Regulated exocytosis of neurotransmitters exhibits
characters of small release quantity (amol) and fast process (ms), which pose high
challenges for its detection. Amperometry at carbon fiber microelectrodes is
perfectly suited to monitor vesicular exocytotic processes at the single cell
level due to its high sensitivity and appropriate temporal resolution. In this
work, the time dependence of catecholamine vesicular exocytosis from PC12 cell under
repeated high potassium stimulations was investigated by amperometry. It was
found that after 20 min of stimulation, a group of small exocytosis spikes
(less than 8 pA) emerges and becomes gradually prominent in the following
responses. These small spikes exhibit significantly faster dynamics than that of
the majority. This fast dynamics can be attributed to swift opening and closing
of the fusion pores. The mechanism underlying this small and fast exocytosis phenomenon
will be discussed.