Basolateral Phosphate Transport in Renal Proximal-Tubule-Like OK Cells¹

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.

Unique uptake and efflux systems of inorganic phosphate in osteoclast-like cells

“…Furthermore, analysis of [ 14 C]PFA uptake indicates that PFA does not exchange with intracellular P i , suggesting that PFA stimulates P i efflux by a mechanism different from the P i /PFA exchange system. In contrast, BaracNieto et al (1) demonstrated the presence of a P i -anion ex- change mechanism across the basolateral membrane of proximal tubule-like cells. The basolateral membrane of renal proximal tubule has a transporter that is capable of exchanging 2 moles of intracellular H 2 PO 4…”

“…Cell densities were ϳ1.6 ϫ 10 4 cells per well. Pi efflux was measured with a modification of a previously described procedure (1,16,32). The cell monolayers were gently washed three times with 0.5 ml of prewarmed (37°C) uptake solution (mM: 137 NaCl, 5.4 KCl, 2.8 CaCl 2, 1.2 MgCl2, and 10 HEPES-Tris, pH 7.4) for Na ϩ -dependent Pi uptake assays, and NaCl was replaced with choline chloride for Na ϩ -independent Pi uptake assays.…”

Expression of the mammalian Xenotropic Polytropic Virus Receptor 1 (XPR1) in tobacco leaves leads to phosphate export

“…Analysis of XPR1 mRNA expression profile using array databases (www.genevestigator.com) reveals a very broad expression pattern in tissues as diverse as brain, kidney, skin, liver, heart and lung. Interestingly, Pi efflux has also been reported in a broad range of cells, such as pancreatic B cells [25], non-myelinated nerve fibers [26], osteoclasts [27], hepatocytes [28], myocardiocytes [29], jejunal enterocytes [30] and cells of the renal proximal tubules [31]. Altogether, these data indicate that control of Pi efflux has an important physiological role in various tissues.…”

The Phosphate Exporter xpr1b Is Required for Differentiation of Tissue-Resident Macrophages

“…small intestine enterocytes and proximal tubule cells) and cells involved in bone resorption (osteoclasts). In fact, the presence of a dedicated phosphate exporter has long been hypothesized in epithelial renal cells and osteoclasts (Barac-Nieto et al, 2002, Ito et al, 2007). In particular, osteoclasts were shown to have a unique Pi efflux system, involved in the continuous release of Pi at the basolateral plasma membrane preventing accumulation of intracellular inorganic phosphate (Ito et al, 2007).…”