clinical Physiology and ³Nephrology, Charité University Hospital, Berlin; ⁴Institute of Physiology and Zurich Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland; and ⁵Max-Delbrueck-Centre for Molecular Medicine, Berlin, Germany

Submitted 31 July 2007 ; accepted in final form 1 August 2008

In the kidney, 80% of the filtered phosphate (P_i) is reabsorbed along the proximal tubule. Changes in renal P_i reabsorption are associated with modulation of the sodium-dependent P_i cotransporter type IIa (NaPi-IIa) and type IIc (NaPi-IIc) protein abundance in the brush-border membrane (BBM) of proximal tubule cells. NaPi-IIa is mainly regulated by dietary P_i intake and parathyroid hormone (PTH). The purpose of the present study was to elucidate the effect of alteration in dietary magnesium (Mg²⁺) intake on renal P_i handling. Urinary P_i excretion and renal expression of NaPi-IIa and NaPi-IIc were analyzed in rats fed a normal (0.2%) or high-Mg²⁺ (2.5%) diet. A high-Mg²⁺ diet resulted in decreased renal P_i excretion and increased protein expression of NaPi-IIa and NaPi-IIc. Serum FGF-23 (fibroblast growth factor 23) levels were unchanged under a high-Mg²⁺ diet. Serum PTH levels were slightly decreased under a high-Mg²⁺ diet. To examine whether the observed changes in renal P_i reabsorption are PTH dependent, expression of NaPi-IIa and NaPi-IIc was also analyzed in parathyroidectomized (PTX) rats fed a normal or high-Mg²⁺ diet. In PTX rats, Mg²⁺ had no significant effect on renal P_i excretion or NaPi-IIa protein expression. Mg²⁺ increased NaPi-IIc protein expression in PTX rats. This experiment shows for the first time on the molecular level how Mg²⁺ stimulates renal P_i reabsorption. Under a high-Mg²⁺ diet, NaPi-IIa expression is dependent on PTH levels, whereas NaPi-IIc expression seems to be independent of PTH levels.

parathyroid hormone