Background: We previously showed that application of hydraulic pressure to cultured human keratinocytes induced elevation of intracellular calcium concentration ([Ca2+]i), but the absolute value of the pressure could not be determined. Purpose: To evaluate the effect of the absolute value of pressure on keratinocytes and other skin cells. Methods: In the present work, we examined the effect of changes in absolute pressure level by observing the [Ca2+]i responses of cultured human keratinocytes and other cells cultured at the bottom of a hermetically sealed plastic flask as the air pressure in the flask was increased gradually, held stable, and then decreased abruptly, using the Ca2+-indicator fura-2. Results: We found that the [Ca2+]i of differentiated keratinocytes was changed significantly in each phase, whereas undifferentiated keratinocytes and other cells derived from skin or dorsal root ganglion showed no response. Removal of calcium from the medium blocked the increase in [Ca2+]i in differentiated keratinocytes. The [Ca2+]i responses of individual differentiated keratinocytes in the increasing, stable and decreasing phases of pressure change varied from cell to cell. The threshold of air-pressure increase from the original level for inducing [Ca2+]i response was 5 - 20 hPa. Conclusion: These results suggest that epidermal keratinocytes might contain a sensory system that detects changes of external pressure on the skin.
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