Receptor for adenosine. The activity of this receptor is mediated by G proteins which inhibits adenylyl cyclase. Phosphorylation on Thr-317 and Thr-318 may be crucial for rapid desensitization. Phosphorylation on Thr-317 may be necessary for phosphorylation on Thr-318 to occur. Belongs to the G-protein coupled receptor 1 family.