The binding characteristics of radiolabeled N-6-(cyclohexyl)adenosine ([H-3]CHA), N-6-(R-phenylisopropyl)adenosine ([H-3]R-PIA), 5'-N-ethyl-carboxamidoadenosine ([H-3]NECA), and 2-[4-(2-carboxyethyl)phenyl]ethyl-amino-5'-N-ethylcarboxamidoadenosine ([H-3]CGS 21680), to rat testis membranes were investigated. Specific binding of [H-3]CGS 21680, a selective agonist for the A(2a) adenosine receptor, was very modest whilst the nonselective agonist [H-3]NECA bound to rat testis membranes showing high binding capacity. At least two types of binding sites for [H-3]NECA could be identified in rat testis membranes: high affinity sites and high capacity sites. Selective agonists for the A(1) adenosine receptor, [H-3]CHA and [H-3]R-PIA bound with high affinity to a single class of binding sites. This high affinity binding site showed the typical pharmacological specificity of the A(1) adenosine receptor with a potency order fur agonists of CHA greater than or equal to R-PIA greater than or equal to NECA greater than or equal to N-6-(S-phenylisopropyl)adenosine (S-PIA). In order to detect the presence of the A(3) adenosine receptor in these membranes we selectively blocked the A(1) receptor with a large molar excess of a xanthine antagonist, either 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) or xanthine amine congener (XAC). In the presence of an antagonist a low affinity binding site for [H-3]CHA and [H-3]R-PIA was detected. This low affinity binding site showed a different pharmacological specificity than the high affinity binding site. In fact the potency order for agonists was CHA greater than or equal to NECA = R-PIA > S-PIA. This finding suggests that the low affinity binding site represents the A(3) adenosine receptor.
|Autori:||Mazzoni MR; Buffoni RS; Giusti L; Lucacchini A|
|Titolo:||Characterization of a low affinity-binding site for N-6-substituted adenosine derivatives in rat testis membranes|
|Anno del prodotto:||1995|
|Digital Object Identifier (DOI):||10.3109/10799899509049864|
|Appare nelle tipologie:||1.1 Articolo in rivista|