The main non-hormonal mechanism for controlling Pi homeostasis is renal adaptation of the proximal tubular Pi transport rate to changes in dietary phosphate content. OK cell line is an in vitro renal model that maintains the ability of renal adaptation to the extracellular Pi concentration. We have studied how two competitive inhibitors of Pi transport, arsenate (As^V) and phosphonoformate (PFA), affect adaptation to low and high Pi concentrations. OK cells show very high affinity for As^V (K_i 0.12 mM) compared to the kidney. AsV very efficiently reversed the adaptation of OK cells to low Pi (0.1 mM), while PFA induced adaptation similar to 0.1 mM Pi. Adaptation with 2 mM Pi or As^V was characterized by decreases in the V_max of Pi transport and an abundance of the NaPi-IIa Pi transporter in the plasma membrane, shown by the protein biotinylation. Conversely, PFA and 0.1 mM Pi increased the Vmax and transporter abundance. Changes in the V_max were limited to a 50% variation, which was not paralleled by changes in the concentration of Pi or of the inhibitor. OK cells are very sensitive to As^V, but the effects are reversible and non-cytotoxic. These effects can be interpreted as arsenate being transported into the cell, thereby mimicking a high Pi concentration. PFA blocks the uptake of Pi but is not transported, and it therefore simulates a low Pi concentration inside the cell. To conclude, a mathematical definition of the adaptation process is reported, thereby explaining the limited changes in Pi transport V_max.