Molecular regulation of renal phosphate transport

This review has focused on the regulation of renal inorganic phosphate (Pi) transport in response to changes in dietary Pi and parathyroid hormone (PTH). Both dietary Pi and PTH produce rapid and marked changes in proximal tubular Pi transport which is paralleled by marked alterations in the abundance of NaPi-2 protein in the apical brush border membrane (BBM) of the proximal tubule. It appears that rapid insertion and retrieval of Na/Pi cotransporters into and out of the BBM plays a major role in the acute regulation of renal Pi transport. The acute regulation of the renal Na/Pi cotransporter thus far seems remarkably similar to the regulation of the glucose transporter (GLUT 4) by insulin (Verhey, Yeh and Birnbau, 1995; Yang et al., 1996; Zorzano et al., 1996) and the water channels (Aquaporin 1 and Aquaporin 2) by vasopressin (Elkjaer et al., 1995; Nielsen et al., 1995; Katsura et al., 1995). In the case of the Na/Pi cotransporter, future work will be directed in defining the cellular trafficking mechanisms, the regulation of endocytosis and exocytosis by physiological stimuli, and their relationship to intracellular signaling pathways.