Immunological identification of A 1 adenosine receptors in brain cortex

The A 1 adenosine receptor from pig brain cortex has been identified by means of two antipeptide antibodies against two domains of the receptor molecule: PC/10 antiserum was raised against a part of the third intracellular loop, and PC/20 antiserum was raised against a part of the second extracellular loop. PC/10 antibody was able to recognize a 39‐kDa band that corresponded to the A l receptor, as demonstrated by immunoblotting and by immunoprecipitation of the molecule cross‐linked to [ 125 I](R)‐2‐azidoN 2 ‐p‐hydroxy(phenylisopropyl)adenosine. Besides the 39‐kDa band, PC/20 also recognized a 74‐kDa form that does not seem to correspond to a receptor‐G protein complex. The occurrence of the two bands was detected and analyzed in samples from different species and tissues showing a heterogeneous distribution of both. The 74‐kDa form can be converted into the 39‐kDa form by treatment with agonists or antagonists of A l adenosine receptors. These results suggest that A 1 adenosine receptor can occur in dimers and that the dimer–monomer conversion might be regulated by adenosine as the physiological ligand. Since the 74‐kDa aggregates were not recognized by PC/10, it is likely that part of the third intracellular loop participates in the protein–protein interaction. ©1995 Wiley‐Liss, Inc.