Mechanisms that play a role in the maintenance of the calcium gradient in the epidermis

Background/purpose: Calcium regulates the proliferation and differentiation of keratinocytes and plays a role in restoration of the epidermal barrier function. The factors that maintain the calcium gradient in vivo are still unknown. A numerical model may give more insight into transport processes that maintain the epidermal calcium gradient. Methods: In this study, transport of free calcium in the epidermis is described with diffusion, convection and electrophoresis. Binding and release of calcium results in equilibrium between free and bound calcium. The physiological epidermal calcium gradient as well as the calcium concentration in a damaged epidermis are modeled. Results: The typical shape of the calcium gradient in the epidermis, as found in experimental studies, was maintained when separate formulations were used for free and bound calcium. Application of damage results in a decrease of the calcium concentration, especially in the upper living epidermis. Using this model, an estimate could be made about the fraction bound calcium in the epidermis. Conclusion: The typical shape of the gradient is predominantly determined by the bound calcium concentration. For both a normal and a damaged epidermis, the concentration of free calcium is mainly determined by electrophoresis in the living epidermis, whereas in the largest part of the stratum corneum diffusion is the most important factor. The convection that was determined by the transepidermal water loss did not have an effect on the calcium concentration.