Inhibition Assay: MDCK cells stably transfected with rat PGT (Endo et al., 2002) were seeded at 15-20% confluence on 24-well plates. The day on which the cells were seeded was considered day 1. PGE2 uptake experiments were conducted on day 4. All of the PGE2 uptake experiments were conducted at room temperature. On day 4, cells were washed twice with Waymouth buffer (135 mM NaCl, 13 mM H-Hepes, 13 mM Na-Hepes, 2.5 mM CaCl2, 1.2 mM MgCl2, 0.8 mM MgSO4, 5 mM KCl, and 28 mM D-glucose). Then 200 μL of Waymouth buffer containing [3H]PGE2 (purchased from Perkin Elmer) was added to each well. At the designed time, the uptake of [3H]PGE2 was stopped by aspiration of uptake buffer; this was followed by immediate washing twice with 500 μL of chilled Waymouth buffer. Cells were then lysed with 100 μL lysis buffer containing 0.25% SDS and 0.05 N NaOH. 1.5 mL of scintillation solution was added to each well, and intracellular [3H]PGE2 was counted by MicroBeta Counter.