Endothelin potentiates TRPV1 via ET(A )receptor-mediated activation of protein kinase C

BACKGROUND: Endothelin-1 (ET-1) both stimulates nociceptors and sensitizes them to noxious stimuli, an effect probably mediated by the ET(A )receptor (ET(A)R) expressed in sensory neurons. The cellular mechanisms of this ET-1-mediated effect are only poorly understood. TRPV1, the heat-, pH- and capsaicin-sensitive cation channel already known to be modulated by a number of cellular mediators released in response to noxious stimuli and during inflammation, is a potential target for the action of ET-1. RESULTS: We studied the effects of ET-1 on TRPV1 in sensory neurons from the dorsal root ganglion (DRG) and in HEK293 cells coexpressing TRPV1 and the ET(A)R. Specific (125)I-ET-1 binding sites (817 ± 92 fmol/mg) were detected in membrane preparations of DRG with an ET(A)R/ET(B)R ratio of 60:40. In an immunofluorescence analysis, coexpression of TRPV1 and the ET(A)R was found in a subpopulation of primary sensory neurons. ET-1 strongly potentiated capsaicin-induced TRPV1 currents in some neurons, and in HEK293 cells co-expressing TRPV1 and the ET(A)R. Weaker potentiation was observed in HEK293 cells coexpressing TRPV1 and the ET(B)R. ET(A)R activation also increased responses to low pH and heat. In HEK293 cells, strong potentiation of TRPV1 like that induced by ET-1 via the ET(A)R could be induced by PKC activation, but not with activators of the adenylyl cyclase or the PKA pathway. Furthermore, inhibition of PKC with bisindolylmaleimide X (BIM X) or mutation of the PKC phosphorylation site S800 completely prevented ET(A)R-mediated potentiation. CONCLUSION: We conclude that ET-1 potentiates TRPV1 by a PKC-dependent mechanism and that this could play a major role in the algogenic and hyperalgesic effects of ET-1 described in previous studies.