Possible involvement of A2A and A3 receptors in modulation of insulin secretion and ß-cell survival in mouse pancreatic islets.

ABSTRACT

Adenosine A1, A2A, A2B and A3 receptor mRNAs were found to be expressed in mouse pancreatic islets and Beta-TC6 cells but their physiological or pharmacological actions are not fully clarified. We showed that adenosine (100 µM) augmented insulin secretion by islets in the presence of either normal (5.5 mM) or a high concentration of glucose (20 mM). The augmentation of insulin secretion in the presence of high glucose was blocked by an A2A antagonist, but not by A2B and A3 antagonists, while an A1 antagonist potentiated the adenosine effect. An adenosine analogue 5'-N-ethylcarboxamidoadenosine (NECA) as well as A1, A2A and A3 receptor agonists also produced stimulation. On the other hand, an A3 agonist markedly reduced Beta-TC6 cell proliferation and the islet cell viability, while adenosine and NECA did not. The effect of A3 agonist was partially blocked by the A3 antagonist. In addition, treatment with the A3 agonist produced a small but significant extent of apoptosis in Beta-TC6 cells as judged by terminal transferase-mediated deoxyuridine triphosphate nick end labeling (TUNEL) assay. These results combined together suggested that like the A1 receptor, activation of A2A receptors by adenosine results in augmented insulin secretion, while the A3 receptor is involved in modulation of the survival of pancreatic ß-cells.