Effects of Modulating eNOS Activity on Leukocyte-Endothelial Interactions in Rat Mesenteric Postcapillary Venules

Abstract

Leukocyte‐endothelial interactions associated with vascular injury are attenuated by endothelial‐derived nitric oxide (NO). Endothelial NO synthase (eNOS) in the presence of tetrahydrobiopterin (BH4) produces NO from L‐arginine and is termed eNOS coupling. However, when the ratio of dihydrobiopterin (BH2) to BH4 is increased, eNOS becomes uncoupled and produces superoxide instead of NO. Protein kinase C epsilon (PKC ε) positively regulates eNOS activity. This study examined modulating eNOS activity and coupling by superfusing BH2 (100 μM) by itself, combined with PKC ε activator (10μM) or PKC ε inhibitor (10μM), or combined with BH4 (100μM) and PKC ε activator in rat mesenteric venules. Intravital microscopy was used to evaluate leukocyte endothelial interactions within a 2 hr period. We found that BH2 (100μM n=3, P<0.05) or combined with PKC ε activator (n=5) significantly increased leukocyte rolling, adherence, and transmigration, compared to Krebs’ buffer controls (n=4, P<0.05). By contrast, the combination of PKC ε activator and BH4 significantly attenuated (n=5, P<0.05) BH2 induced leukocyte rolling/adherence. The BH2 induced response on all three leukocyte endothelial interactions was significantly attenuated by PKC ε inhibitor (n=4 P<0.05). The data suggest that promoting eNOS coupling or inhibiting eNOS uncoupling may be important mechanisms mediating inflammation induced vascular injury. .