TY - JOUR T1 - Regulation of Rat Hepatocyte Function by P2Y Receptors: Focus on Control of Glycogen Phosphorylase and Cyclic AMP by 2-Methylthioadenosine 5′-Diphosphate JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 334 LP - 341 DO - 10.1124/jpet.104.067744 VL - 311 IS - 1 AU - C. Jane Dixon AU - John F. Hall AU - Tania E. Webb AU - Michael R. Boarder Y1 - 2004/10/01 UR - http://jpet.aspetjournals.org/content/311/1/334.abstract N2 - Hepatocyte function is regulated by several P2Y receptor subtypes. Here we report that 2-methylthioadenosine 5′-diphosphate (2-MeSADP), an agonist at P2Y1, P2Y12, and P2Y13 receptors, potently (threshold 30 nM) stimulates glycogen phosphorylase in freshly isolated rat hepatocytes. Antagonism by N6-methyl 2′-deoxyadenosine 3′,5′-bisphosphate (MRS 2179) confirms that this response is mediated by P2Y1 receptors. In addition, in these cells, both 2-MeSADP and UTP inhibited glucagon-stimulated cyclic AMP accumulation. This inhibitory effect of 2-MeSADP was not reversed by the P2Y1 antagonists, adenosine-3′-phosphate-5′-phosphate (A3P5P) or MRS 2179, both in the range 1 to 300 μM, indicating that it was not mediated by P2Y1 receptors. This contrasts with the increase in cytosolic free Ca2+ concentration ([Ca2+]c) induced by 2-MeSADP, which has shown to be inhibited by A3P5P. Pertussis toxin abolished the inhibitory effect of both UTP and 2-MeSADP. After culture of cells for 48 h, the ability of 2-MeSADP to inhibit cyclic AMP accumulation was greatly diminished. Reverse transcriptase-polymerase chain reaction analysis revealed that during this culture period, there was a decline in the ability to detect transcripts for P2Y12 and P2Y13 receptors, both of which are activated by 2-MeSADP and negatively coupled to adenylyl cyclase. However, in freshly isolated cells, the P2Y12 and P2Y13 receptor antagonist, 2-propylthio-β,γ-dichloromethylene-d-ATP (AR-C67085) (10 nM to 300 μM) did not alter the ability of 2-MeSADP to inhibit glucagon-stimulated cyclic AMP accumulation. We conclude that 2-MeSADP regulates rat hepatocyte glycogen phosphorylase by acting on P2Y1 receptors coupled to raised [Ca2+]c, and by inhibiting cyclic AMP levels by an unknown Gi-coupled receptor subtype, distinct from P2Y1, P2Y12, or P2Y13 receptors. The American Society for Pharmacology and Experimental Therapeutics ER -