Fig. 4. EGF induces degradation of Cx43. Cell lysates were prepared as indicated and equal amounts of total cell protein were subjected to SDS-PAGE and western blotting with anti-Cx43 antibodies. As gel loading controls, the blots were stripped and reprobed with anti-actin antibodies. (A) IAR20 cells were treated with 10 µg ml^–1 cycloheximide (chx) alone or in combination with 100 ng ml^–1 EGF. (B) The Cx43 band intensities on gels shown in (A) were measured using Scion Image. The Cx43 band intensities were plotted relative to the intensity of Cx43 bands in untreated cells. (C) Cells were treated with 10 µg ml^–1 cycloheximide and increasing concentrations of EGF for 4 hours. (D) Cells were preincubated with increasing concentrations of PD98059 (µm) for 30 minutes before treatment with 10 µg ml^–1 cycloheximide and 100 ng ml^–1 EGF for 4 hours in the sustained presence of PD98059.