Beschreibung:
<jats:p>In the kidney, ∼80% of the filtered phosphate (P<jats:sub>i</jats:sub>) is reabsorbed along the proximal tubule. Changes in renal P<jats:sub>i</jats:sub>reabsorption are associated with modulation of the sodium-dependent P<jats:sub>i</jats:sub>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<jats:sub>i</jats:sub>intake and parathyroid hormone (PTH). The purpose of the present study was to elucidate the effect of alteration in dietary magnesium (Mg<jats:sup>2+</jats:sup>) intake on renal P<jats:sub>i</jats:sub>handling. Urinary P<jats:sub>i</jats:sub>excretion and renal expression of NaPi-IIa and NaPi-IIc were analyzed in rats fed a normal (0.2%) or high-Mg<jats:sup>2+</jats:sup>(2.5%) diet. A high-Mg<jats:sup>2+</jats:sup>diet resulted in decreased renal P<jats:sub>i</jats:sub>excretion and increased protein expression of NaPi-IIa and NaPi-IIc. Serum FGF-23 (fibroblast growth factor 23) levels were unchanged under a high-Mg<jats:sup>2+</jats:sup>diet. Serum PTH levels were slightly decreased under a high-Mg<jats:sup>2+</jats:sup>diet. To examine whether the observed changes in renal P<jats:sub>i</jats:sub>reabsorption are PTH dependent, expression of NaPi-IIa and NaPi-IIc was also analyzed in parathyroidectomized (PTX) rats fed a normal or high-Mg<jats:sup>2+</jats:sup>diet. In PTX rats, Mg<jats:sup>2+</jats:sup>had no significant effect on renal P<jats:sub>i</jats:sub>excretion or NaPi-IIa protein expression. Mg<jats:sup>2+</jats:sup>increased NaPi-IIc protein expression in PTX rats. This experiment shows for the first time on the molecular level how Mg<jats:sup>2+</jats:sup>stimulates renal P<jats:sub>i</jats:sub>reabsorption. Under a high-Mg<jats:sup>2+</jats:sup>diet, NaPi-IIa expression is dependent on PTH levels, whereas NaPi-IIc expression seems to be independent of PTH levels.</jats:p>