Escherichia coli. The reduced form of CTA1 is initially absent in this recombinant toxin, so it was possible to clearly detect the reduction of the CTA1/CTA2 disulfide bond which occurs in the ER. Translocation assays For the translocation assay with exogenously applied CT, HeLa cells were seeded to 6-well plates in complete DMEM medium to achieve an 80% confluent monolayer after an overnight incubation at 37uC. Triplicate wells were required for each condition. To begin the experiment, cells were incubated with DMEM containing 100 ng/ml of GM1 for 1 h at 37uC. After washing, the cells were subsequently incubated 
for 30 min at 4uC with DMEM containing 1 mg/ml of CT. After further washing, the cells were returned to 37uC for 2 h in DMEM containing no additions, 100 mM PBA, or 5 mg/ml of BfA. The cells were then lifted from the 6-well plate using 750 ml of 0.5 mM ethylenediaminetetraacetic acid in phosphate buffered saline. All cells for each condition were collected in a single microcentrifuge tube and spun at 5,0006 g for 5 min. The supernatant was discarded and the pellet was resuspended in 1 ml or 0.1 ml HCN buffer containing 0.04% digitonin. After 10 min on ice, the samples were spun at 16,0006 g for 10 min. Both supernatant and pellet fractions were collected and placed in fresh microcentrifuge tubes. For SPR analysis, supernatant samples were brought to a final volume of 1 ml in HCN buffer and perfused over a sensor slide coated with an Toxicity assays HeLa cells were seeded to 24 well plates and grown overnight to 80% confluency. After a 1 h 37uC incubation with DMEM containing 100 ng/ml of GM1, the cells were challenged with various concentrations of CT in the absence or presence of PBA for 2 h at 37uC. The cells were then washed and exposed to 0.25 ml of ice-cold HCl:EtOH for 15 min on ice. Cell extracts were placed in microcentrifuge tubes and allowed to air dry overnight. cAMP levels were then determined using an ELISA cAMP competition assay kit as per manufacturer instructions. Background cAMP values obtained from unintoxicated cells were subtracted from all experimental values. The maximum cAMP response for the experiment was set to 100%, and all other values were expressed as a ratio of that value. April 2011 | Volume 6 | Issue 4 | e18825 Use of PBA as a Toxin Inhibitor Ileal loop experiments were performed as previously described after approval from the CINVESTAV-IPN Animal Ethical Committee. For studies involving peritoneal injection of PBA, the rats were injected 40 minutes before laparatomy with 100 ml of PBS or 100 ml of 0.18 M PBA. Injected rats were anesthetized with Xylacin and Ketamin to perform laparotomy and expose the small intestines. Four ileal loops of 3 cm with intervening gaps of 2 cm between them were then ligated 20 cm upstream of the ileocecal valve. The loops were injected with 200 ml of CT. Control loops from rats intraperitoneally inoculated with PBS were injected with 200 ml of PBS alone. After injection with CT or PBS, the loops were returned to the abdominal cavity and the incision was sutured. The rats were kept alive for 7 h before sacrifice by buy GSK343 cervical dislocation. Ileal loops were photographed and dissected, and the intestinal contents were collected by gentle pressure. The volume of fluid 10716447 in each loop was measured and expressed as a ratio of the amount of fluid per unit length of loop. Thermal unfolding profiles for CTA1168His6 in the absence or presence of 100 mM PBA were derived from the da Escherichia coli. The reduced form of CTA1 is initially absent in this recombinant toxin, so it was possible to clearly detect the reduction of the CTA1/CTA2 disulfide bond which occurs in the ER. Translocation assays For the translocation assay with exogenously applied CT, HeLa cells were seeded to 6-well plates in complete DMEM medium to achieve an 80% confluent monolayer after an overnight incubation at 37uC. Triplicate wells were required for each condition. To begin the experiment, cells were incubated with DMEM containing 100 ng/ml of GM1 for 1 h at 37uC. After washing, the cells were subsequently incubated for 30 min at 4uC with DMEM containing 1 mg/ml of CT. After further washing, the cells were returned to 37uC for 2 h in DMEM containing no additions, 100 mM PBA, or 5 mg/ml of BfA. The cells were then lifted from the 6-well plate using 750 ml of 0.5 mM ethylenediaminetetraacetic acid in phosphate buffered saline. All cells for each condition were collected in a single microcentrifuge tube and spun at 5,0006 g for 5 min. The supernatant was discarded and the pellet was resuspended in 1 ml or 0.1 ml HCN buffer containing 0.04% digitonin. After 10 min on ice, the samples were spun at 16,0006 g for 10 min. Both supernatant and pellet fractions were collected and placed in fresh microcentrifuge tubes. For SPR analysis, supernatant samples were brought to a final volume of 1 ml in HCN buffer and perfused over a sensor slide coated with an Toxicity assays HeLa cells were seeded to 24 well plates and grown overnight to 80% confluency. After a 1 h 37uC incubation with DMEM containing 100 ng/ml of GM1, the cells were challenged with various concentrations of CT in the absence or presence of PBA for 2 h at 37uC. The cells were then washed and exposed to 0.25 ml of ice-cold HCl:EtOH for 15 min on ice. Cell extracts were placed in microcentrifuge tubes and allowed to air dry overnight. cAMP levels were then determined using an ELISA cAMP competition assay kit as per manufacturer instructions. Background cAMP values obtained from unintoxicated cells were subtracted from all experimental values. The maximum cAMP response for the experiment was set to 100%, and all other values were expressed as a ratio of that value. April 2011 | Volume 6 | Issue 4 | e18825 Use of PBA as a Toxin Inhibitor Ileal loop experiments were performed as previously described after approval from the CINVESTAV-IPN Animal Ethical Committee. For studies involving peritoneal injection of PBA, the rats were injected 40 minutes before laparatomy with 100 ml of PBS or 100 ml of 0.18 M PBA. Injected rats were anesthetized with Xylacin and Ketamin to perform laparotomy and expose the small intestines. Four ileal loops of 3 cm with intervening gaps of 2 cm between them were then ligated 20 cm upstream of the ileocecal valve. The loops were injected with 200 ml of CT. Control loops from rats intraperitoneally inoculated with PBS were injected with 200 ml of PBS alone. After injection with CT or PBS, the loops were returned to the abdominal cavity and the incision was sutured. The rats were kept alive for 7 h before sacrifice by cervical dislocation. Ileal loops were photographed and dissected, and the intestinal contents were collected by gentle pressure. The volume of fluid in each loop was measured and expressed as a ratio of the amount of fluid per unit length of loop. Thermal unfolding profiles for CTA1168His6 in the absence or presence of 100 mM PBA were derived from the da