Effect of NPPB and phloretin (Phlor.) on the increase of transepithelial and transmembrane urea flux due to VacA. (a) Polarized MDCK II monolayers were treated with 125 nM activated VacA for 3 hours and then washed and further assayed for [¹⁴C]urea transepithelial flow in the presence of the indicated concentrations of NPPB or phloretin (added to both apical and basolateral compartments). (b) Nonpolarized AGS cells were intoxicated by 125 nM of VacA at 37°C for 3 hours, and assayed for initial rate of [¹⁴C]urea cell influx and efflux, in the presence of 250 μM phloretin or NPPB. Data are expressed as percent of the increase observed in controls (+VacA, no inhibitor). Data are the mean of three experiments run in duplicate ± SE.