Recent studies have shown that the behavior of calcium in the epidermis is closely related to the conditions of the skin, especially the differentiation of the epidermal keratinocytes and the permeability barrier function, and therefore a correct understanding of the calcium dynamics is important in explaining epidermal homeostasis. Here we report on experimental observations of in vitro calcium waves in keratinocytes induced by mechanical stimulation, and present a mathematical model that can describe the experimentally observed wave behavior that includes finite-range wave propagation and a ring-shaped pattern. A mechanism of the ring formation hypothesized by our model may be related to similar calcium propagation patterns observed during the wound healing process in the epidermis. We discuss a possible extension of our model that may serve as a tool for investigating the mechanisms of various skin diseases.

Oxytocin is a neuropeptide produced primarily in the hypothalamus and is best known for its roles in parturition and lactation. It also influences behaviour, memory and mental state. Recent studies have suggested a variety of roles for oxytocin in peripheral tissues, including skin. Here we show that oxytocin is expressed in human skin. Immunohistochemical studies showed that oxytocin and its carrier protein, neurophysin I, are predominantly localized in epidermis. RT-PCR confirmed the expression of oxytocin in both skin and cultured epidermal keratinocytes. We also show that oxytocin is released from keratinocytes after application of adenosine 5′-[c-thio]triphosphate (ATPcS, a stable analogue of ATP) in a dose-dependent manner. The ATPcS-induced oxytocin release was inhibited by removal of extracellular calcium, or by the P2X receptor antagonist 2′,3′-O-(2,4,6-trinitrophenyl)adenosine 5′-triphosphate (TNP-ATP). These results suggest that oxytocin is produced in human epidermal keratinocytes and is released in response to calcium influx via P2X receptors.Abbreviations: ATPcS, adenosine 5′-[c-thio]triphosphate; OT, oxytocin; RT, reverse transcription; TNP-ATP, 2′,3′-O-(2,4,6-trinitrophenyl) adenosine 5′-triphosphate.

Ryanodine receptors (RyRs) have an important role as calcium channels in the regulation of intracellular calcium levels in the nervous system and muscle. In the present study, we investigated the expression of RyR in human epidermis. Immunohistochemical studies and reverse transcription-PCR indicated the expression of RyR type 1, 2, and 3 proteins in epidermal keratinocytes. The expression level of each RyR subtype was higher in differentiating keratinocytes than in proliferative cells. We also demonstrated the functional expression of RyR by calcium imaging. In cultured human keratinocytes, application of the RyR agonist 4-chloro-m-cresol (CMC) induced elevation of the intracellular calcium concentration, and co-application of the RyR antagonist 1,1'-diheptyl-4,4'-bipyridinium dibromide (DHBP) blocked the elevation. Application of CMC accelerated keratinocyte differentiation in vitro. On the other hand, topical application of CMC after tape-stripping of hairless mouse skin delayed barrier recovery, whereas application of an RyR antagonist, dantrolene or DHBP, accelerated the barrier recovery. These results suggest that RyR expressed in epidermal keratinocytes is associated with both differentiation of keratinocytes and epidermal barrier homeostasis.

Dry environmental conditions induce a variety of skin pathologies and a recent report indicating that cortisol synthesis in epidermis was increased during wound healing led us to hypothesize that environmental dryness might induce increased cortisol secretion in epidermis. Therefore, we incubated a skin equivalent model under dry (relative humidity: less than 10%) and humid (relative humidity: approximately 100%) conditions for 48 hours and evaluated cortisol secretion and mRNA levels of cortisol-synthesizing enzyme (steroid 11b-hydroxylase, CYP11B1) and IL-1b. Cortisol secretion was increased threefold, and CYP11B1 and IL-1b mRNAs were increased 38-fold and sixfold, respectively, in the dry condition versus the humid condition.Occlusion with a water-impermeable plastic membrane partially blocked the increases in cortisol secretion and CYP11B1 and IL-1b mRNA expression in the dry condition. Thus, environmental dryness might induce increased cortisol secretion in epidermis of diseased skin characterized by epidermal barrier dysfunction, potentially influencing mental state and systemic physiology.Abbreviations: CYP, cytochrome P450; CYP11B1, steroid 11b-hydroxylase (cortisol-synthesizing enzyme); IL-1b, interleukin 1 beta.