Nucleotides control the excitability of sensory neurons via two P2Y receptors and a bifurcated signaling cascade

Abstract

Nucleotides contribute to the sensation of acute and chronic pain, but it remained enigmatic which G protein-coupled nucleotide (P2Y) receptors and associated signaling cascades are involved. To resolve this issue, nucleotides were applied to dorsal root ganglion neurons under current- and voltage-clamp. Adenosine triphosphate (ATP), adenosine diphosphate (ADP), and uridine triphosphate (UTP), but not uridine diphosphate (UDP), depolarized the neurons and enhanced action potential firing in response to current injections. The P2Y2 receptor preferring agonist 2-thio-UTP was equipotent to UTP in eliciting these effects. The selective P2Y1 receptor antagonist MRS2179 largely attenuated the excitatory effects of ADP, but left those of 2-thio-UTP unaltered. Thus, the excitatory effects of the nucleotides were mediated by 2 different P2Y receptors, P2Y1 and P2Y2. Activation of each of these 2 receptors by either ADP or 2-thio-UTP inhibited currents through KV7 channels, on one hand, and facilitated currents through TRPV1 channels, on the other hand. Both effects were abolished by inhibitors of phospholipase C or Ca2+-ATPase and by chelation of intracellular Ca2+. The facilitation of TRPV1, but not the inhibition KV7 channels, was prevented by a protein kinase C inhibitor. Simultaneous blockage of KV7 channels and of TRPV1 channels prevented nucleotide-induced membrane depolarization and action potential firing. Thus, P2Y1 and P2Y2 receptors mediate an excitation of dorsal root ganglion neurons by nucleotides through the inhibition of KV7 channels and the facilitation of TRPV1 channels via a common bifurcated signaling pathway relying on an increase in intracellular Ca2+ and an activation of protein kinase C, respectively.