Our previous study demonstrated that adenine (6-amino-6H-purine) relaxed contracted rat aorta rings in an endothelial-independent manner. Although adenine receptors (AdeRs) are expressed in diverse tissues, aortic AdeR expression has not been ascertained. Thus, the aims of this study were to clarify the expression of AdeR in rat vascular smooth muscle cells (VSMCs) and to investigate the adenine-induced vasorelaxation mechanism(s). VSMCs were isolated from 8-week-old male Wistar-Kyoto rats and used in this study. Phosphorylation of myosin light chain (p-MLC) was measured by western blot. AdeR mRNA was detected by RT-PCR. Intracellular Ca2+ concentration ([Ca2+]i) was measured by using Fura-2/AM. Vasorelaxant adenine (10–100 μM) significantly reduced p-MLC by angiotensin II (Ang II, 10 μM) in VSMCs (P < 0.05). We confirmed the expression of aortic AdeR mRNA and the activation of PKA in VSMCs through stimulation of AdeR by adenine by ELISA. Intracellular Ca2+ concentration ([Ca2+]i) measurement demonstrated that adenine inhibits Ang II- and m-3M3FBS (PLC agonist)-induced [Ca2+]i elevation. In AdeR-knockdown VSMCs, PKA activation and p-MLC reduction by adenine were completely abolished. These results firstly demonstrated that vasorelaxant adenine can suppress Ca2+ contraction signaling pathways via aortic AdeR/PKA activation in VSMCs.
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