Endothelin (ET-1), an endogenous
peptide with a prominent role in cutaneous
pain, causes mechanical
hypersensitivity in the rat hind paw, partly through mechanisms involving local release of algogenic molecules in the skin. The present study investigated involvement of cutaneous
ATP, which contributes to
pain in numerous animal models. Pre-exposure of ND7/104 immortalized sensory neurons to ET-1 (30nM) for 10min increased the proportion of cells responding to
ATP (2μM) with an increase in intracellular
calcium, an effect prevented by the ETA receptor-selective antagonist
BQ-123. ET-1 (3nM) pre-exposure also increased the proportion of isolated mouse dorsal root ganglion neurons responding to
ATP (0.2-0.4μM). Blocking ET-1-evoked increases in intracellular
calcium with the
IP3 receptor antagonist 2-APB did not inhibit sensitization to
ATP, indicating a mechanism independent of ET-1-mediated intracellular
calcium increases. ET-1-sensitized
ATP calcium responses were largely abolished in the absence of extracellular
calcium, implicating ionotropic P2X receptors. Experiments using quantitative polymerase chain reaction and receptor-selective
ligands in ND7/104 showed that ET-1-induced sensitization most likely involves the
P2X4 receptor subtype. ET-1-sensitized
calcium responses to
ATP were strongly inhibited by broad-spectrum (
TNP-ATP) and P2X4-selective (5-BDBD) antagonists, but not antagonists for other P2X subtypes.
TNP-ATP and 5-BDBD also significantly inhibited ET-1-induced mechanical sensitization in the rat hind paw, supporting a role for
purinergic receptor sensitization in vivo. These data provide evidence that mechanical
hypersensitivity caused by cutaneous ET-1 involves an increase in the neuronal sensitivity to
ATP in the skin, possibly due to sensitization of P2X4 receptors.