Reactive 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 a1-adrenoceptor-activated contraction by altering myosin phosphatase activities. Methods: Using 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 a1-adrenoceptor agonist phenylephrine were examined. Results: An antioxidant, N-acetyl-L-cysteine (NAC), and two NADPH oxidase inhibitors, apocynin and VAS2870,. | Tsai and Jiang Journal of Biomedical Science 2010 17 67 http content 17 1 67 NSC The cost of publication in Journal of Biomedical Science Is borne by the National Science Council Taiwan JOURNAL OF BIOMEDICAL SCIENCE RESEARCH Open Access Reactive oxygen species are involved in regulating a1-adrenoceptor-activated vascular smooth muscle contraction Ming-Ho Tsai1 Meei Jyh Jiang1 2 3 Abstract Background Reactive 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 a1-adrenoceptor-activated contraction by altering myosin phosphatase activities. Methods Using 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 a1-adrenoceptor agonist phenylephrine were examined. Results An 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. Conclusions ROS probably derived from .
