CLONING AND CHARACTERIZATION OF A PHARMACOLOGICALLY DISTINCT A(1) ADENOSINE RECEPTOR FROM GUINEA-PIG BRAIN

Three full-length cDNA clones encoding the guinea pig A(1) adenosine r eceptor have been isolated by polymerase chain reaction (PCR) and low- stringency hybridization screening of a guinea pig brain cDNA library. These three cDNAs, though differing in their 5' untranslated regions, contain the same open reading frame encoding a 326 amino acid residue protein with seven hydrophobic alpha-helices long enough to form the transmembrane domains, suggesting that it belongs to the G protein-cou pled receptor superfamily. This protein is highly homologous to the A( 1) adenosine receptors previously cloned from other species. Pharmacol ogical characterization of this receptor transiently expressed in mamm alian cells demonstrates that, despite its high homology to A(1) adeno sine receptors of other species, the guinea pig A(1) adenosine recepto r displays a unique pharmacological profile: high affinity for the A(1 )-selective antagonist CPX, yet very low affinity for some A(1)-select ive agonists such as CCPA, CHA and R-PIA. Northern blotting for differ ent guinea pig tissues and in situ hybridization for guinea pig brain sections reveal an abundant and broad distribution of mRNA of this A(1 ) subtype receptor in the brain.