Nicole Schöbel, Debbie Radtke, Matthias Lübbert, Günter Gisselmann, Ramona Lehmann, Annika Cichy, Benjamin Sven Philip Schreiner, Janine Altmüller, Alan C. Spector, Jennifer Spehr, Hanns Hatt, Christian H.R. Wetzel
- Intracellular \(Cl^{−}\) concentrations \(([Cl^{−}]_{i}\)) of sensory neurons regulate signal transmission and signal amplification. In dorsal root ganglion (DRG) and olfactory sensory neurons (OSNs), \(Cl^{−}\) is accumulated by the \(Na^{+}-K^{+}-2Cl^{−}\) cotransporter 1 (NKCC1), resulting in a \([Cl^{−}]_{i}\) above electrochemical equilibrium and a depolarizing \(Cl^{−}\) efflux upon \(Cl^{−}\) channel opening. Here, we investigate the \([Cl^{−}]_{i}\) and function of \(Cl^{−}\) in primary sensory neurons of trigeminal ganglia (TG) of wild type (WT) and \(NKCC1^{−/−}\) mice using pharmacological and imaging approaches, patch-clamping, as well as behavioral testing. The \([Cl^{−}]_{i}\) of WT TG neurons indicated active NKCC1-dependent \(Cl^{−}\) accumulation. Gamma-aminobutyric acid \((GABA)_{A}\) receptor activation induced a reduction of \([Cl^{−}]_{i}\) as well as \(Ca^{2+}\) transients in a corresponding fraction of TG neurons. \(Ca^{2+}\) transients were sensitive to inhibition of NKCC1 and voltage-gated \(Ca^{2+}\) channels (VGCCs). \(Ca^{2+}\) responses induced by capsaicin, a prototypical stimulus of transient receptor potential vanilloid subfamily member-1 (TRPV1) were diminished in \(NKCC1^{−/−}\) TG neurons, but elevated under conditions of a lowered \([Cl^{−}]_{o}\) suggesting a \(Cl^{−}\)-dependent amplification of capsaicin-induced responses. Using next generation sequencing (NGS), we found expression of different \(Ca^{2+}\)-activated \(Cl^{−}\) channels (CaCCs) in TGs of mice. Pharmacological inhibition of CaCCs reduced the amplitude of capsaicin-induced responses of TG neurons in \(Ca^{2+}\) imaging and electrophysiological recordings. In a behavioral paradigm, \(NKCC1^{−/−}\) mice showed less avoidance of the aversive stimulus capsaicin. In summary, our results strongly argue for a \(Ca^{2+}\)-activated \(Cl^{−}\)-dependent signal amplification mechanism in TG neurons that requires intracellular \(Cl^{−}\) accumulation by NKCC1 and the activation of CaCCs.