Induction of cationic amino acid transport activity in mouse peritoneal macrophages by lipopolysaccharide

The transport of cationic amino acids has been investigated in mouse peritoneal macrophages cultured in vitro. The transport activity for lysine was rather low in cells cultured for 1 h and increased slightly in cells cultured for 12 h. This increase varied with the serum lot used in the culture medium and was suppressed by polymyxin B, suggesting that the transport activity is induced by endotoxins in the serum. When the macrophages were cultured in the medium containing 1 ng/ml lipopolysaccharide, the transport activity for lysine increased by more than 10-fold. The transport activity for lysine induced by lipopolysaccharide has been characterized. Lysine was transported mainly by a Na(+)-independent, saturable system. The uptake of lysine was potently inhibited by extracellular cationic amino acids, but not by neutral amino acids tested. In addition, transport of lysine showed trans-stimulation. From these results, we have concluded that the transport activity for cationic amino acids is potently induced by lipopolysaccharide and that the characteristics of the induced activity is consistent with those of system y+.