Evidence for the possible involvement of the P2Y6 receptor in Ca2+ mobilization and insulin secretion in mouse pancreatic islets

Subtypes of purinergic receptors involved in modulation of cytoplasmic calcium ion concentration ([Ca(2+)](i)) and insulin release in mouse pancreatic beta-cells were examined in two systems, pancreatic islets in primary culture and beta-TC6 insulinoma cells. Both systems exhibited some physiological responses such as acetylcholine-stimulated [Ca(2+)](i) rise via cytoplasmic Ca(2+) mobilization. Addition of ATP, ADP, and 2-MeSADP (each 100 microM) transiently increased [Ca(2+)](i) in single islets cultured in the presence of 5.5 mM (normal) glucose. The potent P2Y(1) receptor agonist 2-MeSADP reduced insulin secretion significantly in islets cultured in the presence of high glucose (16.7 mM), whereas a slight stimulation occurred at 5.5 mM glucose. The selective P2Y(6) receptor agonist UDP (200 microM) transiently increased [Ca(2+)](i) and reduced insulin secretion at high glucose, whereas the P2Y(2/4) receptor agonist UTP and adenosine receptor agonist NECA were inactive. [Ca(2+)](i) transients induced by 2-MeSADP and UDP were antagonized by suramin (100 microM), U73122 (2 microM, PLC inhibitor), and 2-APB (10 or 30 microM, IP(3) receptor antagonist), but neither by staurosporine (1 microM, PKC inhibitor) nor depletion of extracellular Ca(2+). The effect of 2-MeSADP on [Ca(2+)](i) was also significantly inhibited by MRS2500, a P2Y(1) receptor antagonist. These results suggested that P2Y(1) and P2Y(6) receptor subtypes are involved in Ca(2+) mobilization from intracellular stores and insulin release in mouse islets. In beta-TC6 cells, ATP, ADP, 2-MeSADP, and UDP transiently elevated [Ca(2+)](i) and slightly decreased insulin secretion at normal glucose, while UTP and NECA were inactive. RT-PCR analysis detected mRNAs of P2Y(1) and P2Y(6), but not P2Y(2) and P2Y(4) receptors.