Fig. 4. The relationship between EGF production, EGFR expression and fraction of EGF captured. (A) Cells were induced to release ligand at the rate of 90 (), 490 (), 780 () and 1700 () moleculesxcell^-1xminute^-1using tetracycline and a ligand-release inhibitor. Fresh medium with 0.0, 0.05, 0.1, 0.5 and 5.0 µg/ml 225 mAb was then added, and the cells were allowed to condition their medium for 8-14 hours. The medium was collected and assayed for EGF by ELISA. Fraction ligand captured was calculated as described in Fig. 2. The concentration of 225 mAb was converted to number of accessible surface receptors as described in Appendix A. The y error bars represent the s.e.m. of a set of data points taken and analyzed in duplicate. The x error bars represent propagated error as described in Materials and Methods. (B) The data presented in Figs 2 () and 4A were used to calculate the effective receptor production rate in moleculesxcell^-1xminute^-1(V_R) at a certain total ligand secretion rate (V_LT) for a given concentration of 225 mAb as outlined in Appendix A. The error bars represent propagated error as described in Materials and Methods. The line through the data is a Gaussian distribution fit by least squares and weighed by the estimated errors.