Anion requirement and effect of anion transport inhibitors on the response of vero cells to diphtheria toxin and modeccin

The anion requirement for toxic action of diphtheria toxin and modeccin was studied. In Cl − ‐free Hepes buffer made isotonic with mannitol, cells were insensitive to diphtheria toxin and modeccin. Just 2 mM NaCl was sufficient to obtain full toxic activity of modeccin, whereas 140 mM NaCl was required for maximal intoxication with diphtheria toxin. Br − could substitute for Cl − . NO 3 − , I − and ClO 3 − were less efficient than Cl − , whereas SO 4 2− and SCN − were unable to replace Cl − . Cl − deprivation both reduced the ability of cells to bind diphtheria toxin and prevented bound toxin from intoxicating the cells. The binding of modeccin was not reduced. SITS (4‐acetamide‐4′‐isothio‐cyano‐stilbene‐2,2′‐disulfonic acid), an inhibitor of Cl − entry, protected against diphtheria toxin and modeccin, indicating that Cl − transport is required for intoxication.