Evidence for the involvement of peripheral cold-sensitive TRPM8 channels in human cutaneous hygrosensation

In contrast with other species, humans are believed to lack hygroreceptors for sensing skin wetness. Yet, the molecular basis of human hygrosensation are currently unknown and it remains unclear whether we possess a receptor-mediated sensing mechanism for skin wetness. The aim of this study was to assess the role of the cutaneous cold-sensitive Transient Receptor Potential Melatstatin-8 (TRPM8) channel as a molecular mediator of human hygrosensation. To this end, we exploited both the thermal and chemical activation of TRPM8-expressing cutaneous Aδ cold thermoreceptors and we assessed wetness sensing in healthy young males in response to 1) dry skin cooling in the TRPM8-range of thermosensitivity; 2) application of TRPM8-agonist menthol. Our results indicated that: 1) independently of contact with moisture, a cold-dry stimulus in the TRPM8-range of activation induced wetness perceptions across 12 different body regions, and those wetness perceptions varied across the body following regional differences in cold sensitivity; 2) independently of skin cooling, menthol-induced stimulation of TRPM8 triggered wetness perceptions that were greater than those induced by physical dry cooling and by contact with an aqueous cream containing actual moisture. For the first time, we show that the cutaneous cold-sensing TRPM8 channel plays the dual role of cold and wetness sensor in human skin and that this ion channel is a peripheral mediator of human skin wetness perception.