Inhibitory effects of various amino acids and a specific inhibitor on [³H]-l-arginine uptake by K562 cells. (A) Inhibition of [³H]-l-arginine uptake in K562 cells by 1 mM l-arginine, l-lysine, l-ornithine, l-histidine, l-valine, and l-leucine was examined at 37°C for 3 minutes. Data represent means of 4 experiments, and error bars indicate SE. (B) Inhibition of [³H]-l-arginine uptake in K562 cells by the CAT-specific inhibitor NEM was examined at 37°C for 3 minutes after preincubation with NEM for 5 minutes. Data represent means of 4 experiments, and error bars indicate SE.