The primary reason for 1,25(OH)
The genomic actions of 1,25(OH)2 are mediated by the vitamin D receptor (VDR). 1,25(OH)2-occupied VDR heterodimerizes with the retinoid X receptor and together with co-regulatory proteins interacts with vitamin D response elements in and around target genes and mediates their transcription. 21,22
2 in the maintenance of calcium homeostasis is to increase calcium absorption from the intestine (Figure 1). 2 calcium absorption has been reported in the distal as well as the proximal intestine. 4 Rickets and osteomalacia are prevented when VDR null mice are fed a diet high in calcium and lactose, indicating that 1,25(OH)2 and VDR have a critical role in bone mineralization by regulating intestinal calcium absorption. 2step three,24 1,25(OH)2 has been reported to regulate every step of the intestinal transcellular calcium transport process. It induces the expression of the apical membrane calcium channel TRPV6, the calcium-binding protein calbindin-D9k (it has been suggested that calbindin facilitates, in part, translocation of calcium through the enterocyte and buffers calcium preventing toxic levels of calcium from accumulating in the cell), and the plasma membrane CaATPase, PMCA1b. Thereby, 1,25(OH)2 exerts its control in the intestine on calcium entry, calcium binding, and basolateral extrusion of calcium. 4
D3
When serum calcium is low, online dating Wichita 1,25(OH)2 and parathyroid hormone (PTH) act to maintain calcium homeostasis. 1,25(OH)2-the active form of vitamin D and the ligand for the vitamin D receptor (VDR)-acts to increase calcium absorption from the intestine. If normal calcium is unable to be maintained by intestinal calcium absorption, then 1,25(OH)2 and PTH, together acting via their receptors, release calcium from the bone stores and increase reabsorption of calcium from the distal tubule of the kidney.