Renal Na(+)-phosphate cotransport in X-linked Hyp mice responds appropriately to Na+ gradient, membrane potential, and pH.
To investigate the mechanism for the 50% decrease in Vmax of the high-affinity phosphate transport system in the renal brush-border membrane of X-linked Hyp mice, we compared the effects of external Na+ concentration, membrane potential, pH, phosphonoformic acid (PFA), and arsenate on Na(+)-Pi cotransport in brush-border membrane vesicles prepared from normal mice and Hyp littermates. The affinity of the Na(+)-Pi cotransport system for Na+ (apparent Km = 60 +/- 7 and 64 +/- 2 mM for normal and Hyp mice, respectively) and the Na(+)-Pi stoichiometry estimated from Hill plots (2.5 +/- 0.2 and 2.9 +/- 0.6 for normal and Hyp mice, respectively) were similar in brush-border membranes of both strains. Inside-negative membrane potential, generated by anions of different permeabilities, stimulated Na(+)-Pi cotransport and inside-positive membrane potential generated by valinomycin, and a K+ gradient (outside greater than inside) inhibited Na(+)-Pi cotransport to the same extent in brush-border membranes derived from normal mice and Hyp littermates. The pH dependence of Na(+)-Pi cotransport was similar in brush-border membrane vesicles of normal and Hyp mice. The ratio of Na(+)-Pi cotransport measured at pH 7.5 relative to that at pH 6.5 was 2.9 +/- 0.6 in normal mice and 2.9 +/- 0.7 in Hyp mice. PFA was a competitive inhibitor of Na(+)-Pi cotransport in brush-border membranes of both normal and Hyp mice. However, the apparent Ki for PFA was significantly lower in Hyp mice (0.31 +/- 0.01 and 0.19 +/- 0.02 mM in normal and Hyp mice, respectively, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
Harvey
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Department of Pediatrics, McGill University, Montreal, Quebec, Canada.
Tenenhouse
H S
HS
D000818:Animals; D001149:Arsenates / Q000494:pharmacology; D001692:Biological Transport / Q000502:physiology; D017245:Foscarnet; D008040:Genetic Linkage / Q000235:genetics*; D006863:Hydrogen-Ion Concentration; D007015:Hypophosphatemia, Familial / Q000235:genetics* / Q000378:metabolism; D007668:Kidney / Q000378:metabolism* / Q000648:ultrastructure; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008817:Mice, Mutant Strains; D008871:Microvilli / Q000187:drug effects; D010710:Phosphates / Q000097:blood / Q000493:pharmacokinetics*; D010746:Phosphonoacetic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D012964:Sodium / Q000493:pharmacokinetics*; D014960:X Chromosome
D001149:Arsenates; D010710:Phosphates; D017245:Foscarnet; D012964:Sodium; C025657:arsenic acid; D010746:Phosphonoacetic Acid