Figure 3. Excess retrieval and compensatory retrieval: two types of endocytosis that can occur in an individual bovine adrenal chromaffin cell.

Plot of cell capacitance throughout a 25 min recording period. Stimulation protocols are indicated with symbols; above is the total Ca²⁺ entry (Q_Ca) for each protocol. The cell was stimulated with 3 single long duration depolarizations (320, 320 and 640 ms), and each evoked large C_m jumps that were followed by decreases in capacitance. Endocytosis, after the first two long depolarizations, rapidly undershot the pre-stimulus C_m level by >100 fF (Excess retrieval); the third long depolarization evoked exocytosis followed by compensatory retrieval back to the pre-stimulus level. Individual capacitance traces (duration ∼20 s) were aligned manually in Microcal Origin (see Methods); calibration pulses have been eliminated for clarity. (Cell L070908.)