Effect of clustering on the variation of cargo distribution within individual CCPs. (A) BTfnR-expressing cells were incubated in the presence of AF568- or AF647-labeled A1 (top panels) or A4 (bottom panels). Merged images show the extent of colocalization of the differentially labeled SA ligands. (B) Representative scatter plots of the intensities in fluorescent puncta containing both A1s (top) or both A4s (bottom) from a single cell. The spread of the intensities is larger for A4 than for A1, as indicated by the square of the correlation coefficient. (C) Simulation of intensity scatter plot assuming a uniform distribution of cargo capacity and a binomial distribution of colors. (D) Theoretical estimate of maximum cargo capacity based on correlation coefficients.