FIGURE 3.

Influence of preincubation of COS7 cells with unlabeled polyamines in polyamine uptake. A, cells at 80% of confluency were incubated for 90 min with 100 μm of putrescine (Put), spermidine (Spd), or spermine (Spm). After washing twice with DMEM, polyamine uptake was carried out using 2 μm ¹⁴C-labeled putrescine for 30 min. B, cells were pretreated with 100 μm of unlabeled putrescine plus 100 μm of cycloheximide (Chx), and putrescine uptake was compared with their controls in the absence of cycloheximide. Data are shown as mean ± S.E. of triplicate determinations.