Fig. 1. SDS-PAGE and immunoblotting of the chondrocyte membrane treated with various concentrations of retinoic acid, and the effect of retinoic acid pretreatment on MTf expression by chondrocyte cultures. (A) Chondrocytes were exposed or not to 10^–6 M retinoic acid 4 days before the end of incubation. The protein in the crude membrane fraction (6 µg) was analysed by SDS-PAGE and stained with silver. (B) Chondrocytes were exposed to retinoic acid at 0 M, 10^–8 M, 10^–7 M and 10^–6 M 4 days before the end of incubation. The protein in the ConA-bound membrane fraction (2 µg) was analysed by SDS-PAGE and stained with silver. (C) Chondrocytes were exposed to retinoic acid at 10^–6 M 0 hours, 24 hours, 48 hours and 72 hours before the end of the incubation. The proteins in the ConA-bound fraction (2 µg) were resolved by SDS-PAGE and stained with silver. (D) Chondrocytes were exposed to retinoic acid at 10^–6 M 0 hours, 24 hours, 48 hours and 72 hours before the end of the incubation. The MTf level in the chondrocyte cultures was analyzed by immunoblotting. (E) Chondrocytes were exposed, or not exposed, to retinoic acid at 10^–6 M for 4 days (left) and then incubated in the absence of retinoic acid for 3 days (right). The MTf level in the chondrocyte cultures was analysed by immunoblotting. (F) Chondrocytes in confluent cultures were incubated with retinoic acid at 10^–6 M for 4 days. The MTf and GAPDH mRNA levels in the chondrocytes were determined by northern blot analysis.

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