Cytokines and Insulin Induce Cationic Amino Acid Transporter (CAT) Expression in Cardiac Myocytes

Cytokine-dependent production of nitric oxide (NO) by rat cardiac myocytes is a consequence of increased expression of the inducible isoform of nitric oxide synthase (iNOS or NOS2) and, in the presence of insulin, depresses the contractile function of these cells in vivo and in vitro. Experiments reported here show that L-lysine, a competitive antagonist of L-arginine uptake, suppressed NO production (detected as nitrite accumulation) by interleukin (IL)-1β and interferon (IFN) -pretreated cardiac myocytes by 70%, demonstrating that NO production is dependent on L-arginine uptake. Cardiac myocytes constitutively exhibit a high-affinity L-arginine transport system (K = 125 μM; V = 44 pmol/2 × 105 cells/min). Following a 24-h exposure to IL-1β and IFN, arginine uptake increases (V = 167 pmol/2 × 105 cells/min) and a second low-affinity L-arginine transporter activity appears (K = 1.2 mM). To examine the molecular basis for these cytokine-induced changes in arginine transport, we examined expression of three related arginine transporters previously identified in other cell types. mRNA for the high-affinity cationic amino acid transporter-1 (CAT-1) is expressed in resting myocytes and steady-state levels increase by 10-fold following exposure to IL-1β and IFN. Only cytokine-pretreated myocytes expressed a second high-affinity L-arginine transporter, CAT-2B, as well as a low-affinity L-arginine transporter, CAT-2A. In addition, insulin, which potentiated cytokine-dependent NO production independent of any change in NOS activity, increased myocyte L-arginine uptake by 2-fold and steady-state levels of CAT-1, but not CAT-2A or CAT-2B mRNA. Thus, NO production by cardiac myocytes exposed to IL-1β plus IFN appears to be dependent on the co-induction of CAT-1, CAT-2A, and CAT-2B, while insulin independently augments L-arginine transport through CAT-1.