Repair of PM wounds induces CTB endocytosis into uncoated tubular membrane structures. B cells were incubated with gold anti–mouse IgM (18 nm, 10 µg/ml, black arrowheads), biotin-CTB (2 µg/ml) plus gold-streptavidin (10 nm, 2 µg/ml; white arrowheads) at 4°C and then with or without SLO at 37°C for 5 min. (A) Representative TEM images of the tubular invaginations (a–d) and small (e–h) and large vesicles (i–l). Bar, 100 nm. (B) The mean number of tubular membrane structures per cell was counted by visual inspection. (C) The mean percentages per cell of individual types of CTB-containing membrane structures among all CTB-positive vesicles. (D) The mean percentages of individual types of BCR-containing membrane structures among all BCR-positive vesicles per cell. The data were generated from ≥18 randomly selected cell profiles from two individual experiments for each condition. *, P < 0.05; **, P < 0.01; ***, P < 0.001.