Adenosine Can Mediate its Actions through Generation of Reactive Oxygen Species

Abstract

Adenosine is an important cerebral vasodilator, but mediating mechanisms are not understood. We investigated the expression of adenosine receptor subtypes in isolated cerebral arterial muscle cells (CAMCs), and their role in adenosine-induced superoxide (O2−) generation and reduction in cerebral arterial tone. Reverse transcriptase-PCR, western blotting, and immunofluorescence studies have shown that CAMCs express transcript and protein for A1, A2A, A2B, and A3 adenosine receptors. Stimulation of CAMCs with adenosine or the A2A agonist CGS-21680 increased the generation of O2− that was attenuated by the inhibition of A2A and A2B adenosine receptor subtypes, or by the peptide inhibitor of nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase gp91ds-tat, or by the mitochondria uncoupler 2,4-dinitrophenol. Application of adenosine or CGS-21680 dilated pressure-constricted cerebral arterial segments that were prevented by the antioxidants superoxide dismutase (SOD) conjugated to polyethylene glycol (PEG) and PEG-catalase or by the A2B adenosine receptor antagonist MRS-1754, or by the mixed A2A and A2B antagonist ZM-241385. Antagonism of the A2A and A2B adenosine receptors had no effect on cerebral vasodilatation induced by nifedipine. These findings indicate that adenosine reduces pressure-induced cerebral arterial tone through stimulation of A2A and A2B adenosine receptors and generation of O2− from NADPH oxidase and mitochondrial sources. This signaling pathway could be one of the mediators of the cerebral vasodilatory actions of adenosine.