Abstract
A variety of
N
ω
-monosubstituted
l-arginine analogs are established inhibitors of nitric oxide synthase; in all cases, initial binding is competitive with the substrate
l-arginine. The efficacy of such compounds in vivo will depend on their transport into the relevant nitric oxide synthase-containing cells; in fact, inhibition may actually be augmented if cellular uptake of
l-arginine is also blocked by the analogs. Because vascular endothelial cells synthesize vasoactive nitric oxide under both physiological and pathophysiological conditions, we have performed inhibition analyses with novel arginine analogs to determine the substrate specificity of the primary
l-arginine transport system, Na
+-independent System y
+, present in porcine pulmonary artery endothelial cells. As reported by others, no Na
+-independent System b
o,+ activity was detectable. For System y
+, Dixon plots suggest competitive inhibition and apparent
K
i values, which ranged between 0.1 and 0.8 mM, were estimated for each inhibitor. Some influence of amino acid side chain structure could be detected, but in general, the data establish that this transport system accepts a broad range of arginine derivatives. Loading the cells with individual arginine analogs resulted in trans-stimulation of arginine uptake suggesting that they serve as substrates of System y
+ as well as inhibitors. These results indicate that plasma membrane transport is unlikely to be a limiting factor in drug development for nitric oxide synthase inhibitors.