Cellular mechanisms in proximal tubular handling of phosphate

: In the kidney, reabsorption of filtered inorganic phosphate (Pi) takes place along the proximal tubules and is controlled by a variety of hormones (e.g.parathyroid hormone, PTH). Three structurally unrelated sodium-dependent phosphate (Na/Pi) cotransporter families have been identified. Targeted inactivation of the type IIa Na/Pi cotransporter gene (npt2) provided strong evidence that - 70% of Na-dependent Pi transport across the brush border membrane is mediated by the type IIa Na/Pi cotransporter. The type IIa cotransporter represents the major target for PTH. The type IIa cotransporter interacts with various PDZ proteins that might be responsible for the apical sorting, PTH controlled endocytosis or the lysosomal sorting internalized type IIa cotransporter.