Fig. 10. Whole-cell modeling, with endogenous ligand concentration determined from microphysiometer experiments, predicts the occupancy of surface receptors on autocrine cells. Nearly confluent monolayers of autocrine cells secreting different levels of ligand as controlled by tetracycline and a ligand-release inhibitor were incubated with 0.6 µg/ml ¹²⁵I-13A9 mAb, an EGFR non-blocking antibody, for 3 hours at 37°C. ¹²⁵I-13A9 mAb was removed by acid stripping as described in Materials and Methods to determine the number of surface receptors (). Using whole-cell kinetic modeling as described in Appendix B, the predicted total number of surface receptors was determined (). The error bars for the radiolabeling results represent the s.e.m. of two to five experiments in triplicate. The error bars for the modeling results represent propagated error from the s.e.m. of receptor synthesis rate, the s.e.m. of the fraction of ligand degraded, the s.e.m. of the ligand production rate, and the standard error of the estimate associated with the ECAR-Max curve fits.