Characterization of sodium‐independent Pi uptake in Caco2 cells (908.3)

Abstract

While inorganic phosphate (Pi) uptake in epithelia has both Na‐dependent and Na‐independent components, only Na‐dependent transporters have been identified to date. In this work we have characterized the Na‐independent Pi uptake in the intestinal Caco2BBe cell line, as a preliminary step in the molecular identification of novel intestinal Pi transporters.Caco2BBe cells grown in DMEM were incubated overnight in the presence of 1 or 4mM Pi to mimic the intestinal adaptation to high Pi diet recently described. Only Na‐independent Pi uptake was observed in these cells, which was dramatically increased in cells preincubated with 4mM Pi. Uptake in 1mM Pi adapted cells decreased with alkaline pH, but it increased with the pH at 4mM Pi. The increase in Pi transport at 4mM Pi was completely inhibited by Pi, phosphonoformic acid and oxalate, while DIDS, SITS, SO4=, and CO3= did not. Km values were 0.06 and 0.2 mM after adaptation to 1 and 4 mM Pi, respectively.In conclusion, two different Na‐independent Pi transports are expressed in Caco2BBe cells, one of them being overexpressed when preincubated with high Pi medium. The molecular identity of the transporters are still unkown.