Sodium-dependent phosphate co-transporters

The renal proximal tubular reabsorption of inorganic phosphate (Pi) mediate d by sodium-dependent phosphate (Na+/Pi) co-transporters plays a critical r ole in the maintenance of Pi homeostasis. Two nonhomologous Na+/Pi co-trans porters (type I and type II) have been identified in the renal cortex of va rious species. The role of the type I co-transporter in Pi regulation remai ns to be clarified. Type II co-transporters play a major role in the regula tion of renal Pi reabsorption by dietary Pi and parathyroid hormone, which regulate the rapid endocytosis/ exocytosis of the transporters. Type III Na +/Pi co-transporters, which are expressed in a wide variety of tissues and are regulated by changes in the Pi concentration, have recently been descri bed. The presence of a novel Pi regulating hormone called 'phosphatonin' ha s been postulated in studies of the mechanisms of X-linked hypophosphatemic rickets and oncogenic osteomalacia. The regulation of phosphatonin and Na/Pi cotransporters may provide novel pharmacological approaches to the trea tment of these diseases. (C) 1999 Elsevier Science Ltd. All rights reserved .