Influence of PGP and MRP transporters on etoposide permeability in mouse ileum. Unidirectional (A-B, B-A) and net permeability of etoposide (20 μM) across unstripped ileum from (A) FVB-control and (B) mdr1a (−/−) mice. Values are mean Papp±s.e.mean (cm.s−1) in the absence of inhibitor and following sequential addition of either 200 μM quinidine or a mixture of 200 μM quinidine and 20 μM MK571 in FVB control or following addition of 20 μM MK571 alone in mdr1a (−/−). n=4 – 6 tissues in each direction for both groups, 3 – 6 animals in each group. *P<0.02 compared to A-B in absence of quinidine, **P<0.01 compared to A-B in the presence of quinidine, #P<0.02 compared to A-B in FVB control in absence of quinidine, ##P<0.02 compared to A-B in mdr1a (−/−) in absence of MK571. All comparisons were made using one-way ANOVA.