Chloride dependency of renal brush-border membrane phosphate transport

In our present study, we examined the effect of Cl- on rabbit renal brush-b order membrane (BBM) phosphate (P-i) uptake. It was found that the Na+-depe ndent BBM P-32 uptake was significantly inhibited by Cl- replacement in the uptake solution with other anions, or by Cl- transport inhibitors, includi ng DIDS, SITS, diphenylamine-2-carboxylate (DPC), niflumic acid (NF), and 5 -nitro-2-(3-phenylpropylamino)benzoate (NPPB). Intravesicular formate or Cl - increased BBM Cl-36-uptake but did not affect BBM P-32 uptake. BBM Na-22( +) uptake was lowered by Cl- replacement in the uptake solution but not by Cl- transport inhibitors. Changes in transmembrane electrical potential alt ered BBM Cl-36(-) and P-32 uptake in directions consistent with a net inwar d movement of negative and positive charges, respectively. However, the Cl- -dependent BBM P-i uptake was not affected by changes in transmembrane elec trical potential. Finally, a similar Cl- dependency of P-i uptake was also found with BBM derived from rat and mouse kidneys. In summary, our study sh owed that a component of Na+-dependent P-i uptake was also Cl- dependent in rabbit, rat, and mouse renal BBM. The mechanism underlying this Cl- depend ency remains to be identified.