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Cells
* Department of Physiology, Ca2+-dependent exocytotic pathways in
mouse pancreatic Third Department of Internal Medicine, Faculty of Medicine, University of Tokyo, Bunkyo-ku,
Tokyo 113, Japan
cells were investigated using both
capacitance measurement and amperometric detection
of vesicular contents. Serotonin was preloaded into large dense-core vesicles for the amperometry. Exocytosis was induced by rapid elevation of cytosolic Ca2+
concentrations using caged-Ca2+ compounds. Capacitance measurement revealed two major components of
exocytosis, and only the slow component was accompanied by amperometric events reflecting quantal serotonin secretion. Moreover, the fast and slow exocytoses
induced the two forms of endocytosis that were reported to follow the exocytoses of small-clear and large
dense-core vesicles, respectively. Interestingly, we recorded two types of responses of quantal events: in the
type-1 response, most quantal events occurred with a
delay of 0.2 s and were rapidly exhausted with a time
constant of 1.7 s, while, in the type-2 response, quantal
events occurred with a delay of 2.5 s and were sustained. This suggests the existence of two pathways or
modes of the exocytosis involving large dense-core vesicles. Thus, we have revealed three exocytotic pathways
with divergent fusion kinetics in cells, which provide a
new basis for the understanding of the physiology and
pathology of cells.
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