Potentiation of P2X3 receptor mediated currents by endothelin-1 in rat dorsal root ganglion neurons.

Endothelin-1 (ET-1), an endogenous vasoconstrictor, has been known as a pro-nociceptive agent involved in multitude of pain. ET-1 acts on endothelin receptors on vascular endothelial cells, sensitizes release of ATP, which then acts on P2X3 receptors on nociceptors and results in mechanical hyperalgesia. Both endothelin receptors and P2X3 receptors are present in primary sensory neuron, where it remains unclear whether there is an interaction between them. Herein, we reported that ET-1 potentiated the electrophysiological activity of P2X3 receptors in rat dorsal root ganglia (DRG) neurons. ET-1 concentration-dependently increased α,β-methylene-ATP (α,β-meATP)-evoked inward currents, which were mediated by P2X3 receptors. ET-1 shifted the α,β-meATP concentration-response curve upwards, with an increase of 34.38 ± 4.72% in the maximal current response to α,β-meATP in the presence of ET-1. ET-1 potentiation of α,β-meATP-evoked currents was voltage-independent. ET-1 potentiated P2X3 receptor-mediated currents through endothelin-A receptors (ETAR), but not endothelin-B receptors (ETBR). ET-1 potentiation was supressed by blockade of intracellular G-protein or protein kinase C (PKC) signaling. Moreover, there is a synergistic effect on mechanical allodynia induced by intraplantar injection of ET-1 and α,β-meATP in rats. Pharmacological blockade of P2X3 receptors also alleviated ET-1-induced mechanical allodynia. These results suggested that ET-1 sensitized P2X3 receptors in primary sensory neurons via an ETAR and PKC signaling pathway. Our data provide evidence that cutaneous ET-1 induced mechanical allodynia not only by increasing the release of ATP from vascular endothelial cells, but also by sensitizing P2X3 receptors on nociceptive DRG neurons.

Jin Y ，Qiu CY ，Wei S ，Han L ，Liu TT ，Hu WP ... -  《-》

Suppression of P2X3 receptor-mediated currents by the activation of α(2A) -adrenergic receptors in rat dorsal root ganglion neurons.

The α2 -adrenergic receptor (α2 -AR) agonists have been shown to be effective in the treatment of various pain. For example, dexmedetomidine (DEX), a selective α2A -AR agonist, can be used for peripheral analgesia. However, it is not yet fully elucidated for the precise molecular mechanisms. P2X3 receptor is a major receptor processing nociceptive information in primary sensory neurons. Herein, we show that a functional interaction of α2A -ARs and P2X3 receptors in dorsal root ganglia (DRG) neurons could contribute to peripheral analgesia of DEX. Electrophysiological recordings were carried out on rat DRG neurons, and nociceptive behavior was quantified in rats. The activation of α2A -ARs by DEX suppressed P2X3 receptor-mediated and α,β-methylene-ATP (α,β-meATP)-evoked inward currents in a concentration-dependent and voltage-independent manner. Pre-application of DEX shifted the α,β-meATP concentration-response curve downwards, with a decrease of 50.43 ± 4.75% in the maximal current response of P2X3 receptors to α,β-meATP in the presence of DEX. Suppression of α,β-meATP-evoked currents by DEX was blocked by the α2A -AR antagonist BRL44408 and prevented by intracellular application of the Gi/o protein inhibitor pertussis toxin, the adenylate cyclase activator forskolin, and the cAMP analog 8-Br-cAMP. DEX also suppressed α,β-meATP-evoked action potentials through α2A -ARs in rat DRG neurons. Finally, the activation of peripheral α2A -ARs by DEX had an analgesic effect on the α,β-meATP-induced nociception. These results suggested that activation of α2A -ARs by DEX suppressed P2X3 receptor-mediated electrophysiological and behavioral activity via a Gi/o proteins and cAMP signaling pathway, which was a novel potential mechanism underlying analgesia of peripheral α2A -AR agonists.

Hao JW ，Qiao WL ，Li Q ，Wei S ，Liu TT ，Qiu CY ，Hu WP ... -  《-》

Prokineticin 2 facilitates mechanical allodynia induced by α,β-methylene ATP in rats.

Prokineticin 2 (PK2), a new chemokine, causes mechanical hypersensitivity in the rat hind paw, but little is known about the molecular mechanism. Here, we have found that ionotropic P2X receptor is essential to mechanical allodynia induced by PK2. First, intraplantar injection of high dose (3 or 10 pmol) of PK2 significantly increased paw withdrawal response frequency (%) to innocuous mechanical stimuli (mechanical allodynia). And the mechanical allodynia induced by PK2 was prevented by co-administration of TNP-ATP, a selective P2X receptor antagonist. Second, although low dose (0.3 or 1 pmol) of PK2 itself did not produce an allodynic response, it significantly facilitated the mechanical allodynia evoked by intraplantar injection of α,β-methylene ATP (α,β-meATP). Third, PK2 concentration-dependently potentiated α,β-meATP-activated currents in rat dorsal root ganglion (DRG) neurons. Finally, PK2 receptors and intracellular signal transduction were involved in PK2 potentiation of α,β-meATP-induced mechanical allodynia and α,β-meATP-activated currents, since the potentiation were blocked by PK2 receptor antagonist PKRA and selective PKC inhibitor GF 109203X. These results suggested that PK2 facilitated mechanical allodynia induced by α,β-meATP through a mechanism involved in sensitization of cutaneous P2X receptors expressed by nociceptive nerve endings.

Ren C ，Qiu CY ，Gan X ，Liu TT ，Qu ZW ，Rao Z ，Hu WP ... -  《-》

Endothelin-1 enhances acid-sensing ion channel currents in rat primary sensory neurons.

Wu L ，Liu TT ，Jin Y ，Wei S ，Qiu CY ，Hu WP ... -  《-》

Mechanical allodynia caused by intraplantar injection of P2X receptor agonist in rats: involvement of heteromeric P2X2/3 receptor signaling in capsaicin-insensitive primary afferent neurons.

Tsuda M ，Koizumi S ，Kita A ，Shigemoto Y ，Ueno S ，Inoue K ... -  《-》