[New aspect of renal phosphate reabsorption and phosphate metabolism]

Abnormalities of the inorganic phosphate (Pi) reabsorption in the kidney result in various disorders. Na(+)-dependent Pi (NaPi) transporters (NaPi- II a and NaPi- II c) in the brush border membrane of proximal tubular cells mediate the rate-limiting step in the overall Pi-reabsorptive process. The PTH (parathyroid hormone) -induced inhibition of Pi reabsorption is mediated by endocytosis of the NaPi- II a transporter from brush border membrane. NaPi- II a is part of the heteromeric protein complexes organized by PDZ ( [PSD-95/Disc-large/ZO-1] -binding proteins) proteins. The NaPi- II c transporter is also regulated by PTH via internalization, but by a vesicular transport pathway distinct from that used by the NaPi- II a transporter. In addition, the importance of the fibrobalst growth factor 23 (FGF23) -klotho axis in regulating mineral ion homeostasis. We will summarize how the FGF23-klotho might regulate renal Pi reabsorption.