Transepithelial phosphate transport in rabbit proximal tubular cells adapted to phosphate deprivation

Both renal and nonrenal cells in culture adapt to deprivation of Pi by increasing Na-dependent Pi uptake. We studied whether this change in uptake is reflected in an increased renal transepithelial Pi transport. We grew primary cultures of rabbit renal cortical cells in plastic flasks and subcultured them onto Millicell-HA filters. This produced cell monolayers, which structurally and functionally resembled proximal tubule. These cells performed Na-dependent net transepithelial transport of 32Pi in the apical-to-basolateral direction that was inhibited by phosphonoformic acid in the apical fluid or by ouabain in the basolateral fluid or by preincubation with parathyroid hormone. Overnight incubation at low Pi concentrations led to a progressive increase in 5-min Na-dependent Pi uptake into cell monolayers. Na-dependent Pi uptake was threefold higher following overnight incubation at 25 microM Pi, compared with 3 mM Pi, and the increase was one-half maximal with incubation at an extracellular Pi concentration ([Pi]) of 300 microM. This was associated with a decrease in Na-dependent transepithelial Pi flux to the basolateral fluid by the same cells, which fell dramatically following incubation at < or = 300 microM Pi. There was no change in Na-dependent uptake or transepithelial transport of L-glutamine. This adaptation to Pi deprivation in vitro appears to serve to restore depleted cell stores of Pi rather than to regulate transepithelial Pi transport.