Exocytosis in colonic goblet cells visualized by video-enhanced light microscopy

In order to develop a method to quantify the mucus secretion, we observed the mucus epithelium of the rabbit colon under a video-enhanced differential interference contrast microscope. Upon stimulation with muscarinic agonists, secretory granules in individual goblet cells were found to undergo a rapid light intensity change. Simultaneously, the lumen was widened and filled with a cloudy material. In each cell, many of such responses were followed by formation of a large cavity which could be recovered after removal of the stimulant. We infer that the light intensity change of a granule arises from exocytosis. Direct counting of the frequency of these quantal responses would be very useful to monitor the secretory activity of single cell in real time at a high sensitivity.