INHIBITION OF ENDOTHELIAL-CELL AMINO-ACID-TRANSPORT SYSTEM Y(-OXIDE SYNTHASE() BY ARGININE ANALOGS THAT INHIBIT NITRIC)

A variety of N-omega-monosubstituted L-arginine analogs are establishe d inhibitors of nitric oxide synthase; in all cases, initial binding i s competitive with the substrate L-arginine. The efficacy of such comp ounds in vivo will depend on their transport into the relevant nitric oxide synthase-containing cells; in fact, inhibition may actually be a ugmented if cellular uptake of L-arginine is also blocked by the analo gs, Because vascular endothelial cells synthesize vasoactive nitric ox ide under both physiological and pathophysiological conditions, we hav e performed inhibition analyses with novel arginine analogs to determi ne the substrate specificity of the primary L-arginine transport syste m, Na+-independent System y(+), present in porcine pulmonary artery en dothelial cells. As reported by others, no Na+-independent System b(o, +) activity was detectable, For System y(+), Dixon plots suggest compe titive inhibition and apparent K-i values, which ranged between 0.1 an d 0.8 mM, were estimated for each inhibitor, Some influence of amino a cid side chain structure could be detected, but in general, the data e stablish that this transport system accepts a broad range of arginine derivatives, Loading the cells with individual arginine analogs result ed in trans-stimulation of arginine uptake suggesting that they serve as substrates of System y(+) as well as inhibitors. These results indi cate that plasma membrane transport is unlikely to be a limiting facto r in drug development for nitric oxide synthase inhibitors.