Contribution of TRPV1-TRPA1 interaction to the single channel properties of the TRPA1 channel

Several lines of evidence suggest that TRPA1 and TRPV1 mutually control the transduction of inflammation-induced noxious stimuli in sensory neurons. It was recently shown that certain TRPA1 properties are modulated by TRPV1. However, direct interaction between TRPA1 and TRPV1 as well as regulation of TRPA1 intrinsic characteristics by the TRPV1 channel have not been examined. To address these questions, we have studied a complex formation between TRPA1 and TRPV1 and characterized the influence of TRPV1 on single channel TRPA1-mediated currents. Co-immunoprecipitation analysis revealed direct interactions between TRPA1 and TRPV1 in an expression system as well as in sensory neurons. Data generated with total internal reflection fluorescence-based fluorescence resonance energy transfer indicate that a TRPA1-TRPV1 complex can be formed on the plasma membrane. The fluorescence resonance energy transfer interaction between TRPA1 and TRPV1 channels is as effective as for TRPV1 or TRPA1 homomers. Single channel analysis in a heterologous expression system and in sensory neurons of wild type and TRPV1 knockout mice demonstrated that co-expression of TRPV1 with TRPA1 results in outward rectification of single channel mustard oil (I_MO) current-voltage relationships (I-V) and substantial modulation of the open probability at negative holding potentials. TRPV1 also does not influence the characteristics of single channel I_MO in Ca ²⁺-free extracellular solution. However, association of TRPA1 with TRPV1 was not affected in Ca²⁺-free media. To assess a role of intracellular Ca²⁺ in TRPV1-dependent modulation of TRPA1 modulation, the TRPA1-mediated single channel WIN55,212-2-gated current (I_WIN) was recorded in inside-out configuration. Our data indicate that single channel properties of TRPA1 are regulated by TRPV1 independently of intracellular Ca²⁺. In summary, our results support the hypothesis that TRPV1 and TRPA1 form a complex and that TRPV1 influences intrinsic characteristics of the TRPA1 channel.