Phosphate uptake by superficial and deep nephron brush border membranes. Effect of the dietary phosphate and parathyroid hormone
Brunette, M.G.; Chan, M.; Maag, U.; Béliveau, R.
Pflugers Archiv European Journal of Physiology 400(4): 356-362
1984
ISSN/ISBN: 0031-6768 PMID: 6462881 Document Number: 225604
Dietary phosphate restriction and acute parathyroidectomy in rat are known to be associated with a selective increase in phosphate uptake by renal cortical brush border membranes (BBM). Conversely, phosphate loading and parathyroid hormone (PTH) administration result in a decrease of this uptake. Whether the response of the membrane to these various stimuli implies similar or different modifications of the kinetic properties of this membrane, whether these modifications affect 1 or both of the 2 systems of phosphate transport, whether both superficial and deep nephron populations are involved and whether the 2 stimuli are additive or not was investigated. Kinetic studies of PO4 uptake by BBM vesicles were performed in 7 groups of rats; control (N), acutely thyroparathyroidectomized (TPTX), PTH loaded (PTH), phosphate loaded (P+), phosphate depleted (P-), phosphate depleted with acute thyroparathyroidectomy (P-TPTX) and phosphate depleted-PTH loaded (P-PTH). In each of these experimental conditions, superficial and deep nephrons were investigated. BBM from deep nephrons present a greater capacity for PO4 transport than those from superficial nephrons; a dual system of PO4 uptake was observed in superficial BBM; deep BBM present only 1 system. Phosphate in the diet influences PO4 uptake by BBM to a greater extent in deep than in the superficial nephrons. PTH status equally influences both populations; TPTX does not significantly enhance PO4 uptake in phosphate depleted rats. PTH loading curtails this uptake. In the deep BBM neither the PTH status nor the phosphate content of the diet modify the apparent Km. In the the superficial BBM, the apparent Km of the high affinity system (low substrate concentrations) varies with the PTH activity.