title: Effect of pH on Na(+)-dependent phosphate transport in renal outer cortical and outer medullary BBMV.
abstract: The influence of pH on sodium-phosphate cotransport was determined in brush-border membrane vesicles (BBMV) isolated from outer cortical and outer medullary tissue of porcine kidneys. Two transport systems are apparent in outer cortical brush-border vesicles, and one process is apparent in outer medullary vesicles at all pH values. The apparent maximum uptake rate (Vmax) of the low-affinity system in outer cortex vesicles decreased from 8.3 +/- 1.7 to 3.2 +/- 0.05 nmol.mg protein-1.min-1 with pH change of 8.0 to 6.0, and the high-affinity process changed from 1.3 +/- 0.2 to 0.1 +/- 0.01 nmol.mg protein-1.min-1. The respective affinity values (Km) also decreased 5.5 +/- 0.9 to 0.6 +/- 0.01 mM and 0.08 +/- 0.005 to 0.01 +/- 0.005 mM, respectively, with acidification. In outer medullary vesicles a decrease in pH diminished the apparent Km, 0.28 +/- 0.03 to 0.02 +/- 0.003 mM, and mean Vmax from 3.0 +/- 0.07 to 0.5 +/- 0.1 nmol.mg protein-1.min-1. The mean KNaD values were 22.1 +/- 4.2 mM in outer cortical vesicles (low-affinity system) and 58.7 +/- 7.2 mM in outer medullary vesicles (high-affinity system) and were not altered by pH, suggesting that H+ does not affect the sodium interactive site. The data suggest that the vesicles prepared from outer cortical and outer medullary tissue possess distinctive sodium-phosphate transporters that are sensitive to external H+ concentrations.
authors.affiliation: Department of Medicine, University Hospital, University of British Columbia, Vancouver, Canada.
authors.forename: G A
authors.initials: GA
authors.lastname: Quamme
mesh_terms: D000818:Animals; D001692:Biological Transport; D006863:Hydrogen-Ion Concentration; D007672:Kidney Cortex / Q000378:metabolism* / Q000648:ultrastructure; D007679:Kidney Medulla / Q000378:metabolism* / Q000648:ultrastructure; D007700:Kinetics; D008871:Microvilli / Q000378:metabolism; D010710:Phosphates / Q000378:metabolism*; D011522:Protons; D012964:Sodium / Q000494:pharmacology*; D013552:Swine
chemical_list: D010710:Phosphates; D011522:Protons; D012964:Sodium