Transient receptor potential (TRP) channels are polymodal receptors that are activated by multiple external and endogenous stimuli.
6,7 The TRP superfamily is composed of 28 different genes that are subdivided into seven different subfamilies with variable cation permeability (TRPA, TRPC, TRPM, TRPML, TRPN, TRPP, and TRPV).
8 Among them, TRP vanilloid subtype 1 (TRPV1), the capsaicin receptor, is the prototype of the family members and is a nocioceptor. It elicits responses to a variety of noxious stimuli, including chemical irritants, inflammatory mediators, alterations in pH, moderate heat (≥43°C), and hypertonicity.
9 All these stimuli lead to nocioceptions and can evoke pain or pain-related behavior in animals.
10–13 TRPV1 activation reportedly induces the release of tachykinin neuropeptides (e.g., substance P, neurokinin A, and calcitonin gene–related peptide) from the sensory nerves, inducing neurogenic inflammation.
14,15 Although TRPV1 was originally found as a neuronal component, epidermal keratinocytes or mucosal epithelial cells also express TRPV1 to presumably exert a sensory function or modulation of the inflammatory response to external stimuli.
16,17 By using cell culture experiments, we have shown that the TRPV1 channel is required for cell migration in association with calcium ion influx.
18 We have also demonstrated that TRPV1 is constitutively expressed in human, rabbit, and mouse corneal epithelium in vivo and that TRPV1 activation induces increased the proliferation and migration of SV40-immortalized human corneal epithelial cells through epidermal growth factor receptor transactivation, which leads to global MAPK pathway stimulation.
19,20