FIG. 2.

Acid pulse-induced entry of toxin B. Endosomal acidification was inhibited with either ammonium chloride or bafilomycin A1. Cells were then subjected to a brief acid pulse at pH 4.0 followed by a return to neutral pH. Samples were followed for 8 h, and cytopathic effects (CPE) were determined by visualization. (a) Bafilomycin inhibitor and pH pulse; (b) ammonium chloride inhibitor and pH pulse. Curves: A, toxin B (pH 7.8); B, toxin B (pH 7.8) plus inhibitor plus acid pulse; C, toxin B predialyzed to pH 4.0; D, toxin B (pH 4.0) plus inhibitor plus acid pulse; E, toxin B (pH 7.8) plus inhibitor; F, toxin B (pH 4.0) plus inhibitor.