Desensitisation of the Adenosine A1 Receptor by the A2A Receptor in the Rat Striatum

The influence of the adenosine A2A receptor on the A1 receptor was examined in rat striatal nerve terminals, a model for other cells in which these receptors are coexpressed. Incubation of striatal synaptosomes with the A2A receptor agonist 2-p-(2-carboxyethyl)phenethylamino-5'-N-ethylcarboxamidoadenosine (CGS 21680) caused the appearance of a low-affinity binding site for the A1 receptor agonist 2-chloro-N6-cyclopentyladenosine (CCPA). This effect was blocked by the A2A receptor antagonist ZM241385 and by the protein kinase C inhibitor chelerythrine, but not by the protein kinase A inhibitor N-(2-guanidinoethyl)-5-isoquinolinesulfonamide (HA 1004). The effect was not seen with striatal membranes or with hypotonically lysed synaptosomes. These results demonstrate a protein kinase C-mediated heterologous desensitisation of the A1 receptor by the A2A receptor.