Transport of Phosphate during Development by Renal Brush Border Membrane

Abstract

To elucidate the mechanism for higher tubular reabsorption of Pi (inorganic phosphate) observed in the young growing animals, vesicle preparations of proximal tubule brush border obtained from male Wistar rats of either 4-5 weeks (young) or 9-10 weeks (more mature) of age were used to assess the kinetic characteristics of the Na-Pi cotransporter. No significant difference was noted in the affinity (Km) of this transport system, but the capacity (Vmax) was about 2 times higher in the young than the more mature rat brush border membrane vesicles (BBMV). The results demonstrate that renal adaptation in Pi transport in the proximal tubule brush border membrane during early developmental period is mainly due to higher capacity of the Na-Pi cotransport carrier. However, physical forces along the proximal tubule brush border membrane and extrinsic factors such as growth hormone and parathyroid hormone may have additional role in the maintenance of positive Pi balance during the early developmental period in vivo.