Figure 1. Cellular uptake and endo-lysosomal escape of penetratin. Two different cell types were incubated at 37°C in the continuous presence of fluorescently labeled penetratins (5 µM AFDye532-penetratin and 5 µM NF-penetratin). Time-correlated flow cytometric recording of the fluorescence intensity of cells was performed. The average intensity of AFDye532, characterizing total cellular uptake, and the average intensity of NF-penetratin, characteristic of the amount of penetratin present in pH-neutral compartments, were calculated as a function of time after gating out debris and non-viable cells. The ratio of the two fluorescence intensities is plotted in the panel on the right. The continuous lines show the average fluorescence intensity calculated for 20-sec time periods. The symbols with error bars, representing the standard error of the mean calculated from 13-15 samples from five biological replicates, are only shown for every 7^thdata point for clarity.