Molecular cloning of the rat A 2 adenosine receptor: selective co-expression with D 2 dopamine receptors in rat striatum

Abstract

A cDNA fragment homologous to other G protein-coupled receptors was isolated from rat brain using the PCR method and demonstrated to be abundantly expressed in striatum. Using this fragment as a probe, a 2.1 kb full-length cDNA was isolated from a rat striatal cDNA library. This cDNA encodes a protein of 410 amino acids and is highly homologous to previously isolated adenosine receptor cDNAs. Expression of this cDNA in COS cells revealed high affinity ( K d = 38.6 nM) and saturable binding of the A 2 adenosine receptor-selective ligand [ 3H]CGS 21680. Agonist displacement profile of [ 3H]CGS 21680 binding was consistent with an adenosine receptor of the A 2 subtype (NECA > ( R)- PIA > CPA > ( S)- PIA). In situ hybridization demonstrated that rat A 2 adenosine receptor mRNA was co-expressed in the same striatal neurons as D 2 dopamine receptor mRNA, and never co-expressed with striatal D 1 dopamine receptor mRNA. Several lines of evidence have previously suggested that dopamine-induced changes in motor behavior can be modulated by adenosine analogs acting at the A 2 subtype of adenosine receptor in the forebrain. The co-expression of D 2 dopamine and A 2 adenosine receptors in a subset of striatal cells provides an anatomical basis for dopaminergic-adenosinergic interactions on motor behavior.