Reduced expression of renal Na+ transporters in rats with PTH-induced hypercalcemia.
The purpose of this study was to evaluate whether the natriuresis and polyuria seen in parathyroid hormone (PTH)-induced hypercalcemia are associated with dysregulation of renal Na transporters. Rats were infused with three different doses of human PTH [PTH (1-34); 7.5, 10, and 15 microg.kg(-1).day(-1) s.c.] or vehicle for 48 h using osmotic minipumps. The rats treated with PTH developed significant hypercalcemia (plasma total calcium levels: 2.71 +/- 0.03, 2.77 +/- 0.02, and 3.42 +/- 0.06 mmol/l, respectively, P < 0.05 compared with corresponding controls). The rats with severe hypercalcemia induced by high-dose PTH developed a decreased glomerular filtration rate (GFR), increased urine output, reduced urinary osmolality, increased urinary Na excretion, and fractional excretion of Na. This was associated with downregulation (calculated as a fraction of control levels) of whole kidney expression of type 2 Na-P(i) cotransporter (NaPi-2; 16 +/- 6%), type 3 Na/H exchanger (NHE3; 42 +/- 7%), Na-K-ATPase (55 +/- 2%), and bumetanide-sensitive Na-K-2Cl cotransporter (BSC-1; 25 +/- 4%). In contrast, an upregulation of the Ca(2+)-sensing receptor (CaR) was observed. Rats treated with moderate-dose PTH exhibited unchanged GFR but decreased urinary concentration. The whole kidney expression of NHE3 (52 +/- 8%) and NaPi-2 (26 +/- 5%) was persistently decreased, whereas BSC-1 and Na-K-ATPase protein levels were not altered. CaR expression was also increased. Moreover, rats treated with low-dose PTH showed very mild hypercalcemia but unchanged GFR, normal urinary concentration, and unchanged expression of Na transporters and CaR. In conclusion, the reduced expression of major renal Na transporters is likely to play a role in the increased urinary Na excretion and decreased urinary concentration in rats with PTH-induced hypercalcemia. Moreover, the increase in the CaR in the thick ascending limb (TAL) may indicate a potential role of the CaR in inhibiting Na transport in the TAL.
Wang
Weidong
W
The Water and Salt Research Center, University of Aarhus, DK-8000 Aarhus C, Denmark.
Li
Chunling
C
Kwon
Tae-Hwan
TH
Miller
R Tyler
RT
Knepper
Mark A
MA
Frøkiaer
Jørgen
J
Nielsen
Søren
S
D000818:Animals; D003404:Creatinine / Q000652:urine; D004305:Dose-Response Relationship, Drug; D005919:Glomerular Filtration Rate; D006934:Hypercalcemia / Q000139:chemically induced / Q000175:diagnosis / Q000378:metabolism*; D016623:Ion Pumps / Q000378:metabolism*; D007668:Kidney / Q000378:metabolism*; D008297:Male; D009318:Natriuresis; D010281:Parathyroid Hormone / Q000633:toxicity*; D011141:Polyuria / Q000139:chemically induced; D051381:Rats; D017208:Rats, Wistar; D044169:Receptors, Calcium-Sensing / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism; D050608:Sodium-Phosphate Cotransporter Proteins; D050610:Sodium-Phosphate Cotransporter Proteins, Type II; D028021:Sodium-Potassium-Chloride Symporters / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D064466:Solute Carrier Family 12, Member 1; D027981:Symporters / Q000378:metabolism
D016623:Ion Pumps; D010281:Parathyroid Hormone; D044169:Receptors, Calcium-Sensing; C000613385:SLC9A3 protein, human; C578716:Slc12a1 protein, rat; C000613387:Slc9a3 protein, rat; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D050608:Sodium-Phosphate Cotransporter Proteins; D050610:Sodium-Phosphate Cotransporter Proteins, Type II; D028021:Sodium-Potassium-Chloride Symporters; D064466:Solute Carrier Family 12, Member 1; D027981:Symporters; D012964:Sodium; D003404:Creatinine; D000254:Sodium-Potassium-Exchanging ATPase