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

<bold>Background: </bold>Tissue acidosis and inflammatory mediators play critical roles in pain. Pro-inflammatory agents trypsin and tryptase cleave and activate proteinase-activated receptor 2 (PAR2) 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 PAR2 and ASIC3 could contribute to acidosis-induced nociception.<bold>Methods: </bold>Electrophysiological experiments were performed on both rat DRG neurons and Chinese hamster ovary (CHO) cells expressing ASIC3 and PAR2. Nociceptive behavior was induced by acetic acid in rats.<bold>Results: </bold>PAR2-AP, PAR2-activating peptide, concentration-dependently increased the ASIC3 currents in CHO cells transfected with ASIC3 and PAR2. The proton concentration-response relationship was not changed, but that the maximal response increased 58.7 ± 3.8% after pretreatment of PAR2-AP. PAR2 mediated the potentiation of ASIC3 currents via an intracellular cascade. PAR2-AP potentiation of ASIC3 currents disappeared after inhibition of intracellular G protein, PLC, PKC, or PKA signaling. Moreover, PAR2 activation increased proton-evoked currents and spikes mediated by ASIC3 in rat dorsal root ganglion neurons. Finally, peripheral administration of PAR2-AP dose-dependently exacerbated acidosis-induced nocifensive behaviors in rats.<bold>Conclusions: </bold>These results indicated that PAR2 signaling sensitized ASIC3, which may contribute to acidosis-induced nociception. These represent a novel peripheral mechanism underlying PAR2 involvement in hyperalgesia by sensitizing ASIC3 in primary sensory neurons. [ABSTRACT FROM AUTHOR]