THE HUMAN A1 ADENOSINE RECEPTOR - LIGAND-BINDING PROPERTIES, SITES OFSOMATIC EXPRESSION AND CHROMOSOMAL LOCALIZATION

The Al adenosine receptor (A1AR) exerts important biological effects i n the mammalian biology. To provide insights into the role A1AR action in human physiology, we characterized the pharmacologic properties of the human A1AR, examined somatic sites of A1AR gene expression, and i dentified the chromosomal location of the human A1AR gene. Using stabl y transfected CHO cells, the ligand binding properties of human and ra t A1ARs were directly compared. Saturation studies showed that the hum an and rat A1ARs had similar high affinity for the Al agonist [H-3]CCP A (human, K-d = 517 +/- 64 PM; B-max 438 +/- 29 fmol/mg of protein; ra t, K-d = 429 +/- 69 pM; B-max 358 +/- 76 fmol/mg of protein). Competit ion studies performed using seven adenosine agonists and four adenosin e antagonists also did not detect differences in the ligand binding pr operties among the rat and human A1ARs. Northern analysis of 16 human tissues revealed the presence of a single hybridizing transcript of 2. 5 kb. Human A1AR receptor mRNA expression was greatest in brain and te stis; lower levels of A1AR mRNA were present in heart, pancreas, kidne y and spleen. Southern blotting and PCR analysis of human-rodent somat ic cell hybrids showed that the A1AR gene is on human chromosome 1. Us ing fluorescence in situ hybridization, the human A1AR gene was furthe r localized to the 1q32.1 region. These observations show that the hum an A1AR is a high affinity receptor that has ligand binding properties similar to the rat A1AR, human A1AR mRNA is heavily expressed in brai n and testis, and the gene encoding the human A1AR is present on the l ong arm of chromosome 1.