Contribution of transient receptor potential vanilloid subfamily 1 to endothelin-1-induced thermal hyperalgesia

Endothelin-1 (ET-1) plays an important role in peripheral pain processing. However, the mechanisms of the nociceptive action of ET-1 have not been fully elucidated. In this study, we investigated the contribution of transient receptor potential vanilloid subfamily 1 (TRPV1) to ET-1-induced thermal hyperalgesia. Intraplantar ET-1-induced thermal hyperalgesia was examined by assessing the paw withdrawal latency to noxious heat stimuli. In electrophysiological study, whole-cell patch-clamp recordings were performed to investigate the interaction of ET-1 and TRPV1 using human embryonic kidney 293 (HEK293) cells expressing endothelin type A receptor (ETA) and TRPV1. Intraplantar ET-1 (3, 10 and 30 pmol) produced thermal hyperalgesia in a dose-dependent manner. Thermal hyperalgesia was attenuated by the inhibition of ETA and protein kinase C (PKC) but not that of ETB. ET-1-induced thermal hyperalgesia was significantly attenuated in TRPV1-deficient mice compared with that in wild-type mice. In voltage-clamp experiments, 10 nM capsaicin evoked small inward currents in HEK293 cells expressing TRPV1 and ETA. In the presence of ET-1, capsaicin produced much larger current responses (P<0.05). Mutation at PKC-specific TRPV1 phosphorylation sites (S800A/S502A) and PKC inhibitors inhibited the potentiating effect of ET-1. In addition, ET-1 decreased the temperature threshold for TRPV1 activation in a PKC-dependent manner (from 41.0±0.4 °C to 32.6±0.6 °C). In addition, Western blot analysis was also performed to confirm ET-1-induced phosphorylation of TRPV1. Incubation of ET-1 and intraplantar ET-1 evoked phosphorylation of TRPV1 in HEK293 cells expressing TRPV1 and ETA and the skin, respectively. These results suggest that the sensitization of TRPV1 activity through an ETA-PKC pathway contributes to ET-1-induced thermal hyperalgesia.