Species Comparison of Adenosine Receptor Subtypes in Brain and Testis

摘要

We aimed at comparing the binding characteristics of adenosine A1 and A2A receptors (A1Rs and A2ARs) in high-expressing cerebral areas, the cortex and striatum respectively, of human, bovine and rat brain. Adenosine A3 receptor (A3R) binding was studied in rat and bovine testis. Results confirmed species differences in AR saturation-displacement binding parameters. To investigate A3Rs in CNS, we carried out immunoblot in human brain, resolving two signals, a 52 KDa band with the highest density in hippocampus and a 48 KDa one, slightly more expressed in cortex. Subsequently, A3R binding was performed by [125I]-4-aminobenzyl-5′-N-methylcarboxamidoadenosine ([125I]-AB-MECA) in human hippocampus, revealing an high affinity population of sites and another non saturable component. [125I]-AB-MECA first site displacement by N6 (3-iodobenzyl)adenosine-5′-N-methyluronamide (IB-MECA) and 1,3-dipropyl-8-cyclopenthyl-xanthine (DPCPX) distinguished two affinity sites, being only in part identified as A3Rs. Therefore, A3Rs result clearly expressed by Western blot in human brain, but their full CNS characterization needs further investigation.