Detecting mechanical stimuli is vital to determining our responses to environmental challenges. The speed required for this process suggests ion channels are opened in response to mechanical forces. A specialised membrane protein called the TRPA1 ion channel mediates chemical based pain; however its role in mechanical pain remains unresolved. Here we show that TRPA1 contributes to the detection of mechanical stimuli in a select set of pain sensing neurons. Furthermore, we also show that acute activation of this channel enhances the mechanical responsiveness of these neurons. Finally, we also show that increasing the expression of TRPA1 causes a further enhancement in the mechanical response. These findings suggest that a drug designed to block TRPA1 would be beneficial for the treatment of numerous pathological conditions associated with mechanical pain. Abstract The mechanosensory role of TRPA1 and its contribution to mechanical hypersensitivity in sensory neurons remains enigmatic. We elucidated this role by recording mechanically activated currents in conjunction with TRPA1 over- and under-expression and selective pharmacology. First, we established that TRPA1 transcript, protein and functional expression are more abundant in smaller-diameter neurons than larger-diameter neurons, allowing comparison of two different neuronal populations. Utilising whole cell patch clamping, we applied calibrated displacements to neurites of dorsal root ganglion (DRG) neurons in short-term culture and recorded mechanically activated currents termed intermediately (IAMCs), rapidly (RAMCs) or slowly adapting (SAMCs). Trpa1 deletion (-/-) significantly reduced maximum IAMC amplitude by 43% in small-diameter neurons compared with wild-type (+/+) neurons. All other mechanically activated currents in small- and large-diameter Trpa1 -/- neurons were unaltered. Seventy-three per cent of Trpa1 +/+ small-diameter neurons responding to the TRPA1 agonist allyl-isothiocyanate (AITC) displayed IAMCs to neurite displacement, which were significantly enhanced after AITC addition. The TRPA1 antagonist HC-030031 significantly decreased Trpa1 +/+ IAMC amplitudes, but only in AITC responsive neurons. Using a transfection system we also showed TRPA1 over-expression in Trpa1 +/+ small-diameter neurons increases IAMC amplitude, an effect reversed by HC-030031. Furthermore, TRPA1 introduction into Trpa1 -/- small-diameter neurons restored IAMC amplitudes to Trpa1 +/+ levels, which was subsequently reversed by HC-030031. In summary our data demonstrate TRPA1 makes a contribution to normal mechanosensation in a specific subset of DRG neurons. Furthermore, they also provide new evidence illustrating mechanisms by which sensitisation or over-expression of TRPA1 enhances nociceptor mechanosensitivity. Overall, these findings suggest TRPA1 has the capacity to tune neuronal mechanosensitivity depending on its degree of activation or expression.
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