Evidence that rat hepatocytes co‐express functional P2Y1 and P2Y2 receptors

Previous studies have indicated the expression of multiple P2Y receptors by rat hepatocytes although they have not been identified. Here we show by reverse transcriptase‐polymerase chain reaction (RT–PCR) that rat hepatocytes express mRNA encoding all of the four cloned rat P2Y receptors (P2Y1, P2Y2, P2Y4 and P2Y6). The effects of UTP have been examined on single aequorin‐injected rat hepatocytes. The [Ca2+]i transients induced by UTP were indistinguishable from those induced by ATP in the same cell. The modulatory effects of elevated intracellular cyclic AMP concentration were the same on both UTP‐ and ATP‐induced [Ca2+]i transients. UDP, an agonist at the P2Y6 receptor, failed to induce transients in hepatocytes, indicating that functional P2Y6 receptors coupled to increased [Ca2+]i are not expressed. The transients evoked by ADP were more sensitive to inhibition by suramin than those induced by either ATP or UTP. Within an individual cell, the transients induced by ATP and UTP were inhibited by the same concentration of suramin. This sensitivity of ATP and UTP responses to suramin suggests action through P2Y2 rather than P2Y4 receptors. Co‐application of 30 μM pyridoxalphosphate‐6‐azophenyl‐2′,4′‐disulphonic acid (PPADS) caused a decrease in frequency and amplitude of transients induced by ADP. ATP‐ and UTP‐induced transients also displayed a decrease in amplitude in response to addition of PPADS, but this was accompanied by an increase in frequency of transients. In conclusion the data presented here are consistent with the co‐expression of P2Y1 and P2Y2 receptors by rat hepatocytes. British Journal of Pharmacology (2000) 129, 764–770; doi:10.1038/sj.bjp.0703103