Fig. 3.
Roles of α-Kl and FGF23 in calcium homeostasis. α-Kl binds to Na+,K+-ATPase and regulates the recruitment of Na+,K+-ATPase to the cell surface membrane in response to lowered [Ca2+]o. α-Kl controls calcium re-absorption in the kidney DCT cells, calcium transportation across the choroid plexus into the CSF, and PTH secretion in the parathyroid glands. α-Kl is also involved in the signal transduction of Fgf23 that suppresses the gene expression of Cyp27b1 in the DCT nephrons that leads to negative regulation of 1,25(OH)2D3 synthesis. Calcium metabolism is governed by complicated reciprocal actions and feedback mechanisms and thus calcium concentrations in serum, body fluid and CSF are maintained within strictly narrow ranges.