Distribution of the sodium/phosphate transporter during postnatal ontogeny of the rat kidney.
Renal phosphate reabsorption via the type II sodium/ phosphate cotransporter (NaPi-2) in the brush border membrane (BBM) of proximal tubules underlies alterations during aging. The ontogeny of NaPi-2 in kidneys from newborn to 6-wk-old rats was investigated. NaPi-2 protein distribution in the kidneys of neonatal, 13-d-old, 22-d-old, and 6-wk-old rats was immunohistochemically analyzed, and NaPi-2 mRNA distribution in neonatal and 6-wk-old rats was analyzed by in situ hybridization. In kidneys of newborn rats, the appearance of NaPi-2 protein and mRNA coincided with the development of the brush border (assessed by actin staining) on proximal tubular cells. NaPi-2 was not detectable in the nephrogenic zone or in the outgrowing straight sections of proximal tubules, which lack a brush border. In 13-d-old suckling rats, strong NaPi-2 staining was seen in the BBM of convoluted proximal tubules of all nephron generations. In contrast, in 22-d-old weaned rats, NaPi-2 staining in the BBM of superficial nephrons was weaker than that in the BBM of juxtamedullary nephrons. Western blotting demonstrated that the overall abundance of NaPi-2 protein in the BBM of 22-d-old rats was decreased to approximately 70% of that in 13-d-old rats. In kidneys of 6-wk-old rats, the internephron gradient for NaPi-2 abundance in the BBM corresponded to that in adult rats. The data suggest that the NaPi-2 system in the kidney is fully functional and possesses the capacity for regulation as soon as nephrogenesis is completed. The manifestation of NaPi-2 internephron heterogeneity immediately after weaning might be related to the change in dietary inorganic phosphate content.
Institute of Anatomy, University of Zurich-Irchel, Zurich, Switzerland.
M
M
Traebert
M
M
Lötscher
R
R
Aschwanden
T
T
Ritthaler
J
J
Biber
H
H
Murer
B
B
Kaissling
D000818:Animals; D000831:Animals, Newborn; D000833:Animals, Suckling; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D004032:Diet; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D017136:Ion Transport; D007668:Kidney / Q000254:growth & development* / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000254:growth & development / Q000378:metabolism; D008871:Microvilli / Q000378:metabolism; D009399:Nephrons / Q000254:growth & development / Q000378:metabolism; D010710:Phosphates / Q000008:administration & dosage / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000378:metabolism*; D050608:Sodium-Phosphate Cotransporter Proteins; D050610:Sodium-Phosphate Cotransporter Proteins, Type II; D027981:Symporters
D002352:Carrier Proteins; D010710:Phosphates; D012333:RNA, Messenger; D050608:Sodium-Phosphate Cotransporter Proteins; D050610:Sodium-Phosphate Cotransporter Proteins, Type II; D027981:Symporters; D012964:Sodium