Extracellular nucleotides released from various tissues play a multiple physiological role via activation of purinoceptors. It has been reported that ATP co-secreted with insulin from pancreatic β cells may regulate the insulin release via purinergic receptor activation. In this study, we investigated the effect of extracellular ATP on insulin secretion from iGL cells, the rat insulinoma β-cell line INS-1E, which stably expresses the insulin-Gaussia luciferase fusion protein.
Stimulation of iGL cells with high concentrations of glucose stimulated the co-release of ATP and insulin. Extracellular ATP enhanced insulin secretion in the early phase, but suppressed it in the later phase, in a concentration dependent manner. The inhibition of insulin release by ATP in the later phase was canceled by selective adenosine A₁ receptor antagonist DPCPX and Gi protein inhibitor pertussis toxin. In addition, DPCPX enhanced glucose-induced insulin release, suggesting that endogenous adenosine was involved in the negative regulation of insulin secretion. iGL cells expressed mRNA for ecto-nucleotidase NTPDase3 and CD73. Actually, iGL converted ATP to ADP, AMP and adenosine in time dependent manner. The nucleotide degradation by iGL cells were inhibited by non-selective ecto-nucleotidase inhibitor POM1 and α, β-methylene ADP, a CD73 inhibitor.
These results suggest that ATP co-released with insulin regulates insulin secretion positively in the early phase but negatively in the later phase through the conversion of ATP into adenosine.