Decreased luminal membrane transport of phosphate in chronic renal failure

To examine the effects of the hyperparathyroidism that accompanies chronic renal failure (CRF) on Pi transport across the renal proximal tubular luminal membrane, brush border membrane vesicles (BBMV) were prepared from the viable portion of the kidney of dogs with CRF or normal renal function. Initial rates of Na+ gradient-dependent Pi transport were decreased in BBMV from dogs with CRF compared with normal dogs. Initial rates of 22Na+ uptake in BBMV from dogs with CRF, however, were increased, suggesting a more rapid dissipation of the Na+ gradient in these vesicles. Initial rates of Pi transport measured under Na+-equilibrated conditions were decreased in BBMV from dogs with CRF. Parathyroidectomy of dogs with CRF abolished this decrease in Pi uptake. We conclude that the adaptations in Pi excretion associated with CRF are accompanied by changes in Na+-dependent Pi transport in BBMV and, therefore, possibly across the luminal membrane of the renal tubule. Moreover, the activity of this transport system can be altered by parathyroidectomy of dogs prior to isolation of BBMV.