Mechanisms of sympathoexcitation via P2Y₆ receptors

Many drugs used in cardiovascular therapy, such as angiotensin receptor antagonists and beta-blockers, may exert at least some of their actions through effects on the sympathetic nervous system, and this also holds true for e.g., P2Y₁₂ antagonists. A new target at the horizon of cardiovascular drugs is the P2Y₆ receptor which contributes to the development of arteriosclerosis and hypertension. To learn whether P2Y₆ receptors in the sympathetic nervous system might contribute to actions of respective receptor ligands, responses of sympathetic neurons to P2Y₆ receptor activation were analyzed in primary cell culture. UDP in a concentration dependent manner caused membrane depolarization and enhanced numbers of action potentials fired in response to current injections. The excitatory action was antagonized by the P2Y₆ receptor antagonist MRS2578, but not by the P2Y₂ antagonist AR-C118925XX. UDP raised intracellular Ca²⁺ in the same range of concentrations as it enhanced excitability and elicited inward currents under conditions that favor Cl^- conductances, and these were reduced by a blocker of Ca²⁺-activated Cl^- channels, CaCCInh-A01. In addition, UDP inhibited currents through K_V7 channels. The increase in numbers of action potentials caused by UDP was not altered by the K_V7 channel blocker linopirdine, but was enhanced in low extracellular Cl^- and was reduced by CaCCInh-A01 and by an inhibitor of phospholipase C. Moreover, UDP enhanced release of previously incorporated [3H] noradrenaline, and this was augmented in low extracellular Cl^- and by linopirdine, but attenuated by CaCCInh-A01. Together, these results reveal sympathoexcitatory actions of P2Y₆ receptor activation involving Ca²⁺-activated Cl^- channels.