Figure 6. Competition between Fe²⁺ and Mn²⁺ for DMT1 transport.

Cells were incubated with ⁵⁴Mn²⁺ and selected concentrations of FeSO₄ with doxycycline (▲ and △) or without (● and ○) for the 2/−IRE (▲ and ●) and the 1A/+IRE (△ and ○) cell lines. Although induced incorporation in the presence of doxycycline was 10- to 15-fold greater than without induction, the incubation without FeSO₄ was treated as 100% uptake for each series to allow comparisons. We fit the concentration response with a single cubic spline because the four series of competitions were indistinguishable. Dropping a line from the 50% level yielded an IC₅₀ at 2.1 μM.