Abstract
The intracellular signaling pathways involved in the activation of P2Y receptor-mediated Cl− currents (ICl,P2Y) were studied in mouse ventricular myocytes with the whole-cell clamp method. With high concentrations of EGTA in the pipette, extracellular application of UTP (0.1-100 μM) elicited a Cl− current which showed a time-independent activation during step voltages and a linear I-V relationship in symmetrical Cl− solutions. Its anion selectivity was Cl− > I− > Asp−. The potency of UTP (EC50 = ∼1 μM) for the current activation was almost equal to that of ATP, while ADP and UDP were less potent. Suramin, but not PPADS, inhibited the activation of ICl,P2Y. These data suggest that the P2Y-receptor subtype involved is P2Y2. The activation of ICl,P2Y by UTP was suppressed by extracellular application of PLC inhibitors or intracellular dialysis of anti-Gαq/11 antibody, while the suppression was relieved by application of PKC activators. These results suggest that the UTP activates ICl,P2Y through Gq/11-coupled P2Y2 receptor-PLC-PKC signaling. When the cells were dialyzed with non-hydrolyzable ATP analogues (ATPγS or AMP-PNP) without ATP, UTP failed to activate ICl,P2Y, whereas ICl,P2Y was persistently activated by UTP in the cells dialyzed with both ATP and ATPγS, suggesting that phosphorylation and ATP hydrolysis are involved in the activation of ICl,P2Y. The Gαq/11-PLC-PKC signaling and intracellular ATP hydrolysis may be the essential mechanisms for the activation of ICl,P2Y by UTP in cardiac cells. [Jpn J Physiol 55 Suppl:S89 (2005)]
