FIGURE 2.

Keratinocytes are postulated touch receptors. (A) Depiction of keratinocytes (brown) and an afferent fiber (purple) in the epidermis. Tactile stimuli impinged on the skin activate the mechanically gated cationic channel Piezo1, leading to release of ATP from these cells and subsequent activation of the purinergic P2X4 receptors in sensory afferents (Coste et al., 2010; Baumbauer et al., 2015; Mikesell et al., 2022). (B) Schematic representation of key results obtained by Moehring et al. (2018) that support a role of purinergic signaling in keratinocytes to afferent communication. Top panel, a 40 nN force applied onto a mouse skin-nerve preparation induces action potentials in a C-fiber. Action potentials are depicted here as vertical purple lines. The action potentials are fewer in a skin-nerve preparation treated with the ATP hydrolyzing enzyme apyrase, and in a skin-nerve preparation from a mouse in which the P2X4 receptor was knocked down in sensory neurons using the cre/lox system and the sensory neuron-Advillin promoter. Bottom panel, same as the top panel but with an αδ fiber [adapted from Moehring et al. (2018)].