Sensitization of ASIC3 by proteinase-activated receptor 2 signaling contributes to acidosis-induced nociception

Background: Tissue acidosis and inflammatory mediators play critical roles in pain. Pro-inflammatory agents trypsin and tryptase cleave and activate proteinase-activated receptor 2 (PAR(2)) expressed on sensory nerves, which is involved in peripheral mechanisms of inflammation and pain. Extracellular acidosis activates acid-sensing ion channel 3 (ASIC3) to trigger pain sensation. Here, we show that a functional interaction of PAR(2) and ASIC3 could contribute to acidosis-induced nociception. Methods: Electrophysiological experiments were performed on both rat DRG neurons and Chinese hamster ovary (CHO) cells expressing ASIC3 and PAR(2). Nociceptive behavior was induced by acetic acid in rats. Results: PAR(2)-AP, PAR(2)-activating peptide, concentration-dependently increased the ASIC3 currents in CHO cells transfected with ASIC3 and PAR(2). The proton concentration-response relationship was not changed, but that the maximal response increased 58.7 +/- 3.8% after pretreatment of PAR(2)-AP. PAR(2) mediated the potentiation of ASIC3 currents via an intracellular cascade. PAR(2)-AP potentiation of ASIC3 currents disappeared after inhibition of intracellular G protein, PLC, PKC, or PKA signaling. Moreover, PAR(2) activation increased proton-evoked currents and spikes mediated by ASIC3 in rat dorsal root ganglion neurons. Finally, peripheral administration of PAR(2)-AP dose-dependently exacerbated acidosis-induced nocifensive behaviors in rats. Conclusions: These results indicated that PAR(2) signaling sensitized ASIC3, which may contribute to acidosis-induced nociception. These represent a novel peripheral mechanism underlying PAR(2) involvement in hyperalgesia by sensitizing ASIC3 in primary sensory neurons.