ANGIOTENSIN-II STIMULATES SYSTEM Y(+) AND CATIONIC AMINO-ACID TRANSPORTER GENE-EXPRESSION IN CULTURED VASCULAR SMOOTH-MUSCLE CELLS

The effect of angiotensin II (Ang II) on the transport of cationic amino acids has been examined in vascular smooth muscle cells (VSMC) isolated from rat aortae. Ang II stimulated the uptake rates of radiolabeled arginine and lysine in a time- and concentration-dependent manner. The stimulated arginine uptake could be blocked by pretreatments with cycloheximide and actinomycin D or co-treatment with valsartan, an antagonist specific for Ang II receptor subtype-1. The modulation by Ang II was bidirectional as the efflux of arginine was also stimulated, B-fold over basal. Using reverse transcription-coupled polymerase chain reaction methodology, a partial cDNA with 94% sequence identity to that of cationic amino acid transporter subtype-1 (CAT-1) of mouse fibroblasts was obtained from VSMC. This sequence also exhibited 14 base changes compared with the sequence of ecotropic retrovirus receptor (ERR)/CAT-1 from rat hepatoma. Northern analyses with this partial CAT-1 cDNA and CAT-2 cDNA of mouse T-lymphocytes showed that Ang II rapidly stimulated the expression of both CAT-1 and CAT-2 in VSMC. Both signals peaked at 2 h after exposure to Ang II. The CAT-1 signal decayed over the next 6 h to levels 3-fold above basal, which are maintained up until 24 h. The induced CAT-2 mRNA concentration also decayed rapidly but increased again between 16 and 24 h to levels comparable with those observed at 2 h.