Nucleotides excite sensory neurons via two P2Y receptors and a dual signaling cascade

Results ADP (EC50: 7.5 μM), ATP (EC50: 0.5 μM), UTP (EC50: 0.8 μM), and thio-UTP (EC50: 0.4 μM) increased the number of action potentials fired in response to current injection; UDP failed to affect action potential firing. The effect of ADP was attenuated by a P2Y1 antagonist. This enhancement of excitability was abolished by flupirtine (30 μM), a KV7 channel opener, and slightly, but insignificantly attenuated by iodoresiniferatoxin (0.3 μM). Under voltage clamp, the same nucleotides inhibited currents through KV7 channels in a concentration-dependent manner with similar EC50 values. The P2Y1-specific agonist MRS2365 also caused an inhibition of KV7 channels (EC50 value of 8.68 nM), and the P2Y1 antagonist MRS2179 attenuated the inhibition by ADP. Treatment of sensory neurons with the phospholipase C inhibitor U73122, with the Ca2+-ATPase inhibitor thapsigargin, or the Ca2+ chelator BAPTA-AM abolished the inhibition of KV7 channels by ADP. Moreover, ADP and ATP increased amplitudes of currents through TRPV1 receptors evoked by capsaicin.