Fig. 7. Fraction of occupied receptors increases as ligand secretion increases. The fraction of occupied receptors was calculated by using the cytosensor data shown in Fig. 6 with the whole cell model outlined in Appendix B and can be calculated based on the total number of occupied receptors () or the number of occupied surface receptors (). The error bars 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. The dashed line (···) represents the data from Fig. 4B.