RELEASE OF SECRETORY PRODUCTS DURING TRANSIENT VESICLE FUSION

PATCH-CLAMP experiments have shown that fusion of secretory granules w ith the plasma membrane does not always occur as an all-or-none event, but can develop slowly in a fluctuating manner or can be transient1-5 . These observations suggested that release could be detected during s uch incomplete fusion events. To test this hypothesis we have combined patch-clamp measurements of the activity of single exocytotic fusion pores in beige mouse mast cells with the electrochemical detection of serotonin released during the exocytotic events. We report here that o n fusion pore opening there is a small release of serotonin which is d irectly proportional to the pore conductance. We also show that a sign ificant release occurs during transient fusion events. These results d emonstrate, to our knowledge for the first time, release of a neurotra nsmitter from a secretory vesicle that did not undergo complete fusion .