Early renal brush border membrane adaptation to dietary phosphorus

The present study evaluated uptake of phosphate by brush border membrane vesicles (BBMV) and alkaline phosphatase activities in brush border membrane fractions in rats fed a normal (0.6%) or low (0.03%) phosphorus diet for 24 h. After 2 min of incubation, the phosphate uptake by BBMV from rats ingesting normal and low phosphorus diets was 1,531 +/- 98 and 2,112 +/- 183 pmol/mg protein, respectively (p less than 0.025); peak glucose uptake was 226 +/- 17 and 209 +/- 42 pmol/mg protein, respectively. Vmax increased 74% in the 0.03% dietary phosphorus groups (p less than 0.005) while Km was similar between groups. Alkaline phosphatase activities were 824 +/- 48 and 816 +/- 56 nmol/min/mg protein with the respective diets. The earliest detectable increase in phosphate uptake by BBMV occurred within 4 h of dietary phosphorus deprivation while alkaline phosphatase increased 3 days later. Renal adaptation to phosphate deprivation can occur within 4 h, is not due solely to a change in the filtered load of phosphate and occurs before increases in the specific activity of alkaline phosphatase.