MECHANISM OF SPERMIDINE UPTAKE IN CULTURED-MAMMALIAN-CELLS AND ITS INHIBITION BY SOME POLYAMINE ANALOGS

Transport pathways for spermidine (Spd) were characterized in mammalian cells in culture of different origin, i.e. L 1210, P 388, C 6, U 251, Balb/c 3T3 normal and transformed by virus SV40 (SV40/3T3). The kinetic constants (K(m) and V(max)) for 14C-Spd uptake were found to be different in these cells. Spd uptake was inhibited by spermine and putrescine in all cells. Preloading of these cells with system A and other amino acids, including ornithine, usually did not affect Spd uptake, except in L 1210 and C 6 cells, where Spd uptake was accelerated by 2-aminoisobutyric acid, demonstrating that in these two cell lines the polyamines share the system A pathway. Iso-osmotic replacement of Na+ by choline chloride in the assay medium resulted in a decrease in Spd uptake which suggests that Spd uptake is Na+ activated. In all cells, Spd uptake was inhibited by gramicidin and the Ca2+ ionophore A 23187. The degree of inhibition varied among the cells. Valinomycin (K+ ionophore) inhibited Spd uptake by C 6, P 388, Balb/c 3T3 and SV40/3T3 but not by L 1210 and U 251 cells. Treatment with N-ethylmaleimide or p-chloromercuribenzene sulfonate abolished the Spd uptake by U 251 and P 388 cells, while the same treatment to L 1210, C 6, Balb/c 3T3 and SV40/3T3 cells did not affect appreciably the uptake process. Some newly synthesized polyamine analogues inhibited the Spd uptake of all cells.