Role of purinergic P2Y1 receptors in regulation of vasopressin and oxytocin secretion.

Pharmacological studies demonstrated that ATP elevates intracellular calcium ([Ca(2+)](i)) in supraoptic nucleus (SON) neurons primarily by activation of P2X2 and P2Y1 purinergic receptors [P2Y1R]. The current studies provide evidence for the presence of P2Y1R protein in SON neurons, evidence that activation of these P2Y1Rs induces an increase in [Ca(2+)](i) from both intracellular stores and Ca(2+) influx, and functional evidence that activation of P2Y1Rs induces vasopressin (VP) and oxytocin (OT) hormone release. Pretreatment of Fura-2 AM-loaded explants of the hypothalamo-neurohypophyseal system (HNS) with thapsigargin (TG) significantly (approximately 80%) reduced the increase in [Ca(2+)](i) induced by the P2Y1R-specific agonist, 2-methylthio-ADP (2-MeSADP). In contrast, the increase in [Ca(2+)](i) was slightly (approximately 20%) decreased in calcium-free medium. The calcium response to 2-MeSADP was completely blocked by the P2Y1R-specific antagonist, MRS2179 or by a combination of TG pretreatment and calcium-free medium. It was absent in P2Y1R knockout mice (P2Y1R(-/-)). 2-MeSADP significantly increased VP and OT release from perifused rat and wild-type mouse HNS explants compared with control. MRS2179 prevented this response in wild-type mouse, but it did not prevent ATP-induced hormone release from rat explants. 2-MeSADP did not induce hormone release from P2Y1R(-/-) explants. These findings support a potential role for P2Y1Rs in regulation of VP and OT release. The finding that P2Y1R activation induces a small Ca(2+) influx suggests that P2Y1Rs may regulate VP release by modifying ion channels such as stretch-inactivated cation channels.