Figure 5.

Histones, but not Stx, contribute to increased endothelial cell permeability and block APC rescue. Permeability of human aortic endothelial cells was determined by monitoring changes in electrical resistance across a monolayer as described in Section “Materials and Methods.” (A) Steady state resistance observed with media (○) decreases after addition of 1 U/mL (16.85 nM) human thrombin (●), reflecting increased permeability. Challenge with Stx2 (∆) lead to no change in permeability. (B) Increased permeability after thrombin (●) challenge is significantly prolonged if cells are pre-exposed to 50 μg/mL histones (X) for 12 h, but again, Stx2 causes no appreciable change in permeability (∆). (C) Compared to thrombin (2 nM) alone (●), APC pre-exposure (⋆) attenuates thrombin effects on permeability, but cannot rescue permeability of the cells if they have also been exposed to histones (▲). (D) Thrombin increased permeability (●) and APC rescued cells (⋆), but adding 100 ng/mL Stx2 (▼) did not change the protective effect of APC. (E) Permeability data were quantified as area under the curves; mean ± SD of three to four experiments each. Neither Stx1 nor Stx2 alone altered electrical resistance of the monolayers and so Stx2 is shown on graphs as representative of either Shiga toxin. *p < 0.05, ***p < 0.001.