Reactive oxygen species are involved in regulating α1-adrenoceptor-activated vascular smooth muscle contraction

Abstract

BackgroundReactive oxygen species (ROS) were shown to mediate aberrant contractility in hypertension, yet the physiological roles of ROS in vascular smooth muscle contraction have remained elusive. This study aimed to examine whether ROS regulate α1-adrenoceptor-activated contraction by altering myosin phosphatase activities.MethodsUsing endothelium-denuded rat tail artery (RTA) strips, effects of anti-oxidants on isometric force, ROS production, phosphorylation of the 20-kDa myosin light chain (MLC20), and myosin phosphatase stimulated by α1-adrenoceptor agonist phenylephrine were examined.ResultsAn antioxidant, N-acetyl-L-cysteine (NAC), and two NADPH oxidase inhibitors, apocynin and VAS2870, dose-dependently inhibited contraction activated by phenylephrine. Phenylephrine stimulated superoxide anion production that was diminished by the pretreatment of apocynin, VAS2870, superoxide scavenger tiron or mitochondria inhibitor rotenone, but not by xanthine oxidase inhibitor allopurinol or cyclooxygenase inhibitor indomethacin. Concurrently, NADPH oxidase activity in RTA homogenates increased within 1 min upon phenylephrine stimulation, sustained for 10 min, and was abolished by the co-treatment with apocynin, but not allopurinol or rotenone. Phenylephrine-induced MLC20 phosphorylation was dose-dependently decreased by apocynin. Furthermore, apocynin inhibited phenylephrine-stimulated RhoA translocation to plasma membrane and phosphorylation of both myosin phosphatase regulatory subunit MYPT1Thr855 and myosin phosphatase inhibitor CPI-17Thr38.ConclusionsROS, probably derived from NADPH oxidase and mitochondria, partially regulate α1-adrenoceptor-activated smooth muscle contraction by altering myosin phosphatase-mediated MLC20 phosphorylation through both RhoA/Rho kinase- and CPI-17-dependent pathways.

Enhanced Vascular Neuronal Nitric-Oxide Synthase-Derived Nitric-Oxide Production Underlies the Pressor Response Caused by Peripheral N-Methyl-d-Aspartate Receptor Activation in Conscious Rats

“…Furthermore, in agreement with findings that PE-evoked contraction is associated with increased vascular ROS (Hao et al, 2006;Tsai and Jiang, 2010), we showed that PEevoked pressor response was associated with ex vivo vascular ROS generation. Nonetheless, it was imperative to affirm a causal role for the NO-ROS cascade in the peripheral NMDAR-mediated pressor response.…”

The NADPH Oxidase Family and its Inhibitors

“…Moreover, apocynin administration to mice with hereditary hypertension normalized blood pressure, catecholamines, H 2 O 2 , isoprostane, and NO concentration (Gayen et al 2010). Similar results were obtained by Tsai and Jiang (2010), where apocynin and VAS-2870 decreased phenylephrine-induced superoxide anion production.…”

Lidocaine relaxation in isolated rat aortic rings is enhanced by endothelial removal: possible role of Kv, KATP channels and A2a receptor crosstalk

“…Enhanced lidocaine relaxation may also have come from changing the cellular redox state and reactive oxygen species (ROS) derived from NAD(P)H oxidases [55, 56], as it has been reported that lidocaine at higher concentrations protects against ROS attack in rabbit abdominal aorta [9]. Rogers and colleagues further showed that 4-AP-sensitive K v channels are redox sensitive and contribute to H 2 O 2 -induced coronary vasodilation [57].…”