Developmental differences in renal sulfate reabsorption: transport kinetics in brush border membrane vesicles

Abstract

Renal tubular reabsorption of inorganic sulfate is greater in younger than older guinea pigs. To determine the mechanism of this difference, we studied the transport of inorganic sulfate in renal brush border membrane vesicles (BBMV) obtained from young (< 25 days) and adult guinea pigs (> 60 days). BBMV were obtained by mechanical and osmotic disruption of dissected renal cortices followed by magnesium precipitation and differential centrifugation. After the membranes were incubated for 10 s in solutions containing inorganic sulfate at several concentrations (0.1-10 mM) and trace amounts of 35sulfate, intravesicular uptake was measured. Based on 35sulfur uptake, reabsorption transport kinetics (Vmax and Km) were estimated. BBMV obtained from young guinea pigs demonstrated higher sodium-sulfate cotransport, Vmax (51.79 +/- 4.34 pmol/mg protein per s) than those obtained from adult animals (Vmax = 34.28 +/- 9.17 pmol/mg per s), P < 0.05. Vmax values are represented as means plus or minus standard deviation. No differences in Km were observed. Our results indicate that age-related differences in renal inorganic sulfate reabsorption are due to a higher Vmax for sodium-sulfate cotransport in the younger animals, suggesting a higher density of sodium-sulfate cotransporters or an increased cotransport turnover rate in this age group.

Renal brush border sodium-sulfate cotransport in guinea pig: effect of age and diet

“…This may explain the increased sulfate reabsorption previously noted in young guinea pigs [2,3] and suggests a requirement to maintain a positive sulfate balance and a net conservation of inorganic sulfate during growth. While a sulfur-free diet produced no additional increase in Vmax, a high-sulfate intake produced a decrease in sodium-sulfate cotransport Vmax.…”

“…In a previous study, a linear increase in BBMV uptake was observed during the first 15 s of vesicular sulfate uptake. Measuring uptake at 10 s was well within the linear portion of the curve [3].…”

“…Uptake of phosphate and D-glucose was measured as described for sulfate except that 10 ml of vesicle preparation was incubated with 40 ml of transport medium [3,9]. Incubations for sulfate, phosphate, and glucose were carried out in five replicates with freshly prepared membranes.…”

“…The pK1 is less than 2 and the pK2 is greater than 9. Age has also been shown to have a significant effect on renal sulfate reabsorption [2,3]. For changes in sulfate reabsorption related to age and diet, renal tubular adaptation is suggested; but an exact mechanism has not been established.…”

Abnormal sulfate metabolism in vitamin D-deficient rats.

“…Inorganic sulfate is essential for a variety of metabolic processes, and sulfate requirements in man and other mammalian species appear to change as a function of growth and age (34)(35)(36). Thus, mechanisms permitting the regulation of plasma sulfate levels are likely to be important for normal physiology, and abnormalities in these processes may contribute to the pathogenesis of various diseases.…”