Naslov
Unchanged expression of the sodium-dependent phosphate cotransporter NaPi-IIa despite diurnal changes in renal phosphate excretion

Autori
Bielesz, B. ; Bacic, D. ; Honegger, K. ; Biber, J. ; Murer, H. ; Wagner, C.A.

Izvornik
Pflügers Archiv European Journal of Physiology (0031-6768) 452 (2006), 6; 683-689

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
sodium-dependent phosphate cotransporter; diurnal changes; renal phosphate excretion

Sažetak
Abstract Renal phosphate excretion is subjected to circadian rhythmicity. The bulk of filtered inorganic phosphate (Pi) is reabsorbed by the sodium-dependent phosphate cotransporter NaPi-IIa. The regulation of proximal tubular phosphate reabsorptive capacity is largely attributed to the altered abundance of NaPi-IIa residing in the brush border membrane (BBM) of proximal tubular cells. Therefore, we examined if the diurnal rise in renal phosphate excretion is accompanied by a corresponding change in NaPi-IIa expression. Renal phosphate excretion, creatinine clearance, and serum phosphate were determined at consecutive time points in rats, starting from 8 a.m. until 5 p.m. During this period, renal phosphate excretion (fractional Pi excretion) increased more than eightfold until 5 p.m. compared to the morning values at 8 a.m. In addition, serum phosphate and creatinine clearance as well as the calculated tubular phosphate threshold increased. Neither immunoblot analysis of BBMs nor immunohistochemical staining for NaPi-IIa yielded evidence for a lower abundance of NaPi-IIa in kidneys collected in the afternoon compared to those in the morning. However, kidneys sampled in the afternoon showed a small decrease (14%) in 32P uptakes into BBM vesicles (BBMVs). Thus, the diurnal rise in renal phosphate excretion was associated with a mild reduction in the sodium-dependent phosphate transport rate in proximal tubular BBMs. There was no apparent downregulation of NaPi-IIa abundance and only a small reduction in Na+-dependent Pi-transport activity. Thus, the diurnal changes in urinary phosphate excretion appear to be mainly related to changes in serum phosphate and tubular threshold but not to NaPi-IIa expression.

Izvorni jezik
Engleski

Znanstvena područja
Socijalne djelatnosti

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