X-linked hypophosphatemic Gy mice: renal tubular maximum for phosphate vs. brush-border transport after low-P diet.
We examined the effect of the X-linked hypophosphatemic Gy mutation on the maximal renal tubular reabsorption of phosphate (TmP) and compared the effects of phosphate deprivation on both TmP and Na(+)-dependent phosphate transport in renal brush-border membrane vesicles (BBMV). Adult female normal and Gy mice were fed a control (1.0% P) or low-phosphate (0.03% P) diet for 5 days. For TmP measurement, anesthetized mice were infused intravenously with [3H]inulin and increasing increments of phosphate (0, 0.27, 0.54, and 1.08 mumol/min). TmP was significantly reduced in Gy mice on the control diet. Normal mice responded to the low-phosphate diet by raising their TmP [2.35 +/- 0.12 (n = 9) vs. 3.71 +/- 0.16 (n = 9) mumol/ml glomerular filtrate, mean +/- SE, P < 0.001], whereas in Gy mice, the change was not significant [1.46 +/- 0.10 (n = 10) vs. 1.70 +/- 0.11 (n = 10)]. In contrast, Gy mice did respond to phosphate restriction by increasing the initial-rate Na(+)-dependent phosphate transport in the renal BBMV [314 +/- 11 (n = 5) vs. 1,105 +/- 157 (n = 5) pmol.mg protein-1.6 s-1, P < 0.01] as did normal mice [583 +/- 64 (n = 5) vs. 1,692 +/- 203 (n = 5) pmol.mg protein-1.6 s-1, P < 0.01]. In conclusion, the adaptive increase in Na(+)-phosphate cotransport in the brush-border membrane of the proximal tubule is not sufficient for the overall increase in TmP in the whole kidney in response to dietary phosphate deprivation.
Thornton
S W
SW
Department of Biology, University of North Carolina at Charlotte 28223.
Tenenhouse
H S
HS
Martel
J
J
Bockian
R W
RW
Meyer
M H
MH
Meyer
R A
RA
D000042:Absorption; D000818:Animals; D001692:Biological Transport; D003433:Crosses, Genetic; D004032:Diet; D005260:Female; D005838:Genotype; D005919:Glomerular Filtration Rate; D006579:Heterozygote; D017674:Hypophosphatemia / Q000235:genetics* / Q000378:metabolism*; D007684:Kidney Tubules / Q000378:metabolism* / Q000502:physiology / Q000503:physiopathology; D008297:Male; D051379:Mice; D008809:Mice, Inbred C3H; D008817:Mice, Mutant Strains; D008871:Microvilli / Q000378:metabolism*; D010710:Phosphates / Q000097:blood / Q000172:deficiency* / Q000378:metabolism*; D012016:Reference Values; D014960:X Chromosome
D010710:Phosphates