Purine receptors in trachea: studies with adenosine deaminase and dipyridamole.

ATP, adenosine, adenine and inosine exhibited similar potency in relaxing transverse strips of guinea-pig trachea. Dipyridamole potentiated responses to ATP and adenosine equally but antagonized responses to inosine and failed to affect responses to adenine. In dipyridamole-treated preparations, adenosine deaminase markedly reduced responses to ATP and adenosine; responses to adenine and inosine were unaffected. The results suggest that ATP acts via its adenosine metabolite and that inhibitory ATP receptors are absent.