Zusammenfassung
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) ...
Zusammenfassung
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 Ca2+ transients in a corresponding fraction of TG neurons. Ca2+ transients were sensitive to inhibition of NKCC1 and voltage-gated Ca2+ channels (VGCCs). Ca2+ 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 Ca2(+-)activated Cl- channels (CaCCs) in TGs of mice. Pharmacological inhibition of CaCCs reduced the amplitude of capsaicin-induced responses of TG neurons in Ca2+ 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 Ca2+-activated Cl--dependent signal amplification mechanism in TG neurons that requires intracellular Cl- accumulation by NKCC1 and the activation of CaCCs.
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