Reactive oxygen species are involved in regulating alpha1-adrenoceptor-activated vascular smooth muscle contraction.
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 alpha1-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 alpha1-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 NADPH oxidase and mitochondria, partially regulate alpha1-adrenoceptor-activated smooth muscle contraction by altering myosin phosphatase-mediated MLC20 phosphorylation through both RhoA/Rho kinase- and CPI-17-dependent pathways.
Tsai
Ming-Ho
MH
Institute of Basic Medical Sciences, College of Medicine, National Cheng Kung University, Tainan 70101, Taiwan.
Jiang
Meei Jyh
MJ
D000098:Acetophenones / Q000494:pharmacology; D000111:Acetylcysteine / Q000494:pharmacology; D058646:Adrenergic alpha-1 Receptor Agonists; D000704:Analysis of Variance; D000818:Animals; D001583:Benzoxazoles / Q000494:pharmacology; D015153:Blotting, Western; D004305:Dose-Response Relationship, Drug; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000502:physiology*; D043263:Myosin-Light-Chain Phosphatase / Q000378:metabolism*; D009218:Myosins / Q000378:metabolism*; D019255:NADPH Oxidases / Q000037:antagonists & inhibitors; D010656:Phenylephrine / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D051381:Rats; D017382:Reactive Oxygen Species / Q000378:metabolism*; D018340:Receptors, Adrenergic, alpha-1 / Q000378:metabolism*; D014230:Triazoles / Q000494:pharmacology; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D020742:rhoA GTP-Binding Protein / Q000378:metabolism
C511179:3-benzyl-7-(2-benzoxazolyl)thio-1,2,3-triazolo(4,5-d)pyrimidine; D000098:Acetophenones; D058646:Adrenergic alpha-1 Receptor Agonists; D001583:Benzoxazoles; D017382:Reactive Oxygen Species; D018340:Receptors, Adrenergic, alpha-1; D014230:Triazoles; D014662:Vasoconstrictor Agents; D010656:Phenylephrine; C056165:acetovanillone; D019255:NADPH Oxidases; D043263:Myosin-Light-Chain Phosphatase; D009218:Myosins; D020742:rhoA GTP-Binding Protein; D000111:Acetylcysteine