Membrane traffic and control of proximal tubular sodium phosphate (Na/Pi)-cotransport.
Phosphate (P(i)) is freely filtered at the glomerular capillaries and largely reabsorbed in the proximal tubule by a Na-dependent, secondary active transport mechanism. Two different brush border membrane Na/P(i)-cotransporters have recently been "cloned" (type I and type II). Only the type II transporter undergoes physiological regulation (e.g., diet, acid/base, parathyroid hormone); it is also involved in pathophysiological alterations of renal Pi-handling (e.g., X-linked hypophosphatemia). In recent experiments on rats and on tissue culture cells (Opossum kidney cells, OK cells) id was documented that manoeuvres leading to increased uptake involve membrane insertion (fast changes) and new synthesis of type II transporters (slow changes), whereas decreased Na/Pi-cotransport activity is associated with their specific membrane retrieval (fast changes) and lysosomal degradation (slow changes).
Murer
H
H
Institute of Physiology, University of Zurich, Switzerland.
Biber
J
J
D000818:Animals; D002352:Carrier Proteins / Q000502:physiology*; D002478:Cells, Cultured; D004705:Endocytosis / Q000502:physiology; D005247:Feeding Behavior / Q000502:physiology; D005919:Glomerular Filtration Rate / Q000502:physiology; D007687:Kidney Tubules, Proximal / Q000502:physiology*; D008871:Microvilli / Q000502:physiology*; D009893:Opossums; D010281:Parathyroid Hormone / Q000502:physiology*; D010710:Phosphates / Q000378:metabolism; D051381:Rats; D050608:Sodium-Phosphate Cotransporter Proteins; D050609:Sodium-Phosphate Cotransporter Proteins, Type I; D050610:Sodium-Phosphate Cotransporter Proteins, Type II; D027981:Symporters
D002352:Carrier Proteins; D010281:Parathyroid Hormone; D010710:Phosphates; D050608:Sodium-Phosphate Cotransporter Proteins; D050609:Sodium-Phosphate Cotransporter Proteins, Type I; D050610:Sodium-Phosphate Cotransporter Proteins, Type II; D027981:Symporters