A molecular view of proximal tubular inorganic phosphate (Pi) reabsorption and of its regulation.
In recent years, two mammalian proximal tubular brush border membrane Na/Pi cotransporters (types I and II) have been structurally identified by expression cloning techniques. Oocyte expression studies have shown that only the transport characteristics of the type II transporter correspond to the well-known properties of proximal tubular brush border membrane of Pi transport. In studies on physiological regulation by hormonal and non-hormonal factors a direct involvement and determining role of the type II transporter has been documented. Most interestingly, specific membrane retrieval/insertion phenomena participate in acute (minutes/hours) adjustments of brush border membrane Na/Pi cotransport rates; for chronic (hours/days) alterations also specific resynthesis/degradation processes participate. In pathophysiological alterations (e.g. in X-linked hypophosphataemia and in heavy metal-induced nephrotoxicity) the expression of the type II Na/Pi cotransporters is reduced and explains the observed phosphaturia.
Murer
H
H
Physiologisches Institut, Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland.
Biber
J
J
D000042:Absorption / Q000502:physiology; D000818:Animals; D001692:Biological Transport / Q000502:physiology; D007668:Kidney / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism*; D011817:Rabbits
D010710:Phosphates