CHARACTERIZATION OF SYSTEM-L AND SYSTEM-Y-ACID-TRANSPORT ACTIVITY IN CULTURED VASCULAR SMOOTH-MUSCLE CELLS( AMINO)

The uptake of L-leucine and L-lysine into vascular smooth muscle cells cultured from the aortas of rats has been investigated. Both amino ac ids are taken up by saturable systems that are independent of the pres ence of a Na+ gradient and can be stimulated in trans by neutral bulky amino acids for leucine and cationic amino acids for lysine. Leucine uptake is inhibited competitively in cis by several neutral amino acid s, whereas lysine uptake is inhibited strongly by other cationic amino acids but also significantly by neutral amino acids such as leucine. The leucine inhibition is noncompetitive. Cells preloaded with leucine and lysine could also export these amino acids and the rate of efflux was stimulated by the presence of appropriate amino acids in trans. T hese data are all consistent with leucine being transported largely if not entirely by System L and lysine by the System y+ transporter. (C) 1993 Wiley-Liss, Inc.