Temporal and spatial monitoring of exocytosis with native fluorescence imaging microscopy

Exocytosis of rat peritoneal mast cells (RPMCs) was monitored temporally and spatially using native fluorescence imaging microscopy with 305-nm laser excitation. Real time chemical images of the relative amounts of serotonin and protein released from each cell are obtained. Individual cells released different amounts of material and the time delay of the release event after stimulation by polymyxin varied from cell to cell. Release consisted of a main burst of activity followed by slow sustained secretion over many seconds. The images show that different regions of a given cell behave asynchronously in releasing material into the surrounding medium. On rare occasions, highly localized fluorescence bursts can be seen in the vicinity of the cell. Presumably, these are due to delayed release of fluorescent mediators from single granules, following detachment of the latter from the cell. These quantitative fluorescence measurements allow one to follow the time-course of the physiologically important parameter---the amount of material that is secreted into the body fluid on stimulation.