Fig. 1.

High density HeLa cells are less sensitive to Shiga toxin but not to diphtheria toxin. Low and high density HeLa cells were treated with tenfold serial dilutions of Shiga toxin (Stx) or diphtheria toxin (DT) for 3 h in leucine-free medium. Cells were then incubated in the presence of [³H]leucine for 20 min, and protein synthesis was measured. IC₅₀ was determined, and the ratio between IC₅₀ of low and high density samples was calculated. One representative experiment is shown for a Stx and b DT. Error bars represent difference between the mean value and two parallels. c The quantification of the ratio between IC₅₀ of high and low density cells + SEM, n = 8 for Stx and n = 4 for DT