Effect of parathyroid hormone and dietary phosphate on phosphate transport in renal outer cortical and outer medullary brush-border membrane vesicles.
Two distinctive sodium-dependent phosphate transport systems have been identified in early and late proximal tubules; a high-capacity process located only in outer cortical tissue, and a high affinity present in both outer cortical and outer medullary brush-border membranes (Km 0.1-0.25 mM). A third, sodium-independent, pH gradient-stimulated system (Vmax 4.7 +/- 0.3 nmol.mg-1.min-1, Km 0.15 +/- 0.002 mM) is present in the outer medulla, but absent in outer cortex. Brush-border vesicles were prepared from outer cortical and outer medullary tissue of pigs maintained on low (less than 0.05%), normal (0.4%), or high (4%) phosphate diets. Sodium-dependent phosphate uptake of the high-capacity system decreased (Vmax, 9.4 to 2.2 nmol.mg-1.min-1) from low to high phosphate diet, whereas uptake rates decreased about 50% in the high-affinity system. There were no changes in the respective Km values. The pH gradient-stimulated uptake also decreased (Vmax, 6.9 to 3.0 nmol.mg-1.min-1) with no change in mean Km value (0.15 +/- 0.001 mM) with dietary manipulation. Administration of 1 U parathyroid hormone prior to study resulted in a decrease in sodium-dependent uptake by 40-50% and in pH-dependent uptake (36%) with no change in the respective Km values. In conclusion, the antecedent dietary phosphate intake and parathyroid hormone administration appropriately alters phosphate uptake across the brush-border membrane of all three systems, sodium-dependent and pH gradient-stimulated phosphate transport.
Quamme
G A
GA
Department of Medicine, University Hospital University of British Columbia, Vancouver, Canada.
D000818:Animals; D001692:Biological Transport; D004032:Diet; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007672:Kidney Cortex / Q000378:metabolism*; D007679:Kidney Medulla / Q000378:metabolism*; D007700:Kinetics; D008871:Microvilli / Q000378:metabolism; D010281:Parathyroid Hormone / Q000494:pharmacology*; D010710:Phosphates / Q000378:metabolism*; D012964:Sodium / Q000502:physiology; D013552:Swine
D010281:Parathyroid Hormone; D010710:Phosphates; D012964:Sodium