Flow does not alter eNOS phosphoryation at Ser1179 or Thr495 in preconstricted mouse mesenteric arteries

In arteries, endothelium-dependent vasodilatory agonists and flow-induced shear stress cause vasodilation largely by activation of the endothelial enzyme eNOS, which generates nitric oxide that relaxes vascular smooth muscle. Agonists activate eNOS in part through increased phosphorylation at Ser1179 and decreased phosphorylation at Thr495. We previously found that preconstriction of intact, isolated mouse mesenteric arteries with phenylephrine also caused increased Ser1179 and decreased Thr495 eNOS phosphorylation, and sequential treatment with the vasodilatory agonist acetylcholine did not cause any further change in phosphorylation at these sites, despite producing vasodilation. The present study tests the hypothesis that luminal flow in these arteries preconstricted with phenylephrine also produces vasodilation without phosphorylation changes at these sites. First-order mesenteric arteries, isolated from male C57/BL6 mice (7-20 weeks of age) anesthetized with pentobarbital (50 mg/kg, i.p.), were cannulated, pressurized, and treated with stepped increases in luminal flow (15-120 μL/min). Flow resulted in dilation that plateaued at ~60 μL/min (31.3 ± 3.0% dilation) and was significantly (P < 0.001) NOS-dependent at all flow rates (determined by 10^-4 mol/L L-NAME treatment). In separate arteries, preconstriction with phenylephrine (10^-5 mol/L) resulted in increased eNOS phosphorylation at Ser1179 (P < 0.05) and decreased phosphorylation at Thr495, but subsequent flow at 60 μL/min for 5 or 15 min did not cause further changes in phosphorylation, despite causing dilation. Thus, flow-induced dilation does not require changes in these eNOS phosphorylation sites beyond those induced by alpha₁-adrenergic stimulation with phenylephrine, indicating that eNOS is activated by other mechanisms during acute flow-induced dilation of preconstricted arteries.