A hyperosmotic stimulus elevates intracellular calcium and inhibits proliferation of a human keratinocyte cell line

Occlusion has previously been used to treat psoriatic plaques and was shown to improve the condition. We investigated the consequences of applying a m echanical stress, in vitro, on the HaCaT keratinocyte cell line. A mechanic al load applied to cells can be mimicked by a hyperosmotic stimulus. Exposu re of HaCaT keratinocytes to different hyperosmotic solutions (final osmola rity in the range 350-600 mOsm, produced by sucrose addition) resulted in a n inhibition of cell proliferation after 96 h of treatment. As keratinocyte maturation is regulated by calcium levels, we measured hyperosmotic-stimul us-induced changes of intracellular calcium ([Ca2+](i)) by single-cell imag e analysis employing FURA-2/AM. The hyperosmotic stimulus produced a rapid transient 2.6-fold elevation of [Ca2+](i) followed by a gradual decay to th e basal level. The transients originated from extracellular as well as from intracellular calcium pools and did not respond to voltage-sensitive calci um channel blockers. The hyperosmotic stimulus was shown to increase the ce llular expression of involucrin, a differentiation marker, following 72 h o f incubation, as measured by flow cytometry. Treatment of cells with the [C a2+](i) chelator BAPTA/AM almost completely blocked the [Ca2+](i) elevation , but did not alter cellular growth or the induction of differentiation obs erved after hyperosmotic stimulus. It is suggested that treatment of kerati nocytes with hyperosmotic stimulus can induce short-time effects (calcium t ransients) as well as long-term cellular maturation.