A selective agonist radioligand for A adenosine receptors (AARs) is currently not available. Such a tool would be useful for labeling the active conformation of the receptors. Therefore, we prepared BAY 60-6583, a potent and functionally selective AAR (partial) agonist, in a tritium-labeled form. Despite extensive efforts, however, we have not been able to establish a radioligand binding assay using [H]BAY 60-6583. This is probably due to its high non-specific binding and its moderate affinity, which had previously been overestimated based on functional data. As an alternative, we evaluated the non-selective AAR agonist [H]NECA for its potential to label AARs. [H]NECA showed specific, saturable, and reversible binding to membrane preparations of Chinese hamster ovary (CHO) or human embryonic kidney (HEK) cells stably expressing human, rat, or mouse AARs. In competition binding experiments, the AR agonists 2-chloroadenosine (CADO) and NECA displayed significantly higher affinity when tested versus [H]NECA than versus the A-antagonist radioligand [H]PSB-603 while structurally diverse AR antagonists showed the opposite effects. Although BAY 60-6583 is an AAR agonist, it displayed higher affinity versus [H]PSB-603 than versus [H]NECA. These results indicate that nucleoside and non-nucleoside agonists are binding to very different conformations of the AAR. In conclusion, [H]NECA is currently the only useful radioligand for determining the affinity of ligands for an active AAR conformation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.