Discussion
Collectively, our findings suggest that proexcitatory mutations of TRPM8, in the context of axonal injury within the cornea, can produce trigeminal ganglion neuron hyperexcitability that contributes to persistent postoperative ocular pain. In addition to providing additional evidence for a role of TRPM8 in human pain, our results suggest that inhibitors of this channel merit future study.
Methods
We conducted a profiling of 2 TRPM8 mutant variants, D665N and V915M, which were identified in patients suffering from persistent pain after LASIK surgery. We used patch-clamp and multielectrode array (MEA) recordings to investigate the biophysical and pharmacologic properties of mutant vs wild-type (WT) channels.
Results
Patch-clamp analysis shows that these mutations shift the activation curves of TRPM8 in a hyperpolarized direction, with this effect being significantly different between WT and D665N channels. In addition, both mutations significantly increase channel sensitivity to the canonical ligand, menthol. MEA recordings from transfected rat trigeminal ganglion neurons indicate that expression of D665N and V915M mutant channels increases spontaneous activity compared with WT channels. Consistent with patch-clamp results, neuronal activity in MEA recordings was increased on exposure to menthol.