Figure 3. Inhibition of rhodamine 123 efflux by methadone.

(a) Methadone inhibited P-gp mediated efflux of rhodamine 123 in a concentration dependent manner. Verapamil 10 µM was used as a positive control for the inhibition model. Methadone significantly inhibited rhodamine 123 efflux in wild-type P-gp, as well as the two variant-types of P-gp. *p<0.05 compared withrhodamine123transport without methadone. (b) Dose-response study of rhodamine 123 efflux in the presence of methadone (0.5–100 µM). Data were presented as mean ± SE of at least three experiments, each in triplicate.