Fig. 2.

Determination of methotrexate (MTX) influx in R1-11 cells transiently transfected with mock, wild-type (WT)-PCFT and mutant constructs in which predicted TMD charged residues were substituted with Leu (D156, E185, E232, E336, R148, R376, K378, and K445) or Ala (R180, K381, and K235). Influx of [³H]MTX (0.5 μM) was assessed at pH 5.5 at 37°C over 1 min. Values are means ± SE from 3 independent experiments. Transport activity in WT-PCFT transfected cells was 75.7 ± 4.6 pmol·mg protein⁻¹·min⁻¹.