The effects of Mendelian mutation on renal sulfate and phosphate transport in man and mouse

We examined renal handling of sulfate and phosphate anions in normal subjects, in patients with two Mendelian disorders of phosphate homeostasis [X-linked hypophosphatemia (XLH) and hypophosphatemic bone disease (HBD)], and in normal male mice (+/Y) and male littermates with murine X-linked hypophosphatemia (Hyp/Y). Serum sulfate was 0.30 +/- 0.04 mmol/l (mean and SD, n = 15) in control human subjects. The corresponding fractional excretion was 0.43 +/- 0.12, and absolute sulfate reabsorption, 15.1 +/- 5.0 mumol/100 ml GF. Patients with impaired phosphate homeostasis had normal renal handling of sulfate. Parathyroid hormone infusion inhibited phosphate reabsorption in normal subjects but did not change tubular reabsorption of sulfate. Serum sulfate was 1.24 +/- 0.20 mmol/l (mean and SD, n = 11) in +/Y mice; the corresponding fractional excretion was 0.38 +/- 0.13. Values in Hyp/Y littermates were not significantly different (1.21 +/- 0.16 mmol/l and 0.32 +/- 0.10, respectively). Brush-border membrane vesicles isolated from Hyp/Y renal cortex demonstrated impaired Na+-dependent phosphate uptake (45% of +/Y control) whereas Na+-dependent sulfate uptake was the same as control. These findings constitute further evidence that sulfate and phosphate anions are conserved from renal filtrate by independent processes in the brush-border membrane of mammalian kidney.