Abstract

The NADPH oxidase (Nox) subunits 1, 2 (gp91 phox), and 4 are the major sources for reactive oxygen species (ROS) in vascular tissues. In conditions such as ischemia-reperfusion and hypoxia, both ROS and adenosine are released, suggesting a possible interaction. Our aim in this study was to examine the A₃ adenosine receptor (A₃AR)-induced vascular effects and its relation to ROS and Nox1, 2, and 4 using aortic tissues from wild-type (WT) and A₃AR knockout (A₃KO) mice. The selective A₃AR agonist 2-chloro-N⁶-(3-iodobenzyl)-adenosine-5′-N-methyluronamide (Cl-IBMECA) (10⁻¹⁰–10⁻⁵ M) induced contraction of the aorta from WT but not from A₃KO mice, and this contraction was inhibited by the Nox inhibitor apocynin (10⁻⁵ M) and the ROS scavengers superoxide dismutase-polyethylene glycol and catalase-polyethylene glycol (100 U/ml each). Cl-IBMECA-induced contraction was not affected by the mast cell degranulator compound 48/80 (100 μg/ml) or the stabilizer cromolyn sodium (10⁻⁴ M). In addition, Cl-IBMECA (10⁻⁷ M) increased intracellular ROS generation by 35 ± 14% in WT but not in A₃KO aorta, and this increase was inhibited by apocynin (10⁻⁵ M), diphenyleneiodonium chloride (10⁻⁵ M), and the A₃AR antagonist 3-propyl-6-ethyl-5-[(ethylthio)carbonyl]-2 phenyl-4-propyl-3-pyridine carboxylate (MRS1523) (10⁻⁵ M). Furthermore, Cl-IBMECA selectively increased the protein expression of the Nox2 subunit by 150 ± 15% in WT but not in A₃KO mice without affecting either Nox1 or 4, and this increase was inhibited by apocynin. The mRNA of Nox2 was unchanged by Cl-IBMECA in either WT or A₃KO aortas. In conclusion, A₃AR enhances ROS generation, possibly through activation of Nox2, with subsequent contraction of the mouse aorta.