Fig. 2.

(A) Comparison of the mean fluorescence intensity of EGF-Atto 647N measured in A431 cells after binding to saturating (100 nM) or subsaturating (1 nM) concentrations of EGF-Atto 647N, with or without prebinding of MAb 2E9. Also shown are the results of binding a saturating concentration of EGF after exposure to PMA. Each result was obtained from measurement of >500 cells. Error bars represent the standard errors of the means. (B) Mean fluorescence lifetime of EGF-Atto 488 bound to EGFR in A431 cell membranes after exposure to 0.5 nM, 1 nM, and 100 nM concentrations of EGF-Atto 488 obtained from 20, 27, and 54 cells, respectively. Error bars represent the standard deviations of the mean lifetimes.