Expression of the cartilage markers aggrecan and collagen type II and also of IL-1β. Unexposed cultures served as negative controls (control). mRNA was obtained as described in the Materials and methods section. The presence of aggrecan, type II collagen and IL-1β, was detected by RT–PCR. The bar graphs show the integrated optical density of the bands after normalization to β-actin. Values are means and SD. Aggrecan: *p < 0.0002 control versus 'pulsed EMF'; IL-1β: **p < 0.02 control versus 'pulsed EMF'.