Fig. 6. The effective autocrine ligand concentration increases as ligand secretion increases. The effective autocrine ligand concentration was calculated by using the cytosensor data shown in Fig. 5B in conjunction with the whole cell model outlined in Appendix B. The error bars represent propagated error propagated 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.