Figure 4.

Pharmacological treatment alters vesicular quantal size from both intact cells and individual vesicles isolated from cells. (A) Typical peak characteristics representing pharmacological manipulation of vesicular quantal size from both stimulated exocytosis at single PC12 cells and isolated vesicles. Data were collected from matched cell preparations. Cells were incubated with either 100 nM reserpine (a potent VMAT inhibitor) or 100 μM L-DOPA (a precursor in dopamine synthesis) for 90 min prior to stimulated exocytosis investigations and vesicle isolation. (B) Representative normalized frequency histograms describing the distributions of vesicular catecholamine amounts quantified from reserpine-treated (red), untreated (blue), and L-DOPA-treated (black) intact cells that underwent stimulated exocytosis. (C) Representative normalized frequency histograms of vesicular catecholamine amounts quantified from isolated vesicles from reserpine-treated (red), untreated (blue), and L-DOPA-treated (black) matched cell populations in panel B. Data plotted as cubed root amounts. Bin size = 0.2 zmol^1/3. Fits were obtained from a Gaussian distribution of the data. (D) Cumulative analysis for the average number of molecules of catecholamine quantified per vesicle from stimulated exocytosis of intact cells (striped) versus individual isolated vesicles (white) under pharmacological manipulation. The number of events measured for stimulated exocytosis at single cells was 312, 946, and 1376 for reserpine-treated, untreated, and L-DOPA-treated cells, respectively. The number of events measured for the electrochemical cytometry of vesicles was 13 363, 29 643, and 22 270 for reserpine-treated, untreated, and L-DOPA-treated cells, respectively. Error in panel D is SEM.