Towards a Molecular View of Renal Proximal Tubular Reabsorption of Phosphate

Abstract

Apical sodium-dependent transport of inorganic phosphate (Pi) in the proximal tubule plays a crucial role in renal Pi reabsorption and consequently in the maintenance of Pi homeostasis. This transport system represents a main target for acute and long-term regulation such as by parathyroid hormone, by growth factors and dietary intake of phosphate. In this short review we briefly describe the currently established cellular mechanism of proximal tubular Pi reabsorption and its regulation via the apical Na/Pi cotransport system. In a second part we will outline recent progress made with respect to the molecular cloning of renal Na/Pi cotransport systems. Knowledge about the molecular identity of these transport systems will make it possible to resolve yet unanswered questions about the molecular mechanisms involved in the physiology of the regulation of renal Pi reabsorption.

Diuretics

“…This has been observed, for instance, for the expression of a sodium-phosphate transport system in the brush-border membrane of the proximal tubule (BIBER et aL 1993;LEVI et aI., 1994). This has been observed, for instance, for the expression of a sodium-phosphate transport system in the brush-border membrane of the proximal tubule (BIBER et aL 1993;LEVI et aI., 1994).…”

“…Carbonic anhydrase is abundant not only in the cytoplasm, but also in both membrane domains of the proximal tubule cells (DOBYAN et al 1982;BROWN et al 1983;SEKI and FROMTER 1992). The brush border membrane houses a great variety of specific transport proteins (e.g., SANDS et al 1992;BURCKHARDT and KINNE 1992;BIBER et al 1993; for further refs. see MAUNSBACH and CHRISTENSEN 1992).…”

“…Figure 10 lists the major transport systems in the proximal tubule: Na + entry across the luminal cell membrane proceeds through Na + IH+ exchange (BORON 1992;BORON and BOULPAEP 1989;MURER et al 1976) and Na + -coupled transport for D-glucose HEDIGER et al 1987;KINNE 1976;KOEPSELL et al 1990;SACKTOR 1989;SAMARZIJA et al 1982;SCHAFER and WILLIAMS 1985), amino acids (HOSHI 1990;HOSHI et al 1976;SAMARZIJA and FROMTER 1982a,b,c;SAMARZIJA et al 1982;SILBERNAGL 1988;ZELIKOVIC and CHESNEY 1989), organic acids (MURER and BURCKHARDT 1983;ULLRICH et al 1982a,b,c), sulfate (MURER and BURCKHARDT 1983;TURNER 1984;ULLRICH et al 1982a) and phosphate (BIBER 1989;BIBER and MURER 1993). Furthermore, the proximal tubule secretes several organic acids and bases as well as NHt.…”