Skip to main content
. 2015 Dec 16;96(1):365–408. doi: 10.1152/physrev.00014.2015

Figure 5.

Figure 5.

Renal VDR actions. In the proximal tubule cells, CYP27B1 expression is suppressed by 1,25(OH)2D3 and FGF23. FGF23 also stimulates phosphate excretion by decreasing the expression of the phosphate transporters NPT2a/c in the apical membrane. FGF23 may signal by binding to the few FGFR1-Klotho complexes in the proximal tubules or by inducing a paracrine factor (factor X) in the distal tubules where abundant FGFR1-Klotho complexes are present. Renal calcium reabsorption in the distal tubule is stimulated by 1,25(OH)2D3. 1,25(OH)2D3 increases the expression of calbindin-D9k and calbindin-D28k and to a lesser extent of TRPV5. The extrusion of calcium at the basolateral side is mediated by PMCA1b and NCX1. Two models are proposed on how Klotho and FGF23 regulate TRPV5 expression: 1) secreted Klotho (sKlotho) is considered to hydrolyze sugar residues from the glycan chains on TRPV5 resulting in better entrapment of TRPV5 in the apical membrane; and 2) FGF23 binds to the basolateral FGFR1-Klotho complex, which stimulates intracellular transport of TRPV5 to the plasma membrane.