Fig. 9. Receptor de-sensitization is not responsible for the shift in ECAR-Max as cells release more ligand. Cells releasing ligand at 1300 () and 830 () moleculesxcell^-1xminute^-1 as controlled by tetracycline concentration and a ligand-release inhibitor were placed on the cytosensor with () or without () 0.1 µg/ml 225 mAb in the medium. This resulted in both cells with essentially the same number of surface accessible receptors (7500 per cell). The cells were challenged with 40, 20, 5, 2.5, 1.2, 0.6, 0.3, 0.15 ng/ml EGF and the ECAR-Max was determined as described in Fig. 5. The error bars represent the s.e.m. of three experiments in duplicate.