Cross-inhibition between native and recombinant TRPV1 and P2X(3) receptors.

Small- to medium-sized neurons in the dorsal root ganglion (DRG) convey nociceptive information to the spinal cord. The co-expression of TRPV1 receptors (sensitive to vanilloids, heat and acidic pH) with P2X(3) receptors (sensitive to extracellular ATP) has been found in many DRG neurons. We investigated whether the co-activation of these two receptor classes in small-diameter cells leads to a modulation of the resulting current responses shaping the intensity of pain sensation. The whole-cell patch clamp method was used to record agonist-induced currents in cultured rat DRG neurons and in HEK293 cells transfected with the respective wild-type recombinant receptors or their mutants. Co-immunoprecipitation studies were used to demonstrate the physical association of TRPV1 and P2X(3) receptors. At a negative holding potential, the P2X(3) receptor agonist alpha,beta-meATP induced less current in the presence of the TRPV1 agonist capsaicin than that in its absence. This inhibitory interaction was not changed at a positive holding potential, in a Ba(2+)-containing superfusion medium, or when the buffering of intrapipette Ca(2+) was altered. The C-terminal truncation at Glu362 of P2X(3) receptors abolished the TRPV1/P2X(3) cross-talk in the HEK293 expression system. Co-immunoprecipitation studies with polyclonal antibodies generated against TRPV1 and P2X(3) showed a visible signal in HEK293 cells transfected with both receptors. It is concluded that the two pain-relevant receptors TRPV1 and P2X(3) interact with each other in an inhibitory manner probably by a physical association established by a motif located at the C-terminal end of the P2X(3) receptor distal to Glu362.