Functional relaxing adenosine receptors in isolated rat tracheal smooth muscle

In the presence of 10-7 M DPCPX (8-Cyclopentyl-1,3-dipropylxanthine, selective antagonist of A1 receptors) adenosine induced relaxing effects on tracheal smooth muscle pre-contracted by K+ (40 mM). The obtained results show that the relaxing effects of adenosine on isolated rat tracheal smooth muscle were associated to adenosine A2 and A3 receptors activation. These results were supported by the use of 10-5 M 8-PT (8-phenyltheophylline or 1,3-Dimethyl-8- phenylxanthine) and 10-6 M VUF5574 {N-(2-Methoxyphenyl)-N′-[2-(3-pyridinyl)-4-quinazo-linyl]-urea}, antagonists for adenosine A2 and, respectively, A3 receptors. The future challenge is related to the deeper characterization of A2 receptor subtype (A2A or A2B) involved in adenosine relaxing effects and of the balance between A2 and A3 receptors in rat tracheal smooth muscle preparations.