Thrombin induces a temporal biphasic vascular response through the differential phosphorylation of endothelial nitric oxide synthase via protease-activated receptor-1 and protein kinase C.

Endothelial nitric oxide synthase (eNOS) is a critical regulatory enzyme that controls vascular tone via the production of nitric oxide. Although thrombin also modulates vascular tone predominantly via the activation of protease-activated receptors (PARs), the time course and mechanisms involved in how thrombin controls eNOS enzymatic activity are unknown. eNOS enzymatic activity is enhanced by the phosphorylation of eNOS-Ser1177 and reduced by the phosphorylation of eNOS-Thr495. In this study, we hypothesized that thrombin regulates vascular tone through the differential phosphorylation of eNOS. Using rat descending aorta, we show that thrombin modulates vascular tone in an eNOS-dependent manner via activated PAR-1. We also show that thrombin causes a temporal biphasic response. Protein kinase C (PKC) is associated with second phase of thrombin-induced response. Western blot analysis demonstrated thrombin phosphorylated eNOS-Ser1177 and eNOS-Thr495 in human umbilical vein endothelial cells. A PKC inhibitor suppressed the thrombin-induced phosphorylation of eNOS-Thr495, but not that of eNOS-Ser1177. Our results suggest that thrombin induces a temporal biphasic vascular response through the differential phosphorylation of eNOS via activated PAR-1. Thrombin causes transient vasorelaxation by the phosphorylation of eNOS-Ser1177, and subsequent attenuation of vasorelaxation by the phosphorylation of eNOS-Thr495 via PKC, leading to the modulation of vascular tone.