Mechanical-stimulation-evoked calcium waves in proliferating and differentiated human keratinocytes

Abstract

Calcium dynamics in the epidermis play a crucial role in barrier homeostasis and keratinocyte differentiation. We have recently suggested that the electro-physiological responses of the keratinocyte represent the frontier of the skin sensory system for environmental stimuli. In the present study, we have evaluated the responses of proliferating and differentiated human keratinocytes to mechanical stress by measuring the intracellular calcium level. Before differentiation, mechanical stress induces a calcium wave over a limited area; this is completely blocked by apyrase, which degrades ATP. In the case of differentiated keratinocytes, the calcium wave propagates over a larger area. Application of apyrase does not completely inhibit this wave. Thus, in differentiated cells, the induction of calcium waves might involve not only ATP, but also another factor. Immunohistochemical studies indicate that connexins 26 and 43, both components of gap junctions, are expressed in the cell membrane of differentiated keratinocytes. Application of octanol or carbenxolone, which block gap junctions, significantly reduces calcium wave propagation in differentiated keratinocytes. Thus, signaling via gap junctions might be involved in the induction of calcium waves in response to mechanical stress at the upper layer of the epidermis.

Mechanosensitive ATP release from hemichannels and Ca2+ influx through TRPC6 accelerate wound closure in keratinocytes

“…It was reported that mechanosensitive ATP release in keratinocytes primarily auto-stimulates P2Y2 receptors and concomitantly triggers Ca 2+ influx through Ca 2+ -permeable channels (Koizumi et al, 2004;Yoshida et al, 2006;Tsutsumi et al, 2009;Boucher et al, 2010;Azorin et al, 2011;Takada et al, 2012;Ho et al, 2013), which then initiates cell migration, the primary process in the wound healing cascade (Dixon et al, 1999;Burrell et al, 2003;Burrell et al, 2005;Braun, et al, 2006;Boucher et al, 2010). We recently suggested that stretch-induced ATP release and a subsequent Ca 2+ increase mediated by P2Y activation (ATP-Ca 2+ signaling) were involved in wound closure in HaCaT keratinocytes (Takada et al, 2012).…”

“…This augmented Ca 2+ increase in differentiated keratinocytes contributes to the continuous renewal of the cornified layer, which is essential for the epidermal barrier function (Tsutsumi et al, 2009). A steep Ca 2+ gradient exists within the normal mammalian epidermis.…”

A flow‐cytometric method for continuous measurement of intracellular Ca2+ concentration

“…These responses have been shown to play a critical role in long established mechanisms such as action potential generation in electrically excitable cells (1,2) and have been implicated in a wide variety of intracellular signaling and regulatory pathways, including initiation of apoptosis (3), alteration of cell surface protein expression (4), and response to mechanical stress on the plasma membrane (5). The vast majority of changes in intracellular calcium is extremely rapid and occurs within a nanosecond timescale.…”

Sustained dynamics of a weakly excitable system with nonlocal interactions

“…(16) and (17). Although it is difficult to obtain analytical expression of a n (ρ) for general ρ, the integration can be performed when ρ < 1/2, which yields…”

“…An example is found in calcium propagation in the epidermis [17], where waves of calcium excitation in epidermal cells have a finite propagation range as opposed to normal excitable waves. Also the wave profile is uniform rather than pulselike, which is different from the cases of propagation failure [18,19].…”