Endothelin-1 Decreases Excitability of the Dorsal Root Ganglion Neurons via ET_B Receptor.

Endothelin-1 (ET-1) has been demonstrated to be a pro-nociceptive as well as an anti-nociceptive agent. However, underlying molecular mechanisms for these pain modulatory actions remain unclear. In the present study, we evaluated the ability of ET-1 to alter the nociceptor excitability using a patch clamp technique in acutely dissociated rat dorsal root ganglion (DRG) neurons. ET-1 produced an increase in threshold current to evoke an action potential (I _threshold) and hyperpolarization of resting membrane potential (RMP) indicating decreased excitability of DRG neurons. I _threshold increased from 0.25 ± 0.08 to 0.33 ± 0.07 nA and hyperpolarized RMP from -57.51 ± 1.70 to -67.41 ± 2.92 mV by ET-1 (100 nM). The hyperpolarizing effect of ET-1 appears to be orchestrated via modulation of membrane conductances, namely voltage-gated sodium current (I _Na) and outward transient potassium current (I _KT). ET-1, 30 and 100 nM, decreased the peak I _Na by 41.3 ± 6.8 and 74 ± 15.2%, respectively. Additionally, ET-1 (100 nM) significantly potentiated the transient component (I _KT) of the potassium currents. ET-1-induced effects were largely attenuated by BQ-788, a selective ET_BR blocker. However, a selective ET_AR blocker BQ-123 did not alter the effects of ET-1. A selective ET_BR agonist, IRL-1620, mimicked the effect of ET-1 on I _Na in a concentration-dependent manner (IC₅₀ 159.5 ± 92.6 μM). In conclusion, our results demonstrate that ET-1 hyperpolarizes nociceptors by blocking I _Na and potentiating I _KT through selective activation of ET_BR, which may represent one of the underlying mechanisms for reported anti-nociceptive effects of ET-1.

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