Parallel regulation of arginine transport and nitric oxide synthesis by angiotensin II in vascular smooth muscle cells role of protein kinase C

R59949, a diacylglycerol kinase inhibitor, inhibits inducible nitric oxide production through decreasing transplasmalemmal L-arginine uptake in vascular smooth muscle cells

Although diacylglycerol kinase (DGK) is known to be expressed in vascular smooth muscle cell, its functional significance remains to be clarified. We hypothesized that DGK is involved in the pathway of cytokine-induced nitric oxide (NO) production in vascular smooth muscle cells. The purpose of this study was to investigate the effects of R59949, a diacylglycerol kinase inhibitor, on inducible nitric oxide production in vascular smooth muscle cell. Cultured rat aortic smooth muscle cells (RASMCs) were used to elucidate the effects of R59949 on basal and interleukin-1β (IL-1β)-induced NO production. The effects of R59949 on protein and mRNA expression of induced nitric oxide synthase (iNOS) and on transplasmalemmal L-arginine uptake were also evaluated using RASMCs. Treatment of RASMCs with R59949 (10 μM) inhibited IL-1β (10 ng/ml)-induced NO production but not basal NO production. Neither protein nor mRNA expression level of iNOS after stimulation with IL-1β was significantly affected by R59949. Estimated enzymatic activities of iNOS in RASMCs were comparable in the absence and presence of R59949. Stimulation of RASMCs with IL-1β caused a marked increase in transplasmalemmal L-arginine uptake into RASMCs. L-Arginine uptake in the presence of IL-1β was markedly inhibited by R59949, while basal L-arginine uptake was not significantly affected by R59949. Both IL-1β-induced NO production and L-arginine uptake were abolished in the presence of cycloheximide (1 μM). The results indicate that R59949 inhibits inducible NO production through decreasing transplasmalemmal L-arginine uptake. DGK is suggested to be involved in cytokine-stimulated L-arginine transport and regulate its intracellular concentration in vascular smooth muscle cell.

Regulation of CAT: Cationic amino acid transporter gene expression

The majority of mammalian cationic amino acid transport is mediated by the transport system y(+) which facilitates Na(+) independent cationic amino acid (arginine, lysine, & ornithine) transport and Na(+) dependent zwitterionic amino acid (glutamine & homoserine) transport. Other transport systems y(+)L, b(0,+) and B(0,+) also mediate cationic amino acid transport. Their broad substrate specificities and overlapping expression patterns confound biochemical analysis. The isolation of cDNA clones has permitted an analysis of their regulation and opens the opportunity to define the role of each protein in specific cell types. Two genes,Cat1 andCat2 encode transporters with properties similar to the y(+) transport system. Thecat2 gene from the mouse encodes two distinct proteins. mCAT2, and mCAT2A via alternate splicing; each protein has distinctly different transport properties. The regulation of mCAT1, mCAT2 and mCAT2A proteins are reviewed here. The implications of this gene specific regulation on cationic amino acid transport is discussed.