Basolateral Phosphate Transport in Renal Proximal-Tubule-Like OK Cells 1

Abstract

It is generally assumed that phosphate (Pi) effluxes from proximal tubule cells by passive diffusion across the basolateral (BL) membrane. We explored the mechanism of BL PI efflux in proximal tubule-like OK cells grown on permeable filters and then loaded with ³²P. BL efflux of ³²P was significantly stimulated (P < 0.05) by exposing the BL side of the monolayer to 12.5 mM Pi, to 10 mM citrate, or by acid-loading the cells, and was inhibited by exposure to 0.05 mM Pi or 25 mM HCO₃; by contrast, BL exposure to high (8.4) pH, 40 mM K⁺, 140 mM Na gluconate (replacing NaCl), 10 mM lactate, 10 mM succinate, or 10 mM glutamate did not affect BL ³²P efflux. These data are consistent with BL PI efflux from proximal tubule-like cells occurring, in part, via an electro-neutral sodium-sensitive anion transporter capable of exchanging two moles of intracellular acidic H₂PO4^– for each mole of extracellular basic HP04^– or for citrate.