title: Magnesium stimulates renal phosphate reabsorption.
abstract: In the kidney, approximately 80% of the filtered phosphate (Pi) is reabsorbed along the proximal tubule. Changes in renal Pi reabsorption are associated with modulation of the sodium-dependent Pi 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 Pi 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 Pi handling. Urinary Pi 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 Pi 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 Pi 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 Pi 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 Pi 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.
authors.affiliation: Department of Pediatric Nephrology, Charité University Children's Hospital, Augustenburger Platz 1, 13353 Berlin, Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Thumfart
authors.forename: Susanne
authors.initials: S
authors.lastname: Jung
authors.forename: Salah
authors.initials: S
authors.lastname: Amasheh
authors.forename: Stephanie
authors.initials: S
authors.lastname: Krämer
authors.forename: Harm
authors.initials: H
authors.lastname: Peters
authors.forename: Kerstin
authors.initials: K
authors.lastname: Sommer
authors.forename: Jürg
authors.initials: J
authors.lastname: Biber
authors.forename: Heini
authors.initials: H
authors.lastname: Murer
authors.forename: Iwan
authors.initials: I
authors.lastname: Meij
authors.forename: Uwe
authors.initials: U
authors.lastname: Querfeld
authors.forename: Carsten A
authors.initials: CA
authors.lastname: Wagner
authors.forename: Dominik
authors.initials: D
authors.lastname: Müller
mesh_terms: D000821:Animal Feed; D000818:Animals; D005346:Fibroblast Growth Factors / Q000097:blood; D007150:Immunohistochemistry; D007668:Kidney / Q000378:metabolism*; D008041:Linoleic Acids / Q000097:blood; D008274:Magnesium / Q000494:pharmacology*; D008297:Male; D010281:Parathyroid Hormone / Q000097:blood; D016105:Parathyroidectomy; D010710:Phosphates / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D050613:Sodium-Phosphate Cotransporter Proteins, Type IIa / Q000235:genetics / Q000378:metabolism*; D050615:Sodium-Phosphate Cotransporter Proteins, Type IIc / Q000235:genetics / Q000378:metabolism*; D017965:gamma-Linolenic Acid / Q000097:blood
chemical_list: C505605:Fgf23 protein, rat; D008041:Linoleic Acids; D010281:Parathyroid Hormone; D010710:Phosphates; D012333:RNA, Messenger; C493556:Slc34a1 protein, rat; C493564:Slc34a3 protein, rat; D050613:Sodium-Phosphate Cotransporter Proteins, Type IIa; D050615:Sodium-Phosphate Cotransporter Proteins, Type IIc; C090557:So 1100; D005346:Fibroblast Growth Factors; D017965:gamma-Linolenic Acid; D008274:Magnesium