Cytotoxic effect of GFP-Etx in 1G11 mouse endothelial cells. 1G11 cells were exposed to increasing concentrations of GFP-Etx for 120 min at 37 °C, and the survival percentage was determined by the MTS assay (A). Around 70% of 1G11 dead cells were detected starting at 10 nM of GFP-Etx exposure compared to about 0% of dead cells detected with the non-toxic form of GFP-pEtx. The CT50 value for 1G11 cells was 2.17 nM (95% CI 1.05 to 4.58) and was 0.58 nM for MDCK cells (95% CI 0.48 to 0.69). Treatment with 50 nM of GFP-Etx on 1G11 cells for 240 min (B) revealed a LT50 of 50.84 min (95% CI 31.67 to 78.35) (*P = 0.02, ****P < 0.00001).