Transient receptor potential A1 mediates an osmotically activated ion channel.

Transient receptor potential (TRP)A1 channel has been implicated in various physiological processes, including thermosensation and pain. A recent study of TRPA1 knockout mice demonstrated deficits in sensing mechanical stimuli, suggesting a role for TRPA1 also in somatic mechanosensation. However, direct evidence of TRPA1 activation by mechanical forces has thus far been lacking. Here we show, using an intracellular calcium assay, that hypertonic solution (HTS) activates TRPA1 channels in human embryonic kidney 293 cells transiently expressing rat TRPA1. In contrast, hypotonic solution has no effect. Single-channel recordings reveal that HTS opens an ion channel that displays similar single-channel conductance to that evoked by the TRPA1 agonist allyl isothiocyanate (AITC) in both recombinant rat TRPA1 cell lines and rat dorsal root ganglia neurons. Ruthenium red reduces the open probability of the single-channel currents and blocks the whole-cell currents evoked by HTS. Camphor also blocks the whole-cell currents evoked by HTS. HTS-activated channel openings are only observed in patches that are also sensitive to AITC. Finally, like AITC, HTS depolarizes the membrane potential of dorsal root ganglia neurons leading to the generation of action potentials. Taken together, these findings indicate that TRPA1 mediates an osmotically-activated ion channel and support a role for TRPA1 in mechanosensation.