Fig. 1. Cellular uptake of ¹²⁵I-Tf in confluent MCF-7, 5637 and Caco-2 cell monolayers.

Confluent MCF-7 (open circles), 5637 (open squares) and Caco-2 (solid circles) cells grown for 6 days on 12-well cluster plates were pre-incubated with serum free medium at 37°C for 1 h to deplete serum Tf. Subsequently, ¹²⁵I-Tf (3 μg/ml) was added to cells and incubated for different time intervals at 37°C. Cells were then washed with cold PBS and solubilized by incubation with 1 N NaOH. The cell lysate was assayed by using a Packard gamma counter. Non-specific binding was determined in parallel wells. Each point represents the mean of three measurements with error bars representing the standard deviation.