Fig. 6.

Endothelial cell delta-like protein-4 (Dll4)-deficient arterial segments exhibit impaired relaxation. A: mesenteric artery (MA) segments from control [vascular endothelial cadherin-Cre^ERT2 (Ve)]⁻/Dll4 flox/flox (Dll4^f/f) and Dll4-deficient (Ve⁺Dll4^def) mice were preconstricted with phenylephrine (PE) and subjected to sodium nitroprusside (SNP, left) and acetylcholine (ACh, right) dose-response experiments. MA segments were subjected to ACh in the presence (dotted lines) or absence (solid lines) of the endothelial NO synthase (eNOS) inhibitor N^ω-nitro-l-arginine methyl ester (l-NAME). Myographic data are displayed as percentages of maximal (max) tension (PE preconstriction) and represent means ± SE (n = 5). Data were analyzed using two-way ANOVA with Bonferroni’s post hoc test [SNP (left): *P < 0.001 and **P < 0.05; ACh (right): solid line comparison, *P < 0.01, **P < 0.001, and ***P < 0.05, and dotted line comparison, #P < 0.05 and ##P < 0.001]. B: wire-mounted aortic (Ao) segments from control (Ve⁻Dll4^f/f) and Dll4-deficient (Ve⁺Dll4^def) mice were preconstricted with PE and subjected to SNP dose-response experiments. Myographic data are displayed as percentages of maximal tension (PE) and represent means ± SE (n = 5). Data were analyzed using two-way ANOVA with Bonferroni’s post hoc test, *P < 0.05. C: control (Ve⁻Dll4^f/f) and Dll4-deficient (Ve⁺Dll4^def) aortas were subjected to arterial myography in the presence or absence of l-NAME. Graphs display PE dose-response curves. Data represent means ± SE (n = 6) and were analyzed using two-way ANOVA with Bonferroni’s post hoc test, *P < 0.001 and **P < 0.01. D: effect of eNOS inhibition on phosphorylated myosin light chain (MLC) levels in constrictor-stimulated aortic rings. Aortic segments from Ve⁻Dll4^f/f and Ve⁺Dll4^def animals were treated with ANG II for 15 min in the presence (+) or absence (−) of l-NAME. Representative immunoblots display phosphorylated MLC (p_MLC) relative to total MLC (T-MLC) and β-actin. Data represent means ± SE of the p-MLC-to-total MLC ratio (n = 4) normalized to (−)l-NAME/(+)ANG II treatment groups. Data were analyzed using a t-test, *P = 0.0187 and **P = 0.0138. Note that in the combined absence of ANG II and l-NAME, no p-MLC signal was detected.