Fig. 6.

Pattern of P_i transport inhibition. A: normalized graphs of P_i uptake inhibition with several substrates. ³²P_i uptake was assayed at 50 μM for 20 min. Solid and shaded bars indicate significant (complete or partial, respectively) inhibition compared with the control (Con; open bars). P_i, phosphonoformic acid (PFA), and arsenate (As^V) were used at 5 mM; alanine (Ala), glutamate (Glu), formate (Form), sulfate (SO₄), oxalate (Ox), and carbonate (HCO₃) were used at 10 mM; DIDS and SITS were used at 0.1 mM. The dashed line indicates the level of inhibition with 5 mM P_i as an inhibitor. A: effect on 1 mM P_i-maintained Caco2BBE cells (1), effect on 4 mM P_i-preincubated Caco2BBE cells (2), and absence of metabolic/toxic effects of the inhibitors after 20 min of preincubation in the absence of ³²P_i (3). B: dose-response relationships of the indicated inhibitors using Caco2BBE cells incubated with 1 or 4 mM P_i. The corresponding mean inhibitory concentrations are indicated.