Fig. 2

BAP is a specific, competitive inhibitor of the nonselective polyamine transporter in human monocyte cultures, (a) BAP inhibits spermine uptake in LPS-stimulated human monocytes. Human monocytes were stimulated by LPS (100 ng/ml) for 2 hr, then treated with BAP in the concentrations indicated for 30–60 min followed by 25 min incubation with 35 µM spermine with ¹⁴C-labeled spermine tracer at either 4°C or 37°C. Spermine uptake (CPM) is defined by the difference between cell-associated radioactivity at 37°C and that at 4°C, and expressed as percentage of the control (no BAP) cultures. Results are percentage of control mean ± SE. (b) Competitive inhibition of spermine uptake by BAP. Human monocytes were stimulated by LPS (100 ng/ml) for 2 hr, then incubated with the indicated concentrations of spermine with ¹⁴C-labeled spermine tracer at either 4°C or 37°C for 25 min in the absence or presence of 500 µM of BAP. Cell-associated radioactivity (CPM) was then measured, and spermine uptake (CPM) in human monocytes is shown as a reciprocal plot. The heavy line denotes spermine uptake in the absence of BAP, and the thin line, in the presence of BAP. (c) BAP inhibition of polyamine uptake is specific. Human monocytes were stimulated by LPS (100 ng/ml) for 2 hr, then incubated individually with ¹⁴C-labeled spermine, putrescine, glutamine, or aspartic acid at 37°C for 25 min in the absence or presence of BAP at the concentrations indicated. Cell-associated radioactivity (CPM) was measured and presented as percentage of control (no BAP) ± SE.