Fig. 4.

The depolarization-induced increase in intravesicular fluorescence requires a pH gradient. Cells were initially superfused with normal saline containing a pH-collapsing agent [1 μm monensin (A), 1 μm nigericin (B), or 1 μm FCCP (C)] and then with 100 mm K⁺ saline containing the same pH-collapsing agent. Note that fluorescence decrease occurred almost immediately after 100 mmK⁺ application. D, Comparison of delay from the application of 100 mm K⁺to the onset of fluorescence decrease in cells without pretreatment (C) and those pretreated with monensin (M), nigericin (N), or FCCP (F). n = 11, 8, 5, and 5 for control, monensin, nigericin, and FCCP, respectively. *p < 0.01 versus control.