Fig. 4.

Kinetics of ferroportin-mediated metal efflux. Oocytes were injected with 50 nl of 50 μM ⁵⁷Co. A: total ⁵⁷Co efflux (in pmoles per oocyte) as a function of time in control oocytes (gray) and oocytes expressing Fpn-EGFP (black). Data from oocytes expressing Fpn-EGFP were fit by linear regression (y-intercept constrained at 0) over the following ranges of time points: 0–240 min (short dashed black line), root-mean-square error (RMSE) = 0.32, adjusted r² = 0.86, P < 0.001; 0–120 min (long dashed black line), RMSE = 0.12, adjusted r² = 0.97, P < 0.001; 0–60 min (solid black line), RMSE = 0.055, adjusted r² = 0.99, P < 0.001; and 0–30 min (line not shown for clarity), RMSE = 0.063, adjusted r² = 0.93, P < 0.001. B: first-order rate constants (k) for ⁵⁷Co efflux as a function of time in control oocytes (gray) and oocytes expressing Fpn-EGFP (black) (n = 8–12 per group), from the same experiment as that depicted in A. Two-way ANOVA revealed an interaction (P < 0.001); Fpn differed from control at all time points (P < 0.001). Within Fpn, 120- and 240-min time points differed from 60 min (P ≤ 0.008). C: first-order rate constants (k) for ⁵⁷Co efflux (over 30 min) in intact (solid bars) or semipermeabilized (hatched bars) control oocytes and oocytes expressing Fpn-EGFP (n = 20–30 per group). Oocytes were pretreated for 30 min in MBM containing 1% dimethyl sulfoxide and 0.1% bovine serum albumin, without or with 100 μg/ml amphotericin B as permeabilizing agent. Two-way ANOVA revealed an interaction (P < 0.001); intact Fpn differed from intact control (P = 0.008); within Fpn, intact differed from semipermeabilized (P < 0.001). (Data in C are from an oocyte preparation independent of that used in A and B).