Closure of the mouth to a fused vesicle was dependent on dialysis time and independent of dynamin activity. (A) Comparison of the change in capacitance (red) and the IRM signal (black) triggered by a depolarization lasting 0.5 s. Simultaneous measurements were made in nine cells, and only synchronous IRM signals were averaged. Both measurements are normalized. In A–D, the dashed line indicates the baseline levels of capacitance and reflected light and error bars indicate SEM. (B) Intracellular dialysis with 480 μM of amphiphysin-SH3 domain blocked endocytosis assayed by capacitance (red; n = 5), but the IRM signal recovered normally (black; n = 7). (C) Intracellular dialysis with 1 mM GTP-γ-S blocked endocytosis assayed by capacitance (red; n = 11). The IRM signal recovered to baseline, although more slowly than controls in A. (D) Simultaneous capacitance and IRM recording in a cell dialyzed for 18 min. The stimulus was a train of 5 × 200-ms depolarizations.