Spatial attenuation of fluorescein in cytoplasm and free solution. (a) xz section as shown through fluorescein in solution (100 µM), fluorescein conjugated at a latex sphere (10-µm-diam), and the latex sphere in the fluorescein solution. (b) Fluorescein-loaded HECV cell, (c) fluorescein-loaded PC3 cell, (d) GFP-expressing dictyostelium, and (e) fluorescein-loaded human neutrophil shown as phase-contrast image, xy and xz confocal planes. An enlarged version of the xz section of a polarized human neutrophil along the line marked is shown in e′. (f) A similar xz section is shown though two other neutrophils which have not yet “flattened out“ showing the clear attenuation of fluorescence toward the top of the cells. (g) The intensity profile of the free fluorescein and latex-attached fluorescein together with data from the cells shown, using the colored symbols indicated on the images. Bar: (a) 10 µm; (b–e) 25 µm