1. ^*Department of Anatomy and Cell Biology, University of Oulu, Oulu, Finland
2. ^†Department of Dermatology, University of Oulu, Oulu, Finland
3. ^‡Department of Surgery, University of Oulu, Oulu, Finland
4. ^§Department of Medical Biochemistry, University of Turku, Turku, Finland
5. ^¶Department of Dermatology, University Hospital of Tampere, Tampere, Finland

Correspondence: Dr Seija-Liisa Karvonen, Department of Dermatology, University Hospital of Oulu, FIN-90220 Oulu, Finland. Email:seija-liisa.karvonen@oulu.fi

²These individuals equally contributed to this study

¹A preliminary report of these results has been presented by the first author at the 29th annual meeting of ESDR in Montpellier in the session ''Epidermal Cell Biology and Differentiation''.

Received 13 October 1999; Revised 7 January 2000; Accepted 11 January 2000.

Abstract

Intracellular calcium plays an important part in the regulation of proliferation and differentiation of keratinocytes. Detached from their in vivo environment, cultured psoriatic keratinocytes were investigated by monitoring free intracellular calcium concentration, which was measured using fura-2/AM as a calcium-sensitive probe. The mean increase in intracellular calcium of psoriatic keratinocytes was significantly reduced compared with control keratinocytes when intracellular calcium stores were mobilized from endoplasmic reticulum with thapsigargin. This finding suggests defective capacitative calcium influx of psoriatic cells. Intracellular calcium stores were similar in psoriatic and control keratinocytes, when extracellular calcium was chelated with ethyleneglycol-bis(-aminoethyl ether)-N,N,N',N',-tetraacetic acid and intracellular calcium was depleted with thapsigargin. Mechanical wounding of keratinocyte monolayer resulted in a significantly reduced rise in intracellular calcium of psoriatic cells in low (<0.1mM) and high (1.8mM) extracellular calcium suggesting defective intercellular coupling of psoriatic keratinocytes. Blocking of gap-junctions with heptanol in wounded keratinocytes did not affect the intracellular calcium response in psoriatic keratinocytes in contrast to healthy keratinocytes. Adding adenosine triphosphate to culture medium resulted in a more pronounced intracellular calcium increase than thapsigargin in psoriatic keratinocytes, suggesting that inositol triphosphate-mediated, P₂-purinergic signaling was enhanced in these cells. Moreover, psoriatic keratinocytes maintained their defective responses up to at least fifth passage suggesting that psoriatic keratinocytes have an inborn error in calcium metabolism, rather than a localized defect in response to altered extracellular calcium gradient observed in vivo.