The Nitric Oxide Pathway Is Amplified in Venular vs Arteriolar Cultured Rat Mesenteric Endothelial Cells

Abstract

To determine if there are differences in nitric oxide activity between pre- and postcapillary microvessels, we studied cultured rat mesenteric arteriolar and venularendothelial cells (RMAEC, RMVEC). We measured expression of endothelial nitric oxide synthase (eNOS), the activity of eNOS, and l-arginine transport in live RMAEC and RMVEC and the l-arginine content of RMAEC and RMVEC lysates. The abundance of eNOS was significantly greater in RMVEC vs RMAEC; this was also true for freshly harvested, pooled microvessels. Baseline NOS activity was higher in RMVEC than in RMAEC. NG-Monomethyl-l-arginine (l-NMA; 5 mM) inhibited NOS activity by ∼70–80% in both RMAEC and RMVEC, indicating that metabolism of l-arginine is largely via NOS. Intracellular l-arginine levels were higher in RMVEC vs RMAEC and well above the eNOS Km in both cell types. l-Arginine levels increased with l-NMA in both RMAEC and RMVEC, presumably due to reduced substrate utilization. Since l-arginine transport was not higher in RMVEC vs RMAEC, this may reflect higher intracellular arginine synthesis. A higher intrinsic level of baseline NO production in the postcapillary microvascular endothelium may reflect both the contribution of venular derived NO to control of arteriolar tone and a key role of venular-derived NO in local thrombosis control.