Figure 3.

Amperometric trace for a nano-tip conical carbon fiber microelectrode pushed against a PC12 cell without breaking into the cytoplasm (a) or placed inside a PC12 cell (b); c) amplified amperometric current trace; d) normalized frequency histograms describing the distributions of vesicular catecholamine amount quantified from untreated PC12 cells by intracellular vesicle electrochemical cytometry (red, n=1017 events from 17 cells) and that from K⁺-stimulated exocytosis at the same electrode (black, n=1128 events from 17 cells). Bin size = 2 x 10⁴ molecules. Fits were obtained from a lognormal distribution of the data.