Adaptation of Opossum Kidney Cells to Luminal Phosphate: Effects of Phosphonoformic Acid and Kinase Inhibitors

Abstract

Background/Aims: Renal reabsorption of inorganic phosphate (Pi) is mediated by SLC34 and SLC20 Na+/Pi-cotransporters the abundance of which is under hormonal control. Extracellular Pi itself also regulates the expression of cotransporters and the concentration of Pi-regulating hormones, though the signaling pathways are largely unknown. Here, we explored the mechanisms that allow renal proximal cells to adapt to changes in the concentration of Pi. Methods: opossum kidney (OK) cells, a model of proximal epithelia, were incubated with different concentrations of Pi in the absence/presence of phosphonoformic acid (PFA), a Pi-analogue and SLC34-inhibitor, and of inhibitors of kinases involved in hormonal control of Pi-homeostasis; cells cultured in normal media were treated with uncouplers of oxidative phosphorylation. Then, the intracellular concentration of ATP and/or the Pi-transport capacity of the cultures were analyzed. Results: luminal Pi regulates the Pi-transport and the intracellular ATP levels. Changes in ATP seem secondary to alterations in Pi-transport, rather than ATP acting as a signal. Adaptation of Pi-transport to high Pi was not mimicked by PFA. Transport adaptation was blocked by PFA but not by kinase inhibitors. Conclusions: in OK cells, adaptation of Pi-transport to luminal Pi does not depend on the same signaling pathways involved in hormonal regulation.

Keywords

• Proximal tubule
• Reabsorption of phosphate
• Phosphate sensing
• OK cells